Konzepte und Entscheidungshilfen zur Verbesserung der Eutergesundheit in der Trockenstehphase von
Milchkühen in ökologisch wirtschaftenden Milchviehbetrieben
INAUGURAL – DISSERTATION zur Erlangung des Grades eines Doktors
der Veterinärmedizin
- Doctor medicinae veterinariae – (Dr. med. vet.)
vorgelegt von
Klemens Rochus Kiesner Eckernförde
Hannover 2017
Fakultät II, Abteilung für Bioverfahrenstechnik – Mikrobiologie
Hochschule Hannover
1. Gutachter: Prof. Dr. Volker Krömker
2. Gutachter: Prof. Dr. Nicole Kemper
Tag der mündlichen Prüfung: 02.05.2017
Die Versuche dieser Arbeit wurden aus Mitteln des Landes Niedersachsen und des Europäischen Fonds für regionale Entwicklung gefördert.
Kiesner, K., Volling, O., Knorr, N., Krömker, V.
Untersuchungen zum Trockenstellen auf Biobetrieben – Kriterien zur Entscheidungsfindung
Tagung der Arbeitsgruppe Sachverständigenausschuss Subklinische Mastitis der DVG Fachgruppe Milchhygiene
Hannover, 12. und 13.3.2015
Kiesner, K., Knorr, N., Zhang, Y., Volling, O., Krömker, V.
Neuinfektionsrate von bovinen Milchdrüsen nach Applikation eines Bismuthsubnitrat- freien internen Zitzenversieglers (Poster)
Tagung der Arbeitsgruppe Sachverständigenausschuss Subklinische Mastitis der DVG Fachgruppe Milchhygiene
Hannover, 12. und 13.3.2015
Kiesner, K., Knorr, N., Volling, O., Krömker, V.
Selektives Trockenstellen auf Biobetrieben – Entscheidungshilfen Mastitisnachmittag: Forschung für die Praxis
Hannover, 1.4.2016
Klemens R. Kiesner, Nicole Wente, Otto Volling, Volker Krömker Dry cow therapy on organic farms – Selection criteria (Poster) 29th World Buiatrics Congress
Dublin, 3. – 7.7.2016
Meinen Eltern
2. Publikation I: Selection of cows for treatment at dry-off on organic dairy farms 16
2.1 Zusammenfassung ... 17
2.2 Abstract... 18
2.3 Introduction ... 19
2.4 Material and methods ... 20
2.5 Results ... 23
2.6 Discussion ... 32
2.7 Conclusion ... 36
2.8 References ... 37
3. Publikation II: New infection rate of bovine mammary quarters after application of a bismuth subnitrate-free internal teat sealant at dry-off ... 40
3.1 Zusammenfassung ... 41
3.2 Abstract... 42
3.3 Introduction ... 43
3.4 Material and methods ... 44
3.5 Results ... 46
3.6 Discussion ... 47
3.7 Acknowledgments ... 50
3.8 References ... 51
4. Diskussion ... 53
4.1 Euterpathogene auf ökologischen Betrieben ... 53
4.2 Identifikation infizierter Tiere zum Trockenstellen ... 54
4.5 Prototyp des Bismuthsubnitrat-freien internen Zitzenversieglers ... 57
4.6 Entscheidungshilfe ... 58
5. Zusammenfassung ... 62
6. Summary ... 65
7. Literaturverzeichnis ... 67
8. Danksagung ... 75
1. Einleitung
Mastitis bezeichnet eine Entzündung der bovinen Milchdrüse, meist infektiöser Ätiologie. Sie ist der kostenintensivste Krankheitskomplex in der Milchviehhaltung mit ökonomischen Verlusten durch reduzierte Milchleistung, verminderte Milchqualität, Behandlungskosten, nicht verkehrsfähige Milch nach Behandlung (Sperrmilch), zusätzliche Arbeit und vorzeitige Abgänge von Tieren (International Dairy Federation, 2005; Hogeveen et al., 2011). Auch auf ökologischen Betrieben sind Eutergesundheitsstörungen eine maßgebliche Ursache krankheitsbedingter Kosten und weisen die höchste Inzidenz aller klinischen Erkrankungen auf (Volling et al., 2005). Die meisten Anwendungen von Arzneimitteln fallen auf sie zurück (Krömker und Volling, 2007).
Unter subklinischer Mastitis versteht man eine Entzündung ohne äußerlich erkennbare Symptome aber mit erhöhtem somatischem Zellgehalt. Sie ist die häufigste Auftrittsform der Krankheit und verursacht die größten ökonomischen Verluste. Die Milchproduktionsminderung auf Grund erhöhter somatischer Zellzahlen wird aber oft in ihrer Bedeutung unterschätzt (International Dairy Federation, 2005;
Deutsche Veterinärmedizinische Gesellschaft, 2012). Studien haben gezeigt, dass ein geringerer Anteil von Tieren mit somatischen Zellgehalten von über 100.000 Zellen/ml an der Gesamtherde sowohl auf konventionellen als auch auf ökologischen Betrieben zu weniger Verlusten und höheren Gewinnen führt (Jahnke, 2004; Volling et al., 2005).
Die Eutergesundheitssituation in einem Milchviehbetrieb wird durch die Dauer bestehender Infektionen und das Auftreten von Neuinfektionen bestimmt (Dodd, 1981). Maßnahmen zur Verbesserung der Eutergesundheit beinhalten unter anderem die unmittelbare Behandlung klinischer Mastitiden mit Antibiotika, die antibiotische Versorgung zu Beginn der Laktationsruhe, die Merzung chronisch infizierter Tiere, eine verbesserte Melkhygiene, die Zitzendesinfektion nach dem Melken, verbesserte Haltungsbedingungen, sowie die Melkmaschinenkontrolle und –korrektur (Neave et al., 1966; Dodd et al., 1969; Kingwill et al., 1970; Eberhart, 1986; Dingwell et al., 2003;
Mein et al., 2004). Die ersten drei genannten Maßnahmen zielen dabei vor allem auf eine Verkürzung der Infektionsdauer, während die übrigen die Neuinfektionsrate senken sollen.
Je nach Zeitpunkt der Anwendung der Antibiotika unterscheidet man zwischen der Therapie während der Laktation und der einmaligen intramammären Applikation eines Langzeitantibiotikums zu Beginn der Laktationsruhe (Trockenstelltherapie). Die Laktationsruhe, auch Trockenstehphase genannt, erstreckt sich vom letzten Melken der Kuh bis zur Kalbung und dauert durchschnittlich 51 bis 60 Tage (Bachman und Schairer, 2003).
Der effektivste Zeitpunkt zur Behandlung von subklinischen Mastitiden ist zum Trockenstellen (National Mastitis Council, 2006; Landin et al., 2011). Während der Laktation entspricht je nach Erreger die Heilungsrate nach Therapie oft nur der Selbstheilungsrate (Wilson et al., 1999). Die Applikation eines antibiotischen Trockenstellers zu Beginn der Trockenstehphase hingegen führt zu einer signifikant höheren Heilungswahrscheinlichkeit im Vergleich zu unbehandelten Vierteln. Die Heilungsrate liegt dabei im Mittel bei 78 % (Halasa et al., 2009). Im Jahr 2013 wurden 9,2 Millionen antibiotische Trockensteller in Form von Injektoren in Deutschland abgegeben und rund 80 % aller Milchkühe antibiotisch trockengestellt (Wallman, 2014).
Nach den Richtlinien des ökologischen Landbaus ist jedoch die Anwendung von Antibiotika zum Trockenstellen limitiert (Rat der Europäischen Union, 2007;
Europäische Kommission, 2008). Antibiotische Trockensteller sollen nur bei
„Problemtieren mit medizinischer Indikation und Erregernachweis“ eingesetzt werden (Bioland e.V., 2015). Eine Folge dieser Beschränkung ist eine im Vergleich zu konventionellen Betrieben schlechtere Eutergesundheit (Krömker und Volling, 2013).
