Document Type

Dissertation - Open Access

Award Date


Degree Name

Doctor of Philosophy (PhD)


Animal Science

First Advisor

Richard C. Wahlstrom


Two hundred sixteen crossbred barrows and 96 crossbred gilts were used in a series of three experiments to determine the effect of dietary protein level during three different growth periods on growth am quantitative and qualitative carcass traits of the growing-finishing pig. Pigs were fed from approximately 20 to 113 kilograms. Corn-soybean meal diets fortified with recommended levels of vitamins, minerals and an antibiotic were fed. Pigs fed 20, 18 or 16% protein diets from weights of 20 to 45 kg gained both significantly faster and more efficiently than pigs fed diets of 12% protein. Feeding a low (12%) protein diet in period one followed by a high (16 or 18%) diet in period two resulted in compensatory growth during this second period. Pigs fed 16 or 18% protein diets in period two gained considerably faster and more efficiently when their previous diet contained 12% protein than when they were fed diets of 18 or 20%, protein during the initial period. Pigs fed 18% protein diets gained significantly faster and more efficiently than those fed 10% protein regimens from 45 to 77 kilograms. From 77 to 113 kg there were no significant differences in rate of gain or feed efficiency when pigs were fed diets of 12, 14, 16 or 20% protein. Diets of 10% protein were not adequate if preceded by diets also low in protein content; however, if preceded by diets adequate in protein, gains were not reduced when 10% protein diets were fed during this period. However, pigs fed a 10% protein level required significantly more feed. Significant treatment differences existed in rate of gain and feed per gain for the entire growth period, 20 to 113 kg, when pigs were fed a protein regimen of 12-10-10, 12-10-18, 12-18-18, 18-10-10, 18-10-18, 18-18-10 or 18-18-18%. Fastest gains were