No abstract

In order to investigate the effects of type of breed on carcass composition, an examination was made of 361 lambs from four breeds: Clun Forest and Colbred (termed ewe breeds); and Suffolk and Hampshire (termed ram breeds). The animals were in four carcass weight groups averaging 15, 17, 19 and 21 kg. Percentage subcutaneous fat was influenced more by carcass weight than by breed, whereas both carcass weight and breed had similar effects on percentage lean. At the mean carcass weight of 18 kg, Colbreds, the leanest breed, had a similar value for percentage lean (about 57 % of carcass tissue weight) to the carcasses over all breeds weighing 15 kg; and Cluns, the fattest breed, had a similar value (about 54%) to those weighing 21 kg. Since the ram breeds were intermediate in composition between the two ewe breeds there was no effect of type of breed on carcass composition. The breed differences were related to eventual mature size and to the stage of maturity at each carcass weight, as judged by body length and bone weight measurements. However, Colbreds were bigger and leaner than published estimates of their mature weight suggested. Humerus weight was a good predictor of lean or total fat weight, explaining 83 % of variation when used as a predictor along with carcass weight. Type of breed had a marked effect on internal fat deposition, the ewe breeds having heavier weights of both kidney knob and channel fat (KKCF) and caul fat (omental fat) than the ram breeds; and on the length of limb bones, the ewe breeds having longer but thinner bones than the ram breeds. The order of the relative growth of the tissues and fat depots was: subcutaneous fat > caul fat > KKCF > intermuscular fat > lean > bone. Therefore, the internal fat depots were later maturing than intermuscular fat. The percentage of prime cuts in the carcass was not affected by carcass weight. Colbreds had significantly lower values than the other breeds. Suffolks had the lowest lean to bone ratio.

1. An analysis of pre-weaning mortality in inbred Large White pigs showed that the over-all mortality in ten generations of sows was 47·3%. During the first four generations mortality fluctuated between 30 and 45%; from the 5th to the 9th it fluctuated between 50 and 68% and in the 10th rose to 88%.2. 70·2% of all deaths occurred in the first 3 days post-parturition and the average birth weight of pigs which died within 3 days was only 1003·5 g. compared with 1258·5 g. for those which survived. 83·0% of pigs weighing less than 900 g. at birth died within 3 days, whereas only 18·5% of pigs weighing more than 1400 g. died within the same period.3. There were marked seasonal variations in mortality, this being highest during the winter months. Mortality was highest in litters of under 5 and over 15, but between 5 and 15 there was no increase in mortality with litter size. There was no difference in mortality between males and females.4. Foetal growth was studied in 80 outbred sows of various breeds. Foetal weight was affected not only by age but also by litter size. The withinlitter variation in foetal weight increased with litter size but no increase in between-litter variation with litter size could be demonstrated statistically. Male foetuses were slightly heavier than females at all stages of pregnancy investigated.5. The growth of the inbred Large White foetus was also studied at an early and late stage of inbreeding, and the reduced birth weight in the latter was shown to be reflected in slower growth of the foetus from mid-pregnancy onwards.6. The anatomical composition of inbred Large White foetuses at a late stage of inbreeding has been compared with that of similar foetuses at an earlier stage and also with normal outbred Essex foetuses, at 51, 74, 97 and 108 days of pregnancy. The chemical composition of inbred Large White foetuses of a later stage of inbreeding was compared with that of outbred Essex foetuses at 51, 74, 97 and 108 days. The differences in anatomical composition between the smallest and largest foetuses within litters are comparable with those found postnatally in pigs fed on a high or low plane of nutrition, but this was not reflected in a very definite way in the chemical composition. X-ray photographs showed that ossification was more advanced in the largest foetus within a litter than in the smallest but the appearance of the ossification centres was not delayed in the latter.7. Attempts to make reciprocal ovum transfers between inbred Large White and outbred Essex sows met with little success, probably due to the low fertility of the Large Whites, the prolonged exposure of the ovum during transference and the necessity of effecting the transfer of the ova at the 2-cell stage. The latter was conditioned by the rate of passage of the ova through the tube and the fact that they enter the uterus in the 4-cell stage.