Aufgrund niedriger Heilungs- und hoher Neuinfektionsraten in der Trockenstehphase ist insbesondere die Mastitisprävalenz zum Kalbezeitpunkt hoch (Krömker et al., 2009). Weiterhin dominieren auf ökologischen Betrieben Infektionen mit kontagiösen Erregern wie Staphylococcus aureus, während auf konventionellen Betrieben durch die beschriebenen Bekämpfungsmaßnahmen eine relative Verschiebung in der Prävalenz von kontagiösen Mastitiserregern zu Umweltkeimen wie Streptococcus uberis und Escherichia (E.) coli stattfindet (Bradley, 2002; Hayton und Bradley, 2004).
Jedoch steht in der konventionellen Milchviehhaltung wie in der Nutztierhaltung insgesamt der Einsatz von Antibiotika durch befürchtete Resistenzbildungen
zunehmend in der Kritik (Oliver et al., 2011). Jeder Einsatz antibakterieller Wirkstoffe in der Veterinär- und in der Humanmedizin fördert die Selektion von Resistenzen (Kaspar et al., 2015).
Mit der Deutschen Antibiotika-Resistenzstrategie (DART) hat die deutsche Bundesregierung im Jahr 2008 ein Konzept vorgelegt und nachfolgend umgesetzt, um die weitere Entwicklung und Ausbreitung von Antibiotika-Resistenzen zu reduzieren.
Im Bereich der Veterinärmedizin zielen die darin beschriebenen Maßnahmen auf eine Reduktion der Häufigkeit von Antibiotikatherapien und der absoluten Menge der bei Tieren eingesetzten Antibiotika. Im Jahr 2014 wurden in der Tiermedizin insgesamt 1238 t und damit im Vergleich zum Vorjahr ungefähr 15 % weniger Antibiotika abgegeben. Das ergab die Auswertung der im Jahr 2014 zum vierten Mal erhobenen Abgabemengendaten für Antibiotika durch das Bundesamt für Verbraucherschutz und Lebensmittelsicherheit (BVL). Die Abgabemenge der für die Therapie beim Menschen besonders bedeutenden Antibiotikaklassen, darunter Cephalosporine der 3. und 4.
Generation, hatte jedoch nicht abgenommen und stagnierte auf dem Niveau des Vorjahres. Wirkstoffe dieser Klasse finden sich auch in antibiotischen Trockenstellpräparaten. So stammten nach absoluten Zahlen des BVL 921.000 Injektoren und damit zehn Prozent der abgegebenen antibiotischen Trockensteller im Jahr 2013 aus der Gruppe der Cephalosporine der 4. Generation (Wallman, 2014).
Laut Beurteilung der Weltgesundheitorganisation (WHO) gehören Cephalosporine der 3. und 4. Generation zu den Wirkstoffen mit höchster Priorität für die Humanmedizin, unter anderem für die Behandlung bei Meningitis und salmonellenbedingten Krankheiten bei Kindern (WHO Advisory Group on Integrated Surveillance of Antimicrobial Resistance, 2011).
Bisher zeigen Bakterienisolate von an Mastitis erkrankten Kühen nach Auswertungen des BVL insgesamt niedrige Resistenzraten. Bei der Spezies E. coli findet sich jedoch ein Anstieg von zwei auf neun Prozent. Noch deutlichere Resistenzbildung von E. coli findet sich in Isolaten von an Enteritis erkrankten Kälbern.
Die Raten Extended-Spectrum-Betalaktamase bildender E. coli beim Kalb liegen bei ungefähr 34 % (Kaspar et al., 2015).
Eine Erklärung für die Unterschiede in der Resistenzentwicklung kann die vor allem im Vergleich zum Intestinaltrakt geringe Anzahl von Bakterien im Euter sein. Daher ist das Risiko von Resistenzentwicklung nach intramammärer Applikation von Antibiotika weniger wahrscheinlich als bei oraler oder parenteraler Verabreichung. Jedoch gibt es durch die Verfütterung von Sperrmilch an Kälber möglicherweise eine Beziehung zwischen intramammärer Anwendung und Resistenzbildung bei intestinalen Bakterien. Milch, die während der Wartezeit anfällt, enthält häufig Spuren von Antibiotika und kann so zu Selektionsdruck auf Bakterien im Intestinaltrakt des Kalbes führen. Ähnliche Prozesse sind für Antibiotika belastetes Kolostrum nach Anwendung antibiotischer Trockensteller vorstellbar (Lam et al., 2014).
Bezogen auf die Gesamtmenge der in der Tiermedizin eingesetzten Antibiotika (Stand 2013) machen die zur intramammären Anwendung abgegebenen Antibiotika (Laktations- und Trockenstelltherapie) nur 0,75 % aus (Wallman, 2014). Gleichzeitig birgt jedoch insbesondere das antibiotische Trockenstellen ein hohes Einsparpotential.
Durch den selektiven Einsatz von antibiotischen Trockenstellern nur bei bestimmten Tieren (selektives Trockenstellen) kann die Menge eingesetzter Antibiotika annähernd um 50 % gesenkt werden (Rindsig et al., 1978; Cameron et al., 2014). Die Heilungsrate liegt dabei zwar unter der vom generellem antibiotischem Trockenstellen, ist aber im Vergleich zu keiner Therapie signifikant höher (Halasa et al., 2009).
Zum Zeitpunkt des Trockenstellens infizierte Tiere sollten auch beim selektiven Trockenstellen antibiotisch versorgt werden, andernfalls kommt es zu ökonomischen Verlusten (Berry et al., 2004). Demzufolge bedarf es geeigneter Methoden zur Identifikation infizierter Tiere (Huxley et al., 2002; Robert et al., 2008). Die sterile Milchprobenentnahme und zytobakteriologische Untersuchung jedes Euterviertels aller Tiere zum Trockenstellen erscheint dabei wenig praktikabel und kostenaufwendig (Eberhart, 1986; Sargeant et al., 2001). Die am häufigsten genutzte Selektionsmethode basiert auf den monatlichen in der Milchleistungsprüfung (MLP) erfassten somatischen Zellzahlen im Einzelgemelk und erzielt je nach gewähltem Grenzwert und Anzahl der einbezogenen Monate unterschiedliche Ergebnisse (Rindsig et al., 1979; Sargeant et al., 2001; Bradley und Green, 2004; Torres et al., 2008; Pantoja et al., 2009; Biggs et al., 2016). Weitere in der Literatur beschriebene
Verfahren gründen auf der Mastitisgeschichte des Einzeltiers in der Laktation (Rindsig et al., 1979; Torres et al., 2008), dem Schalmtest zur indirekten Abschätzung der Zellzahl (Rindsig et al., 1979; Sargeant et al., 2001; Sanford et al., 2006; Bhutto et al., 2012), sowie bakteriologischen Schnelltests wie dem Petrifilm (Cameron et al., 2014).
Auch wenn infizierte Kühe korrekt selektiert wurden, beeinflussen verschiedene Faktoren die Wahrscheinlichkeit der Heilung nach einer Therapie und chronisch infizierte Tiere mit geringer Aussicht auf Heilung sollten eher gemerzt werden (Osterås et al., 1999).
Da auf ökologisch wirtschaftenden Betrieben bei möglichst geringer allopathischer Behandlung die Kühe auch eine lange Nutzungsdauer erreichen sollen und dementsprechend Merzungen nur bedingt vorgenommen werden können, ist insgesamt eine Verbesserung der Eutergesundheit durch eine Verkürzung der Infektionsdauer schwierig zu erreichen. Folglich ist die Optimierung überwiegend durch eine Senkung der Neuinfektionsrate möglich (Krömker und Volling, 2013).
Während der Trockenstehphase besteht ein hohes Risiko für Neuinfektionen (Oliver und Mitchell, 1983). So sind über 98 % der beim Kalben festgestellten Infektionen Neuinfektionen (Bradley et al., 2011). Vor allem zu Beginn der Trockenstehphase, während der aktiven Involution, und zum Ende hin, während der beginnenden Laktogenese/Kolostrogenese, ist die Milchdrüse besonders empfindlich gegenüber neuen Infektionen (Smith et al., 1985; Oliver und Sordillo, 1989; Dingwell et al., 2004).
