Working hypotheses
The aim of the present thesis was the evaluation of tail-biting behaviour in pigs in order to gain further information on the causes and the underlying mechanism of this abnormal behaviour. Therefore, two different experimental set-ups concerning environmental enrichment and weaning management were carried out under practical conditions. In the first study, the focus was on the effect of manipulable material provided to piglets. In contrast to former studies in this research field, the focus was on the farrowing and rearing phase instead of the fattening period. The assumption was made that a daily provision of raw material from the second week of life until the end of rearing could help to prevent tail-biting behaviour in pigs. In the second study, the concern was weaning management since reliable information on optimal weaning management and its effects is still insufficient. The hypothesis was proposed that the rearing of siblings and, thus, a renunciation of mixing after weaning can prevent tail-biting during rearing. The data in both studies were collected with a scoring scheme taking into consideration both tail lesions and tail losses. Additionally, video observations in the environmental enrichment study delivered data on the activity behaviour of the piglets at group level and occupation with the material provided. The focus of the video analysis in the weaning management study was on manipulative behavioural patterns and the piglets’
behaviour prior to a tail-biting outbreak, thereby providing further information on character differences at individual level.
Raw material
Nowadays, animal welfare receives more public attention and is widely discussed on farms.
The five freedoms of animal welfare declared by the UK Farm Animal Welfare Council (FAWC, 1979) are the freedom from hunger and thirst, from discomfort, from pain, injury and disease, from fear and distress and the freedom to express normal behaviour. Especially the last point is important regarding the development of behavioural disorders, because barren environments of intensive housing systems do often not meet the natural demands of the animals. If the aversive situation for the piglets consists of the absence of a stimulus to release a specific behaviour (e.g. rooting), exploratory behaviour is the adaptive coping response
(Wechsler, 1995). Unsatisfied foraging behaviour could lead to more manipulation of the tail of a pen mate, resulting in tail wounds as described by Taylor et al. (2010). The results of Douglas et al. (2012) show that pigs have more optimistic judgement biases in enriched environments indicative of a more positive affective state. Also, pigs that have spent time in an enriched environment react more negatively to being subsequently housed in a barren environment. Several aspects of a realisation of environmental enrichment in intensive husbandry are discussed below.
A problem in the environmental enrichment study was that in pens housing 24 piglets (two litters combined) one piglet bowl resulted in a piglet to occupation ratio of 2.4:1, which implied that not every piglet reached the provided material at the same time. The limited size of a point source may restrict access to enrichment causing competition, aggression or restlessness in groups of animals (Van de Weerd et al., 2006). Pigs’ feeding behaviour follows a synchronic pattern, a reason why a ratio which exceeds 1:1 is unfavourable. Hansen et al. (1982) showed a clear connection between the frequencies of aggression, tail- and ear-biting comparing piglets with access to one feeder in comparison to several feeders.
Nevertheless, there were no significant differences regarding tail-biting in the raw material groups between the pens housing 24 piglets and the pens housing 12 piglets.
A point of discussion should be the fibre length, which was relatively short (about 50 mm) in both materials. Day et al. (2008) concluded that the number of tail-biting incidents was higher in groups with short-chopped straw (mostly 1 to 40 mm) in comparison to partially chopped (mostly 40 to 70 mm) or long fibre straw (mostly over 70 mm). Nevertheless, based on experiences from other on-farm studies in which long fibre straw (over 70 mm) led to massive problems with the slurry system the decision was made to find a trade-off between suitable materials for piglets and intensive housing systems (Van de Weerd and Day, 2009).
Furthermore, the offering scheme per day should be discussed. In the environmental enrichment study an effort was made to provide the material twice a day, whereas the offering scheme in the weaning management study was only once per day. In this study, only small pens were used and the offering scheme was a relief for the stable staff in order to save time.
Nevertheless, the material did often not last throughout the day and empty piglet bowls can also be seen as a frustrating factor in the pen. Munsterhjelm et al. (2009) concluded that moderate bedding of farrowing pens reduces agonistic behaviour later in life, although
removal of it increases redirected behaviour, including tail-biting. This might have been problematic in the environmental enrichment study; the piglets from the raw material groups did not receive alfalfa hay and corn silage during fattening. The results show that piglets which received raw material from the second week of life until the end of rearing lost their tails to a larger extent during fattening (20 %) than piglets out of the control groups (5 %).