1. The contents of moisture, total nitrogen and intramuscular fat (and its iodine number), and the ultimate pH, were determined on longissimus dorsi (lumbar and thoracic regions), psoas major, rectus femoris, triceps (lat. head), superficial and deep digital flexor, sartorius and extensor carpi radialis muscles from ten pigs, of accurately known history, in each of three weight groups—pork, bacon and manufacturing (150, 200 and 250 lb. live weight, respectively).2. In addition, the myoglobin content of longissimus dorsi (lumbar), psoas major, rectus femoris, triceps (lat. head) and extensor carpi radialis was also determined. In all five muscles there was an increase in pigment content with increase of body weight, but there was some suggestion that the myoglobin content of psoas major and triceps showed a proportionally greater increment between pork and bacon weights and rectus femoris and extensor carpi radialis between bacon and manufacturing weights.3. In pigs of all three weight groups there were highly significant differences in fat-free moisture content between muscles and between animals. The mean, fat-free moisture content of longissimus dorsi (lumbar) (76·33%) is significantly less than that of longissimus dorsi (thoracic) (76·94%) and the mean value in the latter is significantly less than that in all the muscles except psoas major (77·28%). The mean fat-free moisture content of deep digital flexor (80·00%) is significantly higher than that in all the other muscles studied. There is evidence for a direct, but not linear, relationship between the contents of fat-free moisture and connective tissue (as calculated from hydroxyproline concentration).4. Differences in ultimate pH between animals and between muscles were highly significant; but not those between the three weight groups, although there was a tendency for higher values in the muscles from bacon and manufacturing groups.5. Both for the data overall, and within a given muscle, there was a direct proportionality between ultimate pH and fat-free moisture content. Except in the case of deep digital flexor correlation coefficients between these two parameters were significant. These correlations varied in significance for different muscles between the three weight groups.6. Overall, the mean total nitrogen content (fat-free) of longissimus dorsi (lumbar) (3·77%) was significantly greater than that of longissimus dorsi (thoracic) (3·69%) and the latter greater than that of psoas major (3·58%). Such differences were also apparent within each weight group. The values were significantly greater than those for the six other muscles studied. The overall mean fat-free nitrogen content of deep digital flexor (3·17%) was very significantly less than that for all the other muscles. For the muscles of pork, bacon and manufacturing weights, overall nitrogen contents (fat-free) were 3·38, 3·44 and 3·55%, respectively. There was a significant inverse correlation between nitrogen (fat-free) and moisture (fat-free) (r = –0·88).7. The ranking of muscles with respect to their contents of intramuscular fat was significantly different between weight groups. In contrast to the bovine, there was no significant difference overall between the intramuscular fat contents of longissimus dorsi in lumbar and thoracic regions; and these were both significantly higher than levels in psoas major, although the converse is true in the bovine.8. Variation in the intramuscular fat content of the lumbar region of longissimus dorsi was strongly reflected by those in longissimus dorsi (thoracic), psoas major, rectus femoris, triceps and superficial digital flexor; but little with those in extensor carpi radialis and deep digital flexor; and not at all with that in sartorius.9. There was no significant difference overall in the iodine number of intramuscular fat between weight groups. Iodine numbers in both thoracic and lumbar regions of longissimus dorsi were significantly lower than those in all the other muscles studied. The overall correlations between intramuscular fat and its iodine numbers were r = –0·70, – 0·71 and – 0·66 in pigs of pork, bacon and manufacturing weights: each of these was significant.10. In discussing the results, it is suggested that those circumstances causing a high ultimate pH in muscle (e.g. fatigue) may concomitantly effect redistribution of body water and hence explain the observed proportionality between water content and ultimate pH. Significant differences in moisture content between muscles may be related to their relative proportion of connective tissue or to its nature. On the basis of much of the chemical data obtained, the muscles studied appear to fall into three groups—longissimus dorsi (lumbar and thoracic), deep digital flexor, and the rest, although such a conclusion does not accord with that suggested by anatomical dissection. Aspects of the relative maturity of the muscles are considered.

Five inbred Large Whites from the same strain as used by McMeekan (1940) were reared on a High Plane of nutrition to approximately 330 lb. live weight at which one was killed as a control. The rest were put on to a submaintenance diet of straw and water and killed successively at roughly equal intervals in live weight between 330 and 200 lb. The weights of blood, organs and offals were determined and the carcasses were jointed and completely dissected into their constituent tissues. The total weights of each and the weights within the various joints were recorded.(1) Organs. The early-maturing organs, brain, eyes, etc., continued to grow. Other organs like the heart, liver, lungs, etc., suffered a greater or less degree of atrophy which was probably determined by a suspension of their functions.(2) Carcass composition. The tissues of the carcass were affected in reverse order to their development, i.e. fat most, muscle less and bone least. Bone continued to grow in the earlier stages of submaintenance.