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Different Protein Levels with and without Antibiotics for Growing-Finishing Swine: Effect on Carcass Leanness^{1, 2, 3}

Iowa Agricultural Experiment Station

Abstract

Measurements on length of carcass, specific gravity, percent lean cuts, cross-section area of the loin muscle, live probe, depth of backfat, and weight of leaf fat from 102 swine carcasses are reported in this study. The test rations were fed to the pigs throughout the feeding period without alteration of composition.

While there were some discrepancies in the uniformity of response to the imposed experimental treatments in the two experiments in this study, the results are in close agreement. They give no indication that the inclusion of the antibiotics, aureomycin or terramycin, at 5 mg. per lb. of ration in a corn-soybean oil meal ration fed to pigs from weaning to 200 lb. liveweight had an important effect on hog carcass quality.

Feeding pigs protein levels over the range from 10 to 20 percent of the ration resulted in carcasses with a significantly greater proportion of lean as the level of protein increased. This increment in proportion of lean per interval of protein (two units percent) increase is of such small magnitude, however, as to be of minor consideration when a choice must be made between two adjacent protein levels.

¹ Journal paper No. J-2557 of the Iowa Agricultural Experiment Station, Ames, Iowa. Animal Husbandry Department. Project 930.

² This work was partially supported by grants from Lederle Laboratories Division, Pearl River, New York, and Chas. Pfizer and Co., Brooklyn, New York. The vitamins and antibiotics were also supplied by them.

³ The terms aureomycin and terramycin are used to refer to chlortetracycline and oxytetracycline, respectively, throughout this manuscript.

⁴ Present address, Animal Husbandry Department, Oklahoma A. & M. College, Stillwater, Oklahoma.

⁵ Present address, Department of Animal Science, University of Illinois, Urbana, Illinois.

⁶ Present address, Lederle Laboratories Division, New York, New York.

⁷ Acknowledgment is made to Prof. Paul Homeyer for his assistance in the statistical analyses of the data and to Mr. Julius Jensen and his associates of the Meat Laboratory for their cooperation.