Hampshire and Large White crosses were compared with purebred Large White pigs for litter production and post-weaning performance. Crossbreeding did not influence either litter size or total litter weight at birth but crossbred litters had 14 % more pigs at weaning than purebred litters. Total litter weight at weaning was 13 % greater in crossbred litters. In two post-weaning trials (23 to 90 kg live weight), where feeding was either ad libitum or restricted according to live weight, Hampshire crosses had advantages over Large Whites in rate and efficiency of gain and killing-out percentage. The crossbreds had shorter carcasses but a greater eye-muscle area due primarily to a greater depth of lean in the muscle. All fat depth measurements indicated that the crossbreds were not significantly leaner than the purebreds and this was confirmed in the restricted trial when the carcasses were subjected to physical and chemical dissection. Hampshire carcasses did have a lower bone content than those of the purebreds, but crossbreeding did not influence joint proportions or lean distribution in the carcass.

A Quality characteristic of the bacon side is the fat to lean ratio of the rashers obtained from it. Although this measurement has received attention in carcass evaluation (Pearson, Bratzler, Hoefer, Price, Magee and Deans, 1956; Lucas and Mitchell, 1962; Jonsson, 1963), unlike many others its accuracy as a predictor of lean content of the carcass has not been established. On this basis it was considered worth while to undertake an analysis of the method.

SUMMARYA trial is described in which normal rations containing oleandomycin at 12½ and 25 g. per ton of meal and without the additive were given to females and castrates which had previously received creep feed with and without oxytetracycline.A total of 48 pigs were individually fed on the rations from 50 to 200 lb. live-weight, a restricted scale of intake based on live-weight being adopted.Between 50 and 100 lb. live-weight rate and efficiency of gain were significantly better in pigs which had not received antibiotic in the creep feed. No other treatment had any significant effect on performance.Oleandomycin did not influence carcass measurements or dressing percentage. Minimum depth of fat at the mid-back was significantly greater in pigs which had received oxytetracycline in the creep feed while castrates had a significantly greater depth of fat at the shoulder and mid-back compared with females.Pigs receiving the lower level of oleandomycin had significantly lighter kidneys than the control animals. Other visceral weights were not significantly influenced by the antibiotic, but females had significantly heavier kidneys, spleen and liver weights than castrates.

No abstract

1. Normal rations containing oleandomycin (2·5 g./ton), oxytetracycline (10 g./ton) and oleandomycin (2·5 g./ton)plus oxytetracycline (10 g./ton) were given to females and castrates which had previously received creep feed with or without oxytetracycline.2. Forty-eight pigs were individually fed on the rations from 50 to 200 lb. live-weight, a restricted scale of intake based on live-weight being adopted.3. Pigs receiving the mixed supplement and those given oxytetracycline alone grew significantly faster and utilised their feed more efficiently than those given oleandomycin alone. Differences between the mixed supplement group and those receiving oxytetracycline were not significant.4. Treatment with antibiotic, either in the creep feed or after weaning, had no effect on carcass measurements. Females had less depth of fat at the shoulder, mid-back and loin compared with castrates and the carcasses were significantly longer.5. Visceral weights were not influenced by antibiotic treatment but pigs supplemented with oleandomycin had a shorter gut than those receiving a combination of antibiotics. There was a significant reduction in gut weight n i pigs which had received unsupplemented creep feed but no consistent effect on the thickness of the intestine wall or gut diameter. Females had significantly heavier kidneys and spleens than castrates.