Effect of Protein-Energy Relationships on the Performance and Carcass Quality of Growing Swine

Two experiments involving 348 growing-finishing pigs were conducted to study the effect of protein level, energy level, sex, and slaughter weight on growth, feed efficiency and carcass characteristics. As protein level increased above 13%, average daily gain and feed required per pound of gain decreased. Increasing the protein level decreased carcass backfat thickness, carcass yield (dressing percent) and intramuscular fat but increased yield of lean cuts (percent of chilled carcass wt.). Increasing protein level increased tissue nitrogen in experiment I but not in experiment II. Increasing energy level produced faster gains in experiment I but not in experiment II, although the higher energy levels resulted in less feed required per pound of gain in both experiments. Increased energy levels resulted in increased carcass backfat thickness and carcass yield but decreased yield of lean cuts. Energy level of ration had no significant effect on tissue nitrogen content but increased fat in the longissimus dorsi. The effect on the serratus ventralis was not statistically significant. Barrows gained faster than gilts. Little difference in rate of gain was observed between boars and gilts although boars were more efficient than gilts. Gilts had less carcass backfat and intramuscular fat, and yielded a higher percent of lean cuts than barrows. Boars had less carcass backfat and produced a higher percent of lean cuts than gilts. Gilts had a higher dressing percent than either barrows or boars. Pigs marketed at 200 lb. gained faster and had a higher dressing percent than did pigs slaughtered at 150 lb.; however, the 150 lb. pigs had less carcass backfat, a higher percent of lean cuts, a higher percent of tissue nitrogen and less intramuscular fat. There were no significant interactions between energy and protein for any of the response criteria measured.