INFLUENCE OF STRAIN AND SEX ON THE RELATIONSHIP OF PROTEIN TO ENERGY IN THE RATIONS OF GROWING AND FINISHING BACON PIGS

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Abstract
Rations varying in energy (65 to 79 per cent TDN or 69 to 88 per cent apparent digestible energy) and protein (13 to 21 per cent) were studied in two experiments with 120 pigs of four strains. Rate of liveweight gain tended to be fastest in pigs fed high energy-high protein rations throughout. Males gained more rapidly than females, with strain differences being evident. Strain × sex interactions in rate of gain were present in both the growing and finishing period, with a ration × strain interaction present in the growing period. There was an indication that in the growing period pigs on high energy, particularly high energy-high protein rations ate more than pigs fed low energy rations. In the finishing period low energy rations were consumed at a higher rate than high energy rations with protein level having no influence on feed intake. In the growing period to 110 pounds, high protein rations resulted in improved feed efficiency as compared to medium protein rations, while in the finishing period to market weight high energy rations were more efficient than low energy rations. There was evidence that high protein alone or in combination with high energy rations also improved efficiency of feed utilization in the finishing period. Female pigs required less feed per pound gain than male pigs in the finishing period. High energy rations resulted in increased dressing percentage and generally inferior carcasses. There was an indication that high protein rations resulted in leaner carcasses. Carcass length was not influenced by ration. Carcasses from female pigs excelled those from male pigs in all factors measured except carcass length. Strain differences in carcass characteristics existed but no appreciable strain × ration interactions were noted.