Thus, as stated by Munsterhjelm (2009), the withdrawal of material provided in former stages of life can be interpreted as a frustration factor which could have provoked tail-biting in the subsequent fattening period. Additionally, Day et al. (2002) proved that moving pigs from previously straw-bedded accommodation to not straw-bedded accommodation increases the occurrence of adverse pen-mate-directed behaviour.
Moreover, it is important to mention the renewing aspect of raw material provision as described by Moinard et al. (2003) and Hunter et al. (2001). The material remained of interest to the animals as long as it was renewed regularly and did not smell like the pen surroundings or the piglets themselves. This cannot be guaranteed by occupation material which is permanent available in the pen such as chains, plastic balls or wooden sticks. Wood-Gush and Vestergard (1991) proved piglets’ preference for novelty when offered a familiar object in comparison to a novel object. This emphasises piglets’ curiosity and the value of frequent renewal of manipulable material. Especially dried corn silage seemed to be suitable to stimulate the exploratory behaviour of the piglets for a certain length of time. This finding contributes to Studnitz et al. (2007), who concluded that if the material is complex and if it is changeable as well as destructible, the novelty value will be maintained. Furthermore, if the materials contain edible parts, the foraging behaviour as well as the curiosity of the pigs will be stimulated.
Weaning management
The starting point of tail-biting was detected in both studies in the second week after weaning, which implicates a relation to the weaning process. Martin (1984) defined weaning as the period when the drop in parental investment per unit time is the largest. Under “natural conditions” weaning is a gradual process and in piglets is not completed until 10–12 weeks of age (Lallès et al., 2007). The piglets are taught how to feed and to root and learn to establish their hierarchy in the group (Oostindjer et al., 2014). In a current study the effect of a
prolonged suckling period in a group farrowing system is being tested in order to evaluate whether the piglets’ behaviour is positively influenced by the longer presence of the sow.
What needs to be evaluated here is whether abnormal behaviour re-surfaces in connection with the weaning process as in previous studies or at another point of time. Nevertheless, the abrupt change in housing environment and separation from the sow as well as the confrontation with unfamiliar pen mates requires a high coping ability of the piglets. Stress physiology is often called physiology of adaption. Any challenge facing an animal leads to a modification of the functioning of that animal, and this change prepares the animal to better cope with further challenges (Veissier and Boissy, 2007). Tail-biting as a stress-induced behavioural disorder (Sinisalo et al., 2012) is caused by several risk factors which can accumulate and influence the overall risk of an individual piglet to show abnormal behaviour (EUWelNet, 2013). Wiepkema and Van Adrichem (1987) described that conflict behaviour arises during acute stress, whereas chronic stress brings about disturbed behaviour such as stereotypes. An animal is said to be in a state of stress if it is required to make abnormal or extreme adjustments concerning its physiology or behaviour in order to cope with the adverse aspects of its environment and management (Fraser et al., 1975). Coping is defined as a behavioural response that aims at reducing the effect of aversive stimuli (Wechsler, 1995).
Welfare is defined as the state of physical and mental health resulting from the process of behavioural and physiological adaptation when coping successfully with environmental challenges (Puppe et al., 2012). In intensive housing systems, however, the animals often fail to counteract aversive situations by using these evolved coping strategies, and it is argued that abnormal behaviour can originate from unsuccessful coping behaviour (Wechsler, 1995).
Both failure to cope with the environment and difficulty in coping are indicators of poor welfare (Broom, 1991).
Is the weaning process one of the triggering factors which can provoke subsequent tail-biting behaviour or does the weaning process occupy the piglets with the exploration of new environmental surroundings, as well as the meeting of new pen mates? Expressing it in more abstract manner: Are the piglets’ overwhelmed by today’s management practices (such as regrouping, rehousing…) and do we overtax their adaptive abilities or, have the piglets with their individual coping strategies which enable them to react to environmental changes developed such a flexibility that a “standstill”, which is provoked e.g. by barren rearing pens,
results in frustration and boredom? Korte et al. (2007) assumed that not constancy or freedoms, but capacity to change is crucial to good physical and mental health and good animal welfare.
Underlying mechanisms and coping strategies
Tail-biting occurred in both studies regardless of the treatment groups. The variable results suggest a connection between the behavioural disorder and the individual character of the piglets, which was detected by video analysis in the weaning management study. Dantzer and Mormède (1983) stated that behavioural responses follow two opposite modes, a passive mode (e.g. freezing) vs. an active mode (e.g. fight/ flight), which (both) depend on the individual’s genetic background and prior experience. Hessing et al. (1993) found proof of the existence of behavioural strategies to cope with conflict situations in piglets. Koolhaas et al.
