About data recording

A field study owing, its coordination required an accommodation among farm, slaughter-house and data recording, which could not always be. accomplished. Some time-delay led to an extension of both the summer and the winter fattening period that weren't planned. The data recording at the slaughtering representing the summer fattening period lasted from the very begin of August to the end of December 2000, and the one representing the winter fat-tening period started actually at the end of February 2001 (including few slaughter groups in January and February) and lasted until the middle of June 2001. With respect to the study design (repetitive recordings from the farms in summer and winter) it has been decided not to shift records from the second period, that is, the few records in June 2001 back to the first period (summer), and vice versa (December 2000 records ahead to the winter period), taking into account a possible slight influence of season-atypical temperature within each recording period. The second reason not to shift records between the seasons was an assumed effect of "possibly improving management ability" in farms with alternative housing systems that had recently changed from CON to ALT.

Data corresponded either to the commercial data from the slaughterhouses (fat:free lean, hot carcass weight, fat score) or extra collected (planned) data (pH records, ear tag, sex and breed records, feed samples, temperature readings).

3 Monatliche Witterungsberichte der Meteo Schweiz (Monthly weather reports of Swiss Meteo) 2000 to 2001.

Material and methods

3.4.1. Slaughtering and data collection

The data collection was carried out during the regular processes around slaughtering. In the lairage, the pigs usually were shoWered, unless climatic conditions were bad and the tem-perature fell below 10 °C. The pigs designated for monitoring were tattooed differently from the rest of the daily commercial deliveries, in order to recognize the batches online and in the chiller'. The farmers and lorry drivers reported fasting and transport durations on a question-naire, which was sent to the farmers and returned by the drivers at the delivery. The pigs were mixed neither during transport nor in the lairage, according to the usual practice.

The slaughtering frequency was 240 to 250 pigs per hour (about 4 pigs per minute). After delivery, the designated pigs to be monitored at the slaughter line and in the chillers were managed as the other pigs concerning showering and resting in the lairage. On the few days when deliveries of pigs designated for monitoring were numerous, the groups had to be scheduled in the lairage to be in time for the registration of ear tag, sex and tattoo before dissection, and the pH readings at 35 minutes and two hours postmortem. This occasioned a somewhat longer lairage for a few market groups, yet not an unusually long one.

The stunning with CO2 (two pigs per cabin) was same in both slaughterhouses, whereas the scalding differed in length and method. In slaughterhouse 1, a scalding chamber was in-stalled were the bled-out pigs were showered for 8 minutes in a hanging position, while in slaughterhouse 2 the pigs were plunged into a water tank during 15 minutes, in both cases at 60 °C. After evisceration and dissection, the carcasses were chilled in a blast cooler during 80 minutes at minus 10 °C in slaughterhouse 2, whereas in slaughterhouse 1, the carcasses were not extra-fast cooled (no blast cooler installed). Fat scores, fat-free lean and carcass weight corresponded to the commercial data recording of the slaughterhouses whereas the pH was monitored extra.

3.4.2. Calibration of pH device and pH recording

The pH recording was carried out with two devices of WTW 340 portable and WTW SenTix®

SP electrodes (WTW GmbH, 82362 Weilheim, Germany).

A two-point calibration (7.00 and 4.67) was done daily before starting the measurements with a solution of Wintion® AG, 3116 Mühledorf, Switzerland) at a temperature of 35 to 40 °C for the pH-35 min and pH-2 h, and of 0 to 5 °C for the pH-24 h. The measurement of the carcass temperature combined with the pH recording was not possible online, mainly due to the slaughtering frequency. Based on preliminary measurements, default values of 39, 27 with-out and 25 °C with blast cooler, and 2 °C for pH-35/45 min, pH-2 h and pH-24 h, respectively, were set. The relatively small difference of 2 °C of the core temperature at 2 hours p.m. for the carcasses passing a blast cooler and those without is an expected value (Honikel, 2004).

The readings of initial pH had to be carried out before the carcasses went into the blast cooler in slaughterhouse 2 causing a 10 minutes earlier reading (at 35 minutes p.m.) than in slaughterhouse 1 where the readings could not be carried out only at 45 minutes postmor-tem. The time displacement was synchronised by an extrapolation (see 3.4.3.).

PH measurements were recorded at the 7th to 8th thoracic rib area (Barton Gade et al., 1995) and monitored (if possibte) in the same incision for one pH set (35 min, 2 and 24 h p.m.). The consequence was that the pH-2 h readings were systematically 0.10 to 0.15 ,units lower compared to measurements that would häve been taken in new incisions (Honikel, 2004).