In der Phase der aktiven Involution steigt das Risiko durch den Wegfall des Melkens, die dadurch fehlende Spülung von Bakterien aus dem Strichkanal und das Aussetzten der Zitzendesinfektion. Weiterhin findet zunächst eine Ansammlung von Sekret in der Milchdrüse statt und der intramämmere Druck und das Risiko von Milchlaufenlassen steigen. Die Phagozytose der angesammelten Milch und degenerierter Epithelzellen führt zudem zu einer Auslastung von Immunzellen (Smith und Todhunter, 1982;
Bradley und Green, 2004). Der Übergang zur Laktogenese stellt ebenfalls eine kritische Phase dar (Oliver und Mitchell, 1983). Mit dem Einsetzen der Kolostrumbildung werden antimikrobielle Substanzen im Euter zunehmend verdünnt, zudem ist die Leukozytenfunktion beeinträchtigt (Smith und Todhunter, 1982; Bradley und Green, 2004).
In der dazwischenliegenden Zeit, wenn die Involution abgeschlossen ist und sich ein Keratinpropf im Zitzenkanal als natürliche Barriere gegen eindringende Bakterien gebildet hat, ist das Drüsengewebe weitestgehend resistent gegenüber Infektionen (Dingwell et al., 2004). Obwohl der zeitnahe Verschluss des Zitzenkanals durch den Keratinpropf ein entscheidender Schutzmechanismus ist, verschließen sich 50 % aller Zitzen nicht innerhalb der ersten Woche und über 20 % bleiben bis zur sechsten Woche offen mit der Folge eines deutlich erhöhten Neuinfektionsrisikos (Williamson et al., 1995; Dingwell et al., 2004). Die Applikation einer beständigen Substanz in Form eines internen Zitzenversieglers bietet ähnlich wie der natürliche Keratinpropf die Möglichkeit das Eindringen von Pathogenen durch den Zitzenkanal zu erschweren (Meaney, 1977; Woolford et al., 1998). In einer Metaanalyse von Rabiee und Lean (2013) mit 12 Studien, konnte die alleinige Anwendung eines internen Zitzenversieglers im Vergleich zu unbehandelten Vierteln die Wahrscheinlichkeit einer Neuinfektion um 73 % senken. Verglichen mit der alleinigen antibiotischen Therapie, die ebenfalls Schutz vor Neuinfektion bietet (Bradley und Green, 2004), reduzierten interne Zitzenversiegler (mit und ohne zusätzlicher antibiotischer Therapie) das Risiko um 25 % (Rabiee und Lean, 2013). Da sie keine Antibiotika enthalten, stellen interne Zitzenversiegler zum Schutz vor Neuinfektionen insbesondere auf ökologischen Betrieben eine Alternative zur antibiotischen Trockenstelltherapie dar (Schaeren und Maurer, 2005). Hauptinhaltsstoff der zur Zeit auf dem Markt verfügbaren internen Zitzenversieglerpräparate ist Bismuthsubnitrat (Bayer, 2016; Zoetis, 2016). Da es sich bei Bismuthsubnitrat um ein Schwermetallsalz handelt, ist der Einsatz interner Zitzenversiegler auf ökologischen Betrieben jedoch wegen möglicher Umwelt- und Gesundheitsrisiken - das Kalb saugt oft die erste Milch beim Muttertier und könnte so Reste des Versieglers aufnehmen - nicht vollständig unumstritten (Notz, 2005).
Das Ziel dieser Arbeit war es, auf ökologischen Betrieben Konzepte zur Verbesserung der Eutergesundheit während der Trockenstehphase gemäß dem Grundsatz der Ausheilung bestehender sowie der Verhinderung neuer Infektionen zu finden. In einem ersten Versuch wurde dazu eine Entscheidungshilfe für den Einsatz antibiotischer Trockensteller entwickelt, um die Heilungsrate während der Trockenstehphase bei minimalen Arzneimitteleinsatz zu erhöhen. In einem zweiten
Versuch wurde ein neuartiger Prototyp eines Schwermetall-freien internen Zitzenversieglers zur Senkung der Neuinfektionsrate getestet. Aus beiden Feldversuchen ging jeweils eine Publikation hervor. Im ersten Versuch wurden Daten zu trockenzustellenden Tieren, zur angewandten Therapie und zum bakteriologischen Status vor und nach dem Trockenstellen erfasst und ausgewertet und auf Basis der Ergebnisse die Entscheidungshilfe zur Trockenstelltherapie erstellt. Dabei wurde das auf den Betrieben bestehende Trockenstellverfahren während der Versuchslaufzeit nicht beeinflusst und hinterher mit der ermittelten Methode verglichen. Die Ergebnisse dieser Studie können letztendlich auch als Grundlage für die Einführung eines selektiven Trockenstellverfahrens auf konventionellen Betrieben zur Minimierung des Antibiotikaverbrauchs dienen. In dem zweiten Versuch wurden Euterviertel von Versuchstieren mit dem Bismuthsubnitrat-freien internen Zitzenversiegler behandelt und die Neuinfektionsrate mit unbehandelten Vierteln verglichen.
2. Publikation I: Selection of cows for treatment at dry-off on organic dairy farms
(Selektion von Kühen für die Behandlung zum Trockenstellen auf ökologisch wirtschaftenden Milchviehbetrieben)
Klemens Kiesner1, 2, Nicole Wente1, Otto Volling3, Volker Krömker1, 2
1 Fakultät II, Abteilung für Bioverfahrenstechnik – Mikrobiologie, Hochschule Hannover
2 Klinik für Rinder, Stiftung Tierärztliche Hochschule Hannover
3 Bioland e.V.
Journal of Dairy Research 2016; 83: 1-8
Eingereicht: 8.5.2016 Akzeptiert: 6.10.2016
© Proprietors of Journal of Dairy Research 2016 doi: 10.1017/S0022029916000662
2.1 Zusammenfassung
Auf Grund von Einschränkungen bei der Benutzung antibiotischer Trockensteller muss auf ökologisch wirtschaftenden Betrieben selektives Trockenstellen angewendet werden. Dies erfordert geeignete Methoden zur Identifikation infizierter Tiere zum Zeitpunkt des Trockenstellens. Das Ziel dieser Studie war die Erstellung einer Entscheidungshilfe für den Einsatz antibiotischer Trockensteller basierend auf Kuhfaktoren, die Einfluss haben auf den Infektionsstatus zum Trockenstellen, sowie die Heilungs- und Neuinfektionswahrscheinlichkeit während der Trockenstehphase.
Dazu wurden Daten von 250 Kühen von fünf ökologischen Betrieben gesammelt.
Darunter waren die somatischen Zellgehalte aus den Berichten der Milchleistungsprüfung, Ergebnisse des California Mastitis Tests (Schalmtest) zum Zeitpunkt des Trockenstellens, Fälle klinischer Mastitis während der Laktation, Alter, sowie angewandte Trockenstelltherapie. Eine vorhandene Infektion zum Trockenstellen wurde am genausten mit Hilfe der somatischen Zellgehalte der letzten drei Milchleistungsprüfungen vor dem Trockenstellen und einem Grenzwert von 100.000 somatische Zellen/ml (geometrisches Mittel) identifiziert. Die Berücksichtigung entweder von Fällen klinischer Mastitis, Ergebnissen des California Mastitis Tests und dem Alter der Kuh führte zu einem geringen Anstieg in der Sensitivität. Die Heilungswahrscheinlichkeit während der Trockenstehphase stieg mit dem Einsatz antibiotischer Trockensteller und interner Zitzenversiegler und sank bei einer Dauer der Trockenstehphase von über 56 Tagen. Das Risiko einer Neuinfektion sank mit dem Einsatz interner Zitzenversiegler und bei Vorhandensein einer Infektion mit Minor Pathogens zum Zeitpunkt des Trockenstellens. Verglichen mit der Selektion, die durch die Betriebsleiter während der Studienzeit selbst durchgeführt wurde, erzielten Selektionskriterien mit einem fest definierten Grenzwert eine höhere Sensitivität.
