A survey of pH1 and ultimate pH values of British progeny‐test pigs

Abstract

Summary. 1. A total of 2878 progeny‐test pigs from five stations, and of 1532 commercial pigs, were surveyed for the pH1 values, at 45 min after death, and the ultimate pH values, at 24 hr after death, of their LD muscles at the last rib. Values are also available for the heads of the adductor and semimembranosus muscles, where they are exposed in the gammons on splitting the carcase.2. Factors which affect the pH1 values are the method of stunning, the breed of pig and the waiting time between station and factory, before slaughter.(a) CO2 stunning lowers the mean pH1 values and increases the % of these values lying below pH 6.0 about three‐fold, as compared with electrical stunning. The effect is easily detectable. In extreme cases, a distinctly bimodal distribution of the pH1 values appears with CO2‐stunned pigs.(b) Of the progeny‐tested breeds, Large White shows the lowest % of low pH1 values and Welsh and Landrace the highest, but the differences (about two‐fold) are not as marked as those brought about by changing from electrical to CO2‐stunning of any particular breed. Commercial pigs of mixed breed, for instance, show a lower % of low pH1 values even than Large White, but this % can be raised beyond that for electrically stunned Large White, if the commercial pigs are stunned with CO2.(c) Waiting time between leaving the station and slaughter has a marked effect on the shape and position of the frequency polygons for pH1. As the time is increased, so the frequency polygons become broader, the mean pH1 shifts to lower pH values and the % of values below pH 6.0 increases. At the shortest waiting times, the frequency polygons and the other two parameters for progeny‐tested pigs are almost indentical with those for commercial pigs, and may even be an improvement on them, in the sense that the tendency to watery pork is further decreased. This effect of waiting time is independent of ambient temperature, which itself affects the distribution of pH1 values but only to a minor degree. There is, similarly, a tendency for the % of low pH, values to be affected by season, being lower in spring and early summer than in autumn and winter, contrary to expectation.3. Factors which do not significantly affect the distribution of the pH, values, or their mean, are the sex of the pig, and the deep muscle temperature at 45 min after slaughter. In fact, the pH, values are completely randomly distributed with respect to deep muscle temperature which in its turn appears to be quite unrelated to the ambient temperature in the holding pens or the factory.4. There are some differences between the pH, values of gammon and LD muscles, the former tending to be slightly higher on average, but randomly distributed, so that a pH, value of below 6‐0 in the LD muscle may be accompanied, on the same carcase, by one of 6.30 or higher in the gammon or vice‐versa. For the purposes of an overall survey of the likely occurrence of watery pork, the differences between the two muscles are negligible.5. The ultimate pH values of the progeny‐tested pigs are raised as the waiting time before slaughter increases, due no doubt to increased utilization of glycogen reserves during the tension and excitement of waiting. Ambient temperature, on the other hand, has no significant effect on the ultimate pH, even at the longest waiting time of 1 ½ hr, although the pigs may have been exposed during his time to temperatures below 4.5°C. Hence, the wastage of glycogen by shivering, observed by earlier workers, does not seem to occur here.The grand mean of all the ultimate pH values was 5.68, which is higher than that of 5.50 usually observed in large samples of Danish Landrace.