This approach was carried out to keep the number of incisions in carcasses low, and for a faster recording procedure in the cooler at two hours postmortem (faster recognition of first incision) in view of minimising the inevitable time expansion (see following paragraph), and for a faster recognition at 24 h postmortem as well.

The measuring time for pH at 35 min p.m. was limited to 20 seconds per carcass, with a net 15 second gap for letting the electrode inserted in the muscle. This is the minimum required time for reliable readings (Honikel, 1998). The accuracy vvanted at pH-2 h implied an ex-tended effective measuring time of about 30 seconds per carcass due to lower temperatures.

Hence a time expansion occurred gradually increasing from the first to the last carcass of a slaughtering unit (batch of carcasses in a row), as compared to the pH at 35 minutes. This was regarded in the models (see 3,5.2.3.).

3.4.3. Plausibility of pH records and pH-45 min adjustment

A proper pH recording online depends on many factors, such as acquaintance with the slaughter process, the portable pH-device, experience of pH-measurements, etc.

Implausible pH values have been excluded from the regression models, that is when pH-35 min < pH-2 h, when pH-35 min < pH-24 h, and in the pH-24 h model when pH-24 h>

pH-2 h + 0.1. These 0.1 units regarded measuring errors at 24 hours p.m.4 of possible low pH-2 h readings that would then be excluded unjustified. The frequency of excluded records due to these implausibility conditions amounted to 2.4 and 8.6 % in slaughterhouses 1 and 2, respectively. The higher rate can partly be explained by the fact that other persons were more frequently engaged in recording the pH of carcasses in slaughterhouse 2 due to paral-lel deliveries of pigs to both slaughterhouses.

The 10-minute time displacement of the initial pH between slaughterhouses has been ad-justed in slaughterhouse 1 by extrapolating the measured pH-45 backwards to pH-35 min postmortem. The adjustment was based on the assumptions of .a linear pH-fall between 6.8 and 6.0, the early postmortem stage. The adjustment factor was calculated on a random 100

"The measuring of 2 °C cold carcasses in the chillers entailed, in the author's opinion, a certain varia-tion (reading error) which was, however, outweighed at large sample sizes.

Material and Methöds

record (98 different records) sub-sample out of 1,322 records. The latter represented slightly

>50 % of the total in slaughterhouse 1, and featured a pH-2:h p.m. of >6.0. This approach assured excluding PSE or PSE-near pigs, which would have adulterated the factor and the extrapolation. The 98 records were extrapolated individually from pH-45 min with an average of 6.517 to pH-35 min with an average of 6.559 (Table 5). The resulting difference (=slope) of 0.042 pH units was set in relation to the pH-45 min (of 98 animals) resulting in an adjustment factor of 0.0064 corresponding to 0.64 % (Honikel, 2004).

Table 5: Approach of the pH adjustment from 45 to 35 min p.m. in slaughterhouse I

Random selection of 100 records resulting in 98 different ones of a total of 1,322 records

pH-351 of 98 animals pH-451 of 98 animals

Difference between pH 35 and 45

Adjustment factor = 0.042/6.517 0.0064

Recorded pH-45 of 1,332 animals (=the total regarded for the adjustment) :6.378 New (extrapolated) pH-35 of 1,322 animals = 6.378 (6.378*0.0064) 6.419 6.559 6.517 0042

at 35 and 45 minutes p.m., respectively; explanations see text of this chapter

The extrapolated pH-35 min in slaughterhouse 1 was 6.419 (and averaged over all the re-cords, 6.418), compared to a synchronic average in slaughterhouse 2 of 6.436 at 35 min postmortem.

The installation of a blast cooler in slaughterhouse 2 could be another effect influencing the pH-fall (until pH-2 h p.m.) disparately. However, preliminary temperature recordings com-bined with pH-2 h measurements in both slaughterhouses revealed a mere 2 °C difference, i.e., on average 25 and 27 °C with and without blast cooler, respectively. A temperature dif-ference of 2 °C would have caused pH curves deviating <0.05 units and was assumed not to be relevant in the scope of this study (Honikel, 2004).

The PSE-limit of 5.80 (Honikel, 1998) or 5.90 (Barton Gade, 1995) at 45 min p.m. has been adjusted by the same factor to a new limit at 35 min p.m. of 5.84 or 5.94 according to their mentioned 45-min values.