2.2 Abstract
Restrictions regarding the use of antibiotics make selective antibiotic dry cow therapy (DCT) mandatory on organic farms in Germany. This requires methods for identifying cows with an intramammary infection (IMI) at dry-off. The aim of this field study was to create a decision scheme for the use of DCT based on cow level factors associated with IMI at dry-off and the probability of both cure and new infection (NI) during the dry period. Data from 250 cows from five organic farms were collected including somatic cell counts (SCC) from Dairy Herd Improvement (DHI) records, California mastitis test (CMT) results at dry-off, clinical mastitis (CM) history, parity and dry-off treatment. IMI at dry-off were most accurate identified using a geometric mean SCC of 100,000 cells/mL as a threshold at either one or three DHI records prior to dry- off. Using a combination of SCC with either CM history, CMT at dry off or parity slightly increased the sensitivity of detection (SE). The probability of cure of the infection over the dry period increased with use of both antibiotic DCT and application of an internal teat sealant (ITS) and decreased when the dry period was longer than 56 days. The risk of NI decreased with the use of ITS and infections with minor pathogens at dry-off.
Compared with the selection performed by the farmers during the study period identification of IMI based on the selection criterion with a defined SCC threshold achieved a higher SE.
Keywords: selective dry cow therapy, organic farming, infection at dry-off, somatic cell count
2.3 Introduction
A key component of dry cow mastitis management is the use of antibiotic dry cow therapy (DCT). DCT essentially has two functions, the elimination of existing intramammary infections (IMI) at dry-off and the prevention of new IMI during the dry period (Bradley & Green, 2004). DCT has been shown to achieve a 1.78 times higher cure rate compared with self-cure in untreated quarters (Halasa et al., 2009). In year 2013, 80 % of cows received antibiotic DCT in Germany (Wallman, 2014).
According to the guidelines of organic farming the use of DCT has to be restricted (European Commission, 2008). It should be applied only to “single problematic animals if indicated medically and with proof of agent” (Bioland Standards, 2015). However, there are no alternative strategies and therapies to reduce IMI during the dry period.
Therefore, on organic farms at calving the mastitis prevalence is high due to low cure and a high new infection rates (NIR) and contagious pathogens are predominant (Hayton & Bradley, 2004).
Even if selective DCT is mandatorily performed, infected cows should not be left untreated (Berry & Hillerton, 2002a; Berry et al., 2004). Thus the criteria for accurately identifying infected cows to receive treatment at dry-off need to be improved to enhance the accuracy of the selective DCT (Huxley et al., 2002; Robert et al., 2008).
Logistic and financial considerations involved in sampling and examining milk from all cows usually make this selection method impractical (Eberhart, 1986; Sargeant et al., 2001). The most commonly used selection method is based on the monthly recorded cow somatic cell counts (SCC) (Bradley & Green, 2004; Torres et al., 2008; Biggs et al., 2016).
Furthermore, the California mastitis test (CMT) at dry-off and the clinical mastitis (CM) history of the cow are mentioned as selection tools (Sanford et al., 2006; Torres et al., 2008).
Even if infected cows are identified correctly, several factors influence the probability of cure in treated cows and animals with low healing prospects should rather be recommended for culling (Osteras, 2006). However, as a long lifespan is an objective on organic farms, improvement of the overall udder health by culling has limited application. Therefore, prevention of new infections (NI) is of particular importance.
The application of internal teat sealants (ITS) at dry-off is one opportunity to effectively protect cows from NI (Rabiee & Lean, 2013).
The aim of the present study was to create a decision scheme for the use of DCT on organic dairy farms based on cow level factors, which were evaluated for identifying infected cows at dry-off and for their influence on the probability of cure of existing infections and prevention of NI during the dry period.
2.4 Material and methods
2.4.1 Farms and cows
The field study was carried out on five organic dairy farms in Lower Saxony, Germany. Herd size ranged from 71 to 175 lactating German Holstein cows. Milk yield per cow and year varied between 6500 and 9890 kg (mean 8402 ± 1544 kg). The mean intercalving interval was 399 ± 19 d. Bulk tank somatic cell count at the beginning of the study ranged from 197,000 to 289,000 cells/ml. On four farms cows were milked twice a day in a milking parlour, one farm used an automatic milking system. Dry cows were either kept on pasture for the whole dry period or had continuous access to it.
The 250 cows that had finished their first or subsequent lactation and had been dried off between 13 June and 30 October 2014 were recruited for the study.
2.4.2 Dry cow therapy and data collection
During the study period no attempt was made to influence the dry cow management on the farms. All farms performed selective DCT. Dry cow products containing either cloxacillin, cefquinom, a combination of benzyl penicillin, dihydrostrepromycin and nafcillin or a combination of benethamin penicillin, penthamathydroiodid and framycetin were used. The date of dry-off was scheduled based on the expected calving date. None of the farms used a strict selection and treatment policy at dry-off.
The selection of cows for antibiotic DCT was primarily based on DHI SCC records. An average SCC > 200,000 and > 250,000 cells/mL in lactation were stated as thresholds for the application of antibiotic DCT by the farmers. Four farms also included cases of CM during the previous lactation in their decision making. An ITS containing bismuth subnitrate was used on four farms and either applied to all animals (two farms) or only
to those that did not received antibiotic treatment (two farms). One farm did not use ITS at all. DCT was administered by the farmers using a hygienic procedure immediately after the last milking.
Cow information was obtained from DHI records. Parity, date of calving, milk yield and SCC were collected. Cases of CM in the previous lactation and milk yield at dry- off were obtained directly from farm records. On two farms the milk yield at dry-off was calculated from the previous DHI record.
At dry-off, all cows had a CMT performed by the first author on each functional quarter. The CMT reaction of each quarter was recorded as 0 indicating no reaction and ranging to 3, a strong positive reaction (Sargeant et al., 2001).
After calving, animals were examined by the farm staff for signs of CM until 100 d in milk (DIM).
2.4.3 Sampling and laboratory procedures
Quarter foremilk samples were collected aseptically by one of the authors at three points in time according to National Mastitis Council (NMC) guidelines as cited by the German Veterinary Association (GVA, 2009): At dry-off, within 5 to 12 DIM (C1) and 7 d later (C2). Sampling on a farm was usually on the same day and at the same time of day each week. Milk samples in tubes containing Ly 20 (boric acid and methylene blue) were transported in a cool box to the microbiological laboratory at the University of Applied Sciences, Hannover and were usually assayed within 24 h after arrival.
Otherwise, samples were stored at 8°C for no more than 2 d before assay. Milk samples were cultured according to the NMC and GVA recommendations (GVA, 2009).
2.4.4 Definitions
The two most numerous types of colony on a plate were identified. A milk sample was bacteriologically positive if ≥ 100 colony forming units (cfu)/mL of a major contagious pathogen (Staphylococcus (S.) aureus, Streptococcus (Sc) agalactiae, Sc.
dysgalactiae and Trueperella (T.) pyogenes) or ≥ 500 cfu/ml of any other pathogen were isolated. A quarter was considered infected at dry-off based on a single sample.
After calving, a quarter was considered infected if the same pathogen was isolated from both samples (C1 and C2). Bacteriological cure was defined as a pathogen present at dry-off which was not cultured after calving. Quarters were termed “newly infected” if they had positive results for a pathogen not been isolated at dry-off. A cow was considered infected if at least one quarter was infected. If all infected quarters within a cow at dry-off were cured, at least one quarter had a NI during the dry period or showed signs of CM within 100 DIM, the cow was termed “cured”, “newly infected”
or “affected by CM”, respectively.
2.4.5 Data analysis
Analyses were performed at cow level using Excel 2010 (Microsoft Corporation) and SPSS (SPSS 23.0, Chicago; USA). Differences in cure rate and NIR between treatment groups (untreated, antibiotic DCT, ITS) were analysed using chi2-analysis.