(1999) concluded that there are distinct phenotypes (proactive and reactive coping styles) which are more or less stable over time in their response to stressors and, thus, may adapt differentially to environmental conditions. Transferring this assumption to the results of the video analysis, the coping style of receivers of tail-biting would be classified as passive since they stop to perform overt behaviour when exposed to an aversive situation and wait for a change (Wechsler, 1995). Performers on the other hand could be seen as active coping types, which react to aversive situations with abnormal behaviour. Korte et al. (2009) assumed that artificial genetic selection (fast growth, leaner meat, larger muscle volume) results in the production of farm animals that prefer the aggressive hawkish behavioural strategy and, thus, have a higher risk of developing violence and stereotypes. Nevertheless, focusing on welfare aspects in breeding, it needs to be kept in mind that breeding against behavioural measures of welfare could inadvertently result in resilient animals that do not show behavioural signs of low welfare yet may still suffer (D'Eath et al., 2010).
Prediction of tail-biting events on commercial farms
One part of animal behaviour important for the prediction of tail-biting outbreaks is tail posture. In the course of both studies, no data on this trait were collected, but direct observations made during the weekly scoring gave an indication that tail posture is linked with tail-biting outbreaks. In case of an incidence in a pen, the piglets waved their tails more
frequently and piglets which had already received bites, tucked their tails under to prevent further manipulation. This contributes to the study of Zonderland et al. (2009), who concluded that a piglet’s tail posture is strongly related to tail damage at the same moment and can predict tail damage two to three days later. Thus, long tails in piglets can be used as an “early alert” system, since any management problem which causes tail-biting, such as dysfunction in feed- or water accessibility as well as climate deficiency, could then be detected.
Another observation that could be made was the piglets’ behaviour when entering the pen in order to score the tails. In pens with tail-biting outbreaks, the piglets showed different behaviour towards the observer. This trait was subjectively evaluated and not consequently documented during the studies. In the case of a tail-biting outbreak, piglets were more obtrusive, searched contact with the observer more quickly, and manipulated the observer more frequently. The most possible objective way of assessing this is probably the human approach test. In this test, a human enters a pen and documents the latency until the piglets perform their first physical contact with the observer (Brown et al., 2009).
Furthermore, there is evidence that changes in feeding patterns are connected with tail-biting outbreaks. Wallenbeck and Keeling (2013) showed that low frequencies of daily feeder visits observed at group level can predict future tail-biting in the pen as early as nine weeks before the first tail injuries. Therefore, feed consumption could be a parameter which should be considered in further studies.
Recommendations for further research
In both studies, the animal to feeding place ratio was 2:1, which inhibited stress-free feed intake for the piglets. An insufficient animal to feeding place ratio increases the risk for tail-biting (Hansen et al., 1982; Moinard et al., 2003). Evaluations should be carried out as to whether a ratio of 1:1 has positive effects on the development of the behavioural disorder.
Another aspect could be feed composition (especially crude fibre content) and the dosage form of feed (liquid vs. dry), since information available in literature is inconsistent.
A further focus should be put on genetics since there is an indication that a higher lean meat content and decreasing back fat thickness is connected with increasing frequencies of tail-biting (Moinard et al., 2003). In the last few decades, consumers have shown a growing interest in higher lean meat content due to fitness aspects, which have resulted in a more
targeted selection. It needs to be clarified whether the breeding in turn affected the piglets’
behaviour as mentioned above.
Individuals which showed the obsessive form of tail-biting, as described by Taylor et al.
(2010), could be detected by direct and video observation in both studies. If these animals tail-biting as a stereotype developed due to chronic stress probably caused by health problems or malnutrition cannot be sufficiently clarified. A point of interest in identified biters would be the analysis of blood and brain serotonin measures, which are related to dietary tryptophan supply and play an important role in stress metabolism (Koopmans et al., 2006). The results of Ursinus et al. (2013) suggest a role of serotonin in biological traits underlying the behavioural responses of pigs during a challenging situation.
Moreover, diseases such as infections caused by E.coli and Streptococcus suis occurred in both studies and probably led to increasing tail-biting behaviour in affected pens and units, subsequently. There are indications that a proper health status is of crucial importance in the prevention of tail-biting (Moinard et al., 2003; Walker and Bilkei, 2006); pigs which are infected may be more reluctant to defend themselves against being bitten (Kritas and Morrison, 2004). The serum acute phase proteins haptoglobin, respectively C-reactive protein, as indicators of inflammatory reactions can provide an important marker for swine health status in further studies (Chen et al., 2003).
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