Effect of Protein Level and Quality in Swine Rations upon Growth and Carcass Development

Rations containing 16% and 12% total protein- were found to support good growth of swine from weaning to 200 lb., when these rations contained small amounts of a high quality protein source such as brewers' yeast and dried skimmilk. Dressing percentage was lowest in the slowest gaining group, which received the 16% poor quality protein ration. The weights of liver, leaf fat and kidneys were not affected by treatment. However, there was a tendency toward heavier liver and kidneys and less leaf fat at early growth stages in pigs fed the superior ration. Gilt carcasses contained more muscle and less fat than carcasses from barrows. Carcasses from pigs fed a 16% good quality protein ration were more muscular as shown by a greater cross sectional area of the longissimus dorsi muscle (except at 205 lb.), increased carcass specific gravity, higher levels of carcass protein and decreased fat back thickness. The intramuscular fat of the longissimus dorsi was lowest and the percentage moisture in the carcass was highest in the 16% good quality protein group. It appeared that carcass muscle development was more severely hindered in early growth than in later growth by low protein level and/or quality.