Probabilities of cure, NI and CM within 100 DIM were analysed using backward stepwise regression analysis. Predicting variables were: treatment group, teat disinfection at dry-off, type of pathogen present at dry-off, parity, milk yield at dry-off, CM during lactation, CMT at dry-off, lactation period length, dry period length and mean SCC during lactation. Statistical significance was assumed at P ≤ 0.05. Nonsignificant variables were excluded from the final model. If predictors showed strong correlations with each other (r > 0.8), the predictor with the highest significance was kept in the final model. As clustering was present in the study design a generalised estimating equation (GEE) model was used with those main effects included in the final logistic model. A random cow in herd effect was included in the model. Finally, odds ratio (OR) with 95
% confidence intervals (CI) were calculated.
For the analysis of selection criteria for infected cows at dry-off the target parameter (infected or infected with certain pathogen) was determined based on the final regression model for cure. Results of the bacteriological analysis served as the gold standard. For SCC as selection criterion the optimal threshold and the optimal number of DHI records (one month prior to dry-off, three months, all records) were evaluated.
When considering more than one DHI record the geometric mean SCC was used.
Receiver operating characteristic (ROC) curves were created and sensitivity (SE) and
specificity (SP) were calculated. Accuracy (number of true positives and true negatives/ total number of samples), positive predictive value (PPV) and negative predictive value (NPV) were also calculated. PPV and NPV were estimated in relation to prevalence ranging from 0 to 100%. CM history, parity and CMT as selection criteria were tested alone and in combination with SCC. All selection criteria were also evaluated with the purpose of identifying only cows infected with agents other than minor pathogens (i.e. coryneforms and coagulase-negative staphylococci (CNS)). In a GEE model all selection criteria were tested as fixed effects for their influence on the probability of IMI at dry-off (for rules for statistical significance, correlation and random effects see above).
2.5 Results
Overall prevalence of IMI at dry-off based on the pooled data was 85.6 % of cows.
The most common bacteria at dry-off and after calving were CNS and coryneforms, followed by S. aureus. Table 1 shows the distribution of pathogens. Excluding IMI caused by minor pathogens 96 of 250 cows were infected at dry-off (38.4 %). The prevalence after calving was 58.0 % and 14.4 %, respectively.
2.5.1 Identifying infected cows at dry-off
To determine a selection criterion for identifying infected cows at dry-off, the SCC threshold of 100,000 cells/mL was closest to the optimal cut-off values on the ROC curves if SE and SP were weighted equally (maximum sum of SE and SP) (Figure 1).
As expected, SP increased using 200,000 cells/mL as the threshold but both SE and accuracy decreased. Selection based on SCC from all DHI records during lactation was least accurate (data not shown). The accuracy was almost identical using only the most current DHI record or the three last consecutive records prior to dry-off, having a higher SE in the first and a higher SP in the second case (73.6 % and 72.0 %, respectively).
Table 1. Distribution of pathogens isolated from quarter milk samples from 250 cows at dry off and post partum on five organic farms. Results are presented in percentages of cows infected with a particular organism.†
†A cow was classified as infected if at least one quarter was infected; however, she could be infected with more than one pathogen if she had more than one quarter infected with different organisms and/or if she had mixed infections
‡Based on paired samples
Bacteriological result At dry-off post partum‡
n % n %
No growth 36 14.4 105 42.0
Coagulase-negative staphylococci 118 47.2 83 33.2
Staphylococcus aureus 53 21.2 17 6.8
Streptococcus dysgalactiae 6 2.4 3 1.2
Streptococcus uberis 15 6.0 7 2.8
Coliforms/ Escherichia coli 5 2.0 2 0.8
Coryneforms 130 52.0 61 24.4
Enterococci 19 7.6 5 2.0
Streptococcus canis 6 2.4 4 1.6
Other 9 3.6 2 0.8
Figure 1. Criteria receiver operating characteristic (ROC) curves for identifying cows with an intramammary infection (IMI) at dry-off, based on somatic cell counts (SCC) of either the last dairy herd improvement (DHI) record (---) or three consecutive records (—) prior to dry-off. Optimal SCC cut-off values (○) giving equal weight to sensitivity and specificity and SCC thresholds of 100,000 cells/ml (●, ♦) are marked. Diagonal line for a test without benefit is shown for comparison.
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
Sensitivity
1 - Specificity
Figure 2. Positive predictive values (PPV) and negative predictive values (NPV) for geometric mean somatic cell count (SCC) for the last three consecutive records prior to dry-off as selection criterion for infected cows in relation to the prevalence. SCC threshold is set at 100,000 cells/ml (100) and 200,000 cells/ml (200).
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1
Predictive value
Prevalence
PPV 100 NPV 100
PPV 200 NPV 200
The PPV and NPV for SCC cut-offs at 100,000 and 200,000 cells/mL in relationship to all possible prevalences of IMI at dry-off are shown in Figure 2. Overall, and especially at lower prevalences, the threshold of 200,000 cells/mL led to a higher probability that a cow classified as infected was indeed infected (PPV 97.3 % at prevalence of 85.6 %). In comparison, the probability that a cow classified as uninfected had no IMI was higher using 100,000 cells/mL as threshold and three consecutive DHI records prior to dry-off (NPV 31.5 %). The NPV for using only one DHI record was almost similar (32.4%). At higher prevalence, the lower threshold performed better as the NPV was higher and the difference in PPV between both thresholds became smaller. The calculated values for SE, SP, accuracy, PPV and NPV are shown in Table 2.
Parity as the selection criterion had the highest accuracy (52.8 %) besides SCC with an SE of 49.5 % and SP of 72.2 %. Using CMT at dry-off, accuracy was 43.5 %, SE 40.1 % and SP 36.1 %. CM history as the selection criterion had the lowest accuracy (26.8 %). Adding these factors to the SCC-based selection method led to a slight improvement in accuracy and SE and a varying decrease in SP. The combination of SCC and parity showed the highest accuracy, SE and NPV (Table 2).
Excluding cows only infected by minor pathogens the 100,000 cells/mL threshold was closer to the optimal SCC cut-off on the ROC curve than the higher threshold of 200,000 cells/mL (data not shown). Accuracy increased with the number of DHI records used. When considering all records, SE (65.6 %), SP (67.5 %), accuracy (67.0
%) and PPV (55.8 %) were lower than for identification of all pathogens, whereas NPV (76.0 %) was higher. The curve progression of predictive values in relation to prevalence was similar to the progression for all infections (data not shown). CM history, parity and CMT as selection criteria performed better than for the identification of all infections and had an average accuracy of 61.8%. The results for SE and SP were: CM 20.8 % and 86.4 %; CMT 51.6 % and 68.0 %; parity 59.3 % and 61.7 %.
Adding these factors to the SCC based selection method led to a slight decrease in accuracy (minus 4%). Combinations of SCC with either CM history or CMT had similar accuracy. Regarding SE and NPV the combination of SCC and CMT achieved the best results (SE: 82.3 %; NPV: 82.5 %).
Table 2. Sensitivity (SE), specificity (SP), accuracy, positive (PPV) and negative predictive values (NPV) for identifying cows with an intramammary infection (IMI) at dry-off using somatic cell counts with threshold 100,000 cells/mL (SCC 100) or 200,000 cells/mL (SCC 200) and three consecutive Dairy Herd Improvement (DHI) records prior to dry-off. Effect of adding information on clinical mastitis (CM) history, parity and California mastitis test (CMT) results at dry-off as selection criteria. Evaluation of the selection performed by the farmers during the study period is shown for comparison.
