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Influence of Level of Dietary Protein on Live Weight Gains and Carcass Characteristics of Swine¹

University of Minnesota, St. Paul

Abstract

Two hundred twenty-six weanling pigs were fed in four experiments to determine the influence of protein content of otherwise well-balanced rations on various measures of carcass merit and on rate of gain and efficiency of feed utilization.

Protein levels compared in three experiments were 18 and 14% initially, each level being reduced three percentage units when the pigs weighed 125 lb. In the fourth experiment initial levels of 16 and 14%, reduced to 11% at 125 lb. were compared with a 12% level fed throughout the experimental period. Carcass measurements included average back fat thickness, length, percent lean and fat and dressing percent. In all but the first experiment the percent of four lean cuts of chilled carcass was measured and the loin eye area was measured in the last two experiments.

One hundred ninety-nine carcasses were evaluated. Differences due to protein level were not significant statistically. There were fairly consistent small differences in several measurements in favor of the higher protein levels. There was a highly significant effect of breed (P<.01) on all measures of carcass leanness and fat in each of two experiments in which purebred animals were fed.

Initial protein levels of 14, 16 or 18% did not have a significant effect on daily gains. A highly significant decrease (P<.01) in daily gain was observed when weanling pigs were fed a 12% protein diet up to a weight of 125 lb., as compared with those fed 14 or 16% protein. In two experiments there were highly significant differences in daily gain between breeds.

The data support the thesis that the genotype of the animal fed is the important factor in carcass leanness and that initial protein levels for weanling pigs within the range of 14 to 18% have only minor effects on carcass quality.

¹ Paper No. 4454 Scientific Journal Series of the Minnesota Agricultural Experiment Station.

² Acknowledgement is due Swift and Co., South St. Paul, for cooperation extended during collection of carcass data; Glen Swartz and associates who fed and cared for the pigs; Whitney Lindwall and Edward Haeg who assisted in collection of carcass data; and Manuel Soldevila for the statistical analyses.