Selection
criterion SE % SP % Accuracy % PPV % NPV % Prevalence %
SCC 200† 34.1 (27.8-
40.5) ‡ 94.4 (87.0-
100) ‡ 42.8 97.3 19.0
85.6 SCC 100† 70.5 (64.5-
76.7) ‡
80.5 (67.6-
93.4) ‡ 72.0 95.6 31.5
+ CM§ 72.9 (66.9-
78.9) ‡ 78.0 (64.2-
91.3) ‡ 74.0 95.1 32.6
+ parity§ 78.5 (73.0-
84.0) ‡ 61.0 (45.2-
77.0) ‡ 76.0 92.3 32.4
+ CMT§ 78.5 (73.0- 84.0) ‡
50.0 (33.6-
66.3) ‡ 74.4 90.3 28.1
Selection by farmers ¶
36.3 (4.0-
69.4) †† 91.6 (75.0-
100) †† 43.7 (21.0-
70.9) †† 96.7 (86.6-
100) †† 20.0 (8.0-
31.5) †† 85.8 (76.4- 93.1) ††
† All cows with a geometric mean SCC > either 100,000 or 200,000 cells/mL for three consecutive DHI records prior to dry-off are considered as infected
‡ 95% Confidence intervals
§ All cows with an SCC of > 100,000 cells/ml or with ≤ 100,000 cells/ml but with CM during previous lactation/ parity >2 / at least one quarter with CMT >1 were considered as infected
¶ No strict selection policy at dry-off; for further information see “Material and methods”
†† Mean of the five farms (min. – max.)
The final GEE model showed that a geometric mean SCC > 100,000 cells/mL for three consecutive DHI records prior to dry-off is significantly associated with the probability IMI at dry-off (OR: 15.425; 95 % CI: 5.670 – 41.930, P ≤ 0.001). A random cow in herd effect was not significant in this or any other model.
Compared with using SCC as selection criterion and 100,000 cells/mL as threshold, the SE for identifying/treating infected cows of the selection procedure performed by the farmers was low and varied strongly between the farms (Table 2). The prevalence of IMI at dry-off on the farms ranged from 76.4 % to 93.1 %. SP and PPV were high on all farms, whereas NPV was low. Excluding infections caused by minor pathogens the mean prevalence of IMI at dry-off on the farms amounted to 37.9 %. In this case, accuracy (63.2 %), SE (46.0 %) and NPV (70.0 %) of the farmers’ selection procedure were higher and SP (74.4 %) and PPV (51.4 %) lower.
2.5.2 Cure rates and clinical mastitis
The overall cure rate during the dry period was 67.8 % (Table 3). Cows receiving antibiotic DCT had a significantly higher cure rate than those no treated with antibiotic DCT (P ≤ 0.001). In both groups, cows receiving an internal teat sealant had significantly higher cure rates than unsealed cows (P ≤ 0.001).
In the final GEE model antibiotic DCT (OR: 8.015; 95 % CI: 2.450 – 26.223; P ≤ 0.001), application of an ITS (OR: 7.352; 95 % CI: 1.816 - 29.762; P ≤ 0.01) and a dry period length > 56 days (OR: 0.420; 95 % CI: 0.209 – 0.845; P ≤ 0.05) were significantly associated with the probability of cure. There was no effect on cure whether the infection at dry-off was caused by minor pathogens, S. aureus, streptococci or other pathogens.
Within 100 DIM, 41 cases of clinical mastitis were detected. Of the affected cows 24.4 % were bacteriologically negative after calving, 43.9% were infected with CNS, 31.7% with coryneforms, 14.6 % with S. aureus, 4.9 % with S. dysgalactiae, 4.9 % with S. canis, and 2.4 % with S. uberis, enterococci and others, respectively. In the final GEE model the probability of CM within 100 DIM was associated with antibiotic DCT (OR: 2.422; 95 % CI: 1.116 – 5.256; P ≤ 0.05) and a negative culture result after calving (OR: 0.398; 95 % CI: 0.178 – 0.892; P ≤ 0.05).
Table 3. Cure and new infection rate in the different treatment groups: With/without antibiotic dry cow therapy (DCT) and with/without internal teat sealant (ITS).
a, b significant difference between cows receiving antibiotic DCT and those receiving no antibiotic (P ≤ 0.001)
c, d significant difference between cows receiving ITS and unsealed ones (P ≤ 0.001)
e, f significant difference between cows only treated with ITS compared with those treated only with antibiotic DCT (P ≤ 0.001)
2.5.3 New infection rates
The overall NIR was 44.0 % of cows (Table 3). The NIR in the cows receiving antibiotic DCT (with/without ITS) was significantly lower compared with the group receiving no antibiotic DCT (P ≤ 0.001). In both groups cows receiving an ITS had a significantly lower NIR than those unsealed (P ≤ 0.001). When comparing solely application of ITS and solely antibiotic DCT, the NIR was significantly lower in sealed cows (P ≤ 0.001). The GEE model showed that application of an ITS is significantly associated with the risk of NI (OR: 0.407; 95 % CI: 0.210 – 0.790; P ≤ 0.01). Antibiotic DCT had no significant effect in the final model. An infection with minor pathogens present at dry-off was significantly associated with the risk of NI (OR: 0.479; 95 % CI:
0.257 – 0.893; P ≤ 0.05). Disregarding NI by minor pathogens, only CNS infections at dry-off showed this effect (OR 0.377, 95 % CI 0.147 to 0.963; P ≤ 0.05).
Treatment Cure rate % New infection rate %
No antibiotic DCT 59.2a 46.7a
No ITS 55.4c 50.9c
ITS 65.5d 40.0d, e
Antibiotic DCT 86.6b 37.1b
No ITS 66.7c 61.5c, f
ITS 97.7d 22.7d
Overall 67.8 44.0
2.5.4 Decision scheme
Figure 3 shows the final decision scheme for the application of antibiotic DCT and ITS. Cows with a geometric mean SCC above 100,000 cells/mL for three consecutive DHI records prior to dry-off are considered as infected and should be treated with antibiotic DCT. Cows classified as uninfected by one or more selection criteria can be left untreated or receive an ITS depending on the risk of NI.
Figure 3. Decision scheme for the application of antibiotic dry cow therapy (DCT) and/or an internal teat sealant (ITS) at dry-off.
a Geometric mean for three months prior to dry-off
b Prevalence 85.6%
c California mastitis test (CMT), Clinical mastitis during lactation, older cows
d Geometric mean SCC > 600-700000 cells/mL for three consecutive records prior to dry-off (Osteras, 2006)
Drying off
SCC above 100,000 cells/ml?a
YES
Probability of infection > 95%b
In additional test (e.g.
CMT) positive?c
Antibiotic DCT (+ ITS) Low cure
prospects ?d
NO
Internal teat sealant YES
NO
Culling
YES
NO
High new infection rate?
YES
No treatment NO
2.6 Discussion
The present study was performed with no attempt to influence the current dry cow management on the farms, no preselecting or clustering of trial animals. This approach enabled evaluation of realistic farm conditions. Only organic farms were selected for the trial.
Analysis of DCT at cow rather than at quarter level was adopted for practical and biological reasons (Barkema et al., 1997).
The prevalence of infection at dry-off was high (81.2 %). Minor pathogens were most frequently isolated. The relatively high rate of infections by S. aureus compared with S. uberis and enterobacteriacae indicates that contagious predominate over environmental pathogens. A similar pattern was reported for organic farms previously (Hayton & Bradley, 2004).
2.6.1 Identifying infected cows
Bacteriological culture is commonly used as the reference test for infection status when evaluating diagnostic tests (Sargeant et al., 2001; Sanford et al., 2006; Torres et al., 2008).
Like in previous studies SCC was confirmed as an adequate tool to identify infected cows at dry-off. The SE of SCC as a selection criterion in the present study was similar to values reported by Pantoja et al. (2009) and Torres et al. (2008). The SP was distinctively higher than in the other studies (80.5 % vs. 63.0 %).
The optimal SCC threshold of 100,000 cells/mL in the present study is consistent with the study by Pantoja et al. (2009) that achieved balanced SE and SP with the same threshold. Others found 200,000 cells/ml to be a sensible threshold for IMI (Bradley & Green, 2004; Torres et al., 2008). Differences in thresholds can be explained by the overall high prevalence in the present study (Biggs et al., 2016).
Furthermore, infections caused by minor pathogens normally induce less intense SCC responses in milk (Sargeant et al., 2001; Pantoja et al., 2009).
Excluding infections by minor pathogens at dry-off the SE of SCC as the selection criterion was increased. A similar increase in SE has been observed in other studies
when detection of all pathogens was compared with detection of major pathogens only (Sanford et al., 2006; Torres et al., 2008).
In terms of the number of DHI records used to identify IMI the three last records prior to dry-off were recommended (Torres et al., 2008; Biggs et al., 2016). In the present study, the accuracy of SCC to identify all infected cows was almost similar using results of one or three DHI records prior to dry-off but decreased using all records of the previous lactation. However, cows infected with major pathogens were identified most accurately when all records were considered.
The predictive values change with the prevalence of infection in the population and the test characteristics. Prevalence and accordingly PPV in the present study were distinctively higher than in the studies reported by Pantoja et al. (2009) and Torres et al. (2009) with reported prevalence about 34.5 % and a PPV of 47.0 % and 40.4 %, respectively. In contrast, the NPV was lower (31.5 % vs. 76.0 - 80.9 %). However, with an assumed prevalence below 20 %, the NPV was 91 %, similar to the results of Torres et al. (2009).
Sanford et al. (2006) suggested that screening cows for selective DCT with CMT at dry-off is reasonable, but mostly on herds with a low prevalence of infection. Estimates of SE and SP in the present study, when using CMT as the only selection criterion, were lower than the values of 70 % and 48 % reported by Sanford et al. (2006). Similar to other studies, CMT performed better when excluding infections by minor pathogens (Sargeant et al., 2001; Sanford et al., 2006).
The occurrence of CM in the previous lactation had no influence on the probability of IMI at dry-off and selecting only cows with CM for antibiotic DCT had a low SE.
However, as other studies showed that cows with CM are at a higher risk for infections with major pathogens general selection for antibiotic DCT may make sense (Zadoks et al., 2001; Bradley & Green, 2004).
Since the prevalence of IMI and pathogens differ between farms, the utility of any selection criterion depends on individual farm conditions. A high prevalence of infections at dry-off requires a selection criterion with a high SE to minimise the number of false negatives (Biggs et al., 2016). This applies particularly to contagious pathogens such as S. aureus as leaving infected cows untreated is undesirable for
eradication (Huxley et al., 2002). If limited use of antibiotics is the goal, as on organic farms, and minor pathogens or pathogens ubiquitous in the environment are most prevalent, the use of a selection criterion that provides optimal accuracy is a reasonable approach (Torres et al., 2008). The same approach and the same selection criteria as described in this study could be used to implement selective DCT on conventional farms in order to reduce drug usage. The optimal SCC threshold might be higher as selective DCT is advisable for conventional farms with low prevalence of IMI (Sanford et al., 2006).
To improve the selection process a combination of selection criteria can be used to increase the NPV. It would be conceivable to implement a second diagnostic test on animals classified as uninfected by SCC in the first step. Performing additional diagnostic tests such as bacteriological culture on “problematic” animals with a high SCC and so already classified as infected to minimise the number of false positives is questionable since erroneously treated cows do not adversely influence the herd`s udder health status, whereas false negatives do.
Compared with the non-strict DCT policy applied on the trial farms, the use of selection criteria with defined thresholds enabled identification of infected cows with a higher SE. The fact, that there were also large differences in the SE of the selection procedure between the farms in spite of having almost the same prevalence indicates potential for further optimisation (Krömker & Volling, 2007).
It is important to note that, in comparison with selection by the farmers, the implementation of the selection criteria would approximately double the use of antibiotics. However, the percentage of erroneously treated animals would be unchanged.
2.6.2 Cure, new infections and clinical mastitis
The overall cure rate in the present study was high compared with the average at cow level of 46 % ± 12 % on organic farms (Krömker & Volling, 2007). As expected, cows receiving antibiotic DCT had a higher probability of cure (Halasa et al., 2009).
Although such effects could not be shown in the present study, certain animal characteristics are reported to significantly decrease prospects of cure after DCT.
Therefore, it can be reasonable that cows with at least one case of clinical mastitis and SCC above 600,000 - 700,000 cells/mL in the three consecutive records prior to dry- off are considered for culling as the risk of treatment failure is high (Osteras, 2006).
Cows receiving ITS had a higher cure rate compared with unsealed cows, either in combination with or without antibiotic DCT. The same effect has been reported previously (Newton et al., 2008). Even though the differences in cure rates were not significant in the named study, they suggest that reinfections with the same pathogen during the dry period are important and could lead to an apparently lower cure rate in unsealed cows.
IMI after calving increased the risk of CM within 100 DM as reported previously (Green et al., 2002).
The NIR was high during the dry period, as reported previously for organic farms.
Conventional farms using DCT appropriately had a 20 % lower NIR (Krömker & Volling, 2007). Cows with an infection caused by a minor pathogen at dry-off had a lower risk of a NI during the dry period. The effect of infections with minor pathogens at dry-off is controversial, as it has been demonstrated that such quarters are significantly less likely to become infected with major pathogens (Huxley et al. 2003).In contrast, others found that minor pathogen-positive quarters are significantly more likely to become infected with environmental streptococci and coliforms (Hogan et al., 1988; Berry &
Hillerton, 2002b). Application of ITS at dry-off provided efficient protection against NI, similar to the results of a meta-analysis evaluating the effect of sealing (Rabiee & Lean, 2013). As reported previously, cows receiving only ITS had significantly fewer NI compared with those treated only with antibiotic DCT (Huxley et al., 2002). Therefore, in cows classified as uninfected, application of ITS is preferably compared with prophylactic use of antibiotics. A lower NIR during the dry period will lead to an overall improvement of the udder health status in the herd (as well as a lower prospective prevalence) and better future results of any selection criterion.
2.7 Conclusion
The present study showed that the use of a selection criterion with a defined threshold may enable identification of infected cows with a higher SE compared with a non-strict DCT policy. Any selection criterion needs to be adapted for on-farm conditions and goals. In herds with a high prevalence of infection, caution should be taken about the use of selection criteria or selective DCT programmes should probably not be considered at all. If selective DCT is mandatory, as on organic farms, and prevalence of IMI high, the farmer and veterinarian need to take into account that the use of any selection criterion implies the probability of false negative cows and that the udder health status may not improve. Besides the use of antibiotic DCT the overall udder health status can be improved by reducing the number of NI during the dry period by using less controversial and less restricted methods like ITS and improvement of housing conditions.
The authors thank the dairy farmers who participated in the study. The study was financially supported by the Ministry of Food, Agriculture and Consumer Protection of Lower Saxony, Germany. The authors declare no potential conflicts of interest.
2.8 References
Barkema HW, Schukken YH, Lam TJ, Galligan DT, Beiboer ML & Brand A 1997 Estimation of interdependence among quarters of the bovine udder with subclinical mastitis and implications for analysis. Journal of Dairy Science 80 1592–1599 Berry EA & Hillerton JE 2002a The effect of selective dry cow treatment on new
intramammary infections. Journal of Dairy Science 85 112–121
Berry EA & Hillerton JE 2002b The effect of an intramammary teat seal on new intramammary infections. Journal of Dairy Science 85 2512–2520
Berry EA, Hogeveen H & Hillerton JE 2004 Decision tree analysis to evaluate dry cow strategies under UK conditions. Journal of Dairy Research 71 409–418
Biggs A, Barret D, Bradley A, Green M, Reyher K & Zadocks R 2016 Antibiotic dry cow therapy: where next? Veterinary Record 178 93–94
Bioland 2015 Bioland standards. Mainz, Germany: Bioland
Bradley AJ & Green MJ 2004 The importance of the nonlactating period in the epidemiology of intramammary infection and strategies for prevention. Veterinary Clinics Food Animal Practice 20 547–668
Eberhart RJ 1986 Management of dry cows to reduce mastitis. Journal of Dairy Science 69 1721–32
European Commission 2008 COMMISSION REGULATION (EC) No 859/2008 Official Journal of the European Union L250 1-84.
German Veterinary Association 2009 Leitlinien zur Entnahme von Milchproben unter antiseptischen Bedingungen und Isolierung und Identifizierung von Mastitiserregern [Guidelines for aseptic milk sampling and guidelines to isolate and identify mastitis pathogens]. 2nd edition. Gießen, Germany: German Veterinary Association
Green MJ, Green LE, Medley GF, Schukken YH & Bradley AJ 2002 Influence of dry period bacterial intramammary infection on clinical mastitis in dairy cows. Journal of Dairy Science 85 2589–2599
Halasa T,Nielen M,Whist AC & Osteras O 2009 Meta-analysis of dry cow management for dairy cattle. Part 2. Cure of existing intramammary infections.
Journal of Dairy Science 92 3150–3157
Hayton AJ & Bradley A 2004 The control of mastitis on organic units. In Proceedings of the British Mastitis Conference, Stoneleigh, pp. 27–36.
Hogan JS, Smith KL, Todhunter DA & Schoenberger PS 1988 Rate of environmental mastitis in quarters infected with Corynebacterium bovis and staphylococcus species. Journal of Dairy Science 71 2520–2525
Huxley JN, MJ Green & Bradley AJ 2003 Corynebacterium bovis - friend or foe? In Proceedings of the British Mastitis Conference, Garstang, pp. 23–34
Huxley JN, Green MJ, Green LE & Bradley AJ 2002. Evaluation of the efficacy of an internal teat sealer during the dry period. Journal of Dairy Science 85 551–561 Krömker V & Volling O 2007 Therapeutisches Eutergesundheitsmanagment in
Milchviehbetrieben des ökologischen Landbaus [Therapeutic udder heatlth management in organic dairy farms]. In Proceedings 9. Wissenschaftstagung Ökologischer Landbau, Stuttgart, Germany, pp. 3–6
Newton HAT, Green MJ, Benchaoui H, Cracknell V, Rowan T & Bradley AJ 2008 Comparison of the efficacy of cloxacillin alone and cloxacillin combined with an internal teat sealant for dry-cow therapy. The Veterinary Record 162 678-684 Osteras O 2006 Mastitis epidemiology, practical approaches and applications. In
Proceedings 24. World Buiatrics Congress, Nice, France
Pantoja JC, Hulland C & Ruegg PL 2009 Dynamics of somatic cell counts and intramammary infections across the dry period. Preventive Veterinary Medicine 90 43–54
Rabiee AR & Lean IJ 2013 The effect of internal teat sealant products (Teatseal and Orbeseal) on intramammary infection, clinical mastitis, and somatic cell counts in lactating dairy cows: a meta-analysis. Journal of Dairy Science 96 6915–31
Robert A, Roussel P, Bareille N, Ribaud D, Sérieys F, Heuchel V& Seegers H 2008 Risk factors for new intramammary infections during the dry period in untreated dairy cows from herds using selective dry cow therapy. Animal 2 247–254
Sanford CJ, Keefe GP, Sanchez J, Dingwell RT, Barkema HW, Leslie KE & Dohoo IR 2006 Test characteristics from latent-class models of the California mastitis test.
Preventive Veterinary Medicine 77 96–108
Sargeant JM, Leslie KE, Shirley JE, Pulkrabek BJ & Lim GH 2001 Sensitivity and Specificity of Somatic Cell Count and California mastitis test for identifying intramammary infection in early lactation. Journal of Dairy Science 84 2018–2024 Torres AH, Rajala-Schultz PL, DeGraves FJ & Hoblet KH 2008 Using dairy herd
improvement records and clinical mastitis history to identify subclinical mastitis infections at dry-off. Journal of Dairy Research 75 240–247
Wallman J 2014 Erfahrungen und Schlussfolgerungen aus der Antibiotikaabgabeerfassung in der Veterinärmedizin [Experiences and conclusions from the antibiotics discharge detection in veterinary medicine]. Berlin, Germnay:
Bundesamt für Verbraucherschutz und Lebensmittelsicherheit [Federal Office of Consumer Protection and Food Safety]
Zadoks RN, Allore HG, Barkema HW, Sampimon OC, Wellenberg GJ, Gröhn YT
& Schukken YH 2001 Cow- and quarter-level risk factors for Streptococcus uberis and Staphylococcus aureus mastitis. Journal of Dairy Science 84 2649–63
3. Publikation II: New infection rate of bovine mammary quarters after application of a bismuth subnitrate-free internal teat sealant at dry-off
(Neuinfektionsrate boviner Euterviertel nach der Applikation eines Bismuthsubnitrat- freien internen Zitzenversieglers zum Trockenstellen)
Klemens Rochus Kiesner, Nicole Wente (Knorr), Jan-Hendrick Paduch, Volker Krömker
Fakultät II, Abteilung für Bioverfahrenstechnik – Mikrobiologie, Hochschule Hannover
Milk Science International 2015; 68: 10-13
Eingereicht: 17.11.2015 Akzeptiert: 17.12.2015
3.1 Zusammenfassung
Interne Zitzenversiegler werden appliziert um Neuinfektionen der Milchdrüse während der Trockenstehphase zu verhindern. Die auf dem Markt verfügbaren Präparate mit geprüfter Wirksamkeit enthalten als Hauptinhaltsstoff das Schwermetallsalz Bismuthsubnitrat. Das Ziel dieses Feldversuches war es, die Wirksamkeit eines Bismuthsubnitrat-freien internen Zitzenversieglerprototypen im Vergleich zu unbehandelten Vierteln (Kontrolle) zu testen. Dazu wurden 50 Kühe von zwei ökologisch wirtschaftenden Betrieben im „split-udder design“ behandelt. Die Studientiere waren frei von klinischen Mastitiden in der vorangegangenen Laktation und hatten somatische Zellgehalte unter 200.000 Zellen/ml in den letzten drei Milchleistungsprüfungen. Viertelanfangsgemelkproben wurden zum Trockenstellen, zwischen Tag 5 und 12 nach der Abkalbung, sowie weitere 7 Tage später genommen.
Die Neuinfektionsrate unterschied sich nicht zwischen behandelten und unbehandelten Vierteln (12,6%). Coryneforme und Koagulase-negative Staphylokokken waren die Hauptverursacher von Neuinfektionen. Die Wahrscheinlichkeit einer Neuinfektion war höher in Vierteln, die zum Trockenstellen mit Minor Pathogens infiziert waren. Kein Fall von klinischer Mastitis in den ersten 100 Laktationstagen wurde in behandelten und unbehandelten Vierteln festgestellt. Die Studie konnte keinen positiven Effekt des Bismuthsubnitrat-freien internen Zitzenversieglers bezüglich der Reduzierung der Neuinfektionsrate im Vergleich zu unbehandelten Vierteln feststellen. Zukünftige Studien mit neuentwickelten internen Zitzenversieglern sollten auf Betrieben mit höherer Prävalenz von umweltassoziierten Euterpathogenen durchgeführt werden. Weitere Untersuchungen zur Beziehung von Neuinfektion auslösendem Pathogen und dem Versiegelungseffekt scheinen angebracht.
3.2 Abstract
Internal teat sealants (ITS) are applied to prevent new intrammary infection during the dry period in dairy cattle. The common ITS products with confirmed efficacy contain the heavy metal salt bismuth subnitrate. The aim of this field study was to determine the efficacy of a novel bismuth bismuth subnitrate-free ITS prototype (BSFITS) in reducing new infections in comparison to untreated quarters (control). Therefore 50 cows from two organic German farms were treated with the BSFITS in a split-udder design. Cows included in the trial were free of clinical mastitis in the previous lactation, had a somatic cell count < 200,000 cells/mL in the last three dairy herd improvement tests. Quarter milk samples were collected at dry-off, within 5 to 12 d in milk and 7 d later. The NIR did not differ between treated and untreated quarters (12.6%). The predominant new infection causing agents were coryneforms and coagulase-negative staphylococci. The present study could not determine a positive effect of the BSFITS in reducing the NIR in comparison to untreated quarters.
Keywords: Teat sealant, bismuth subnitrate-free, new infection, dry period, minor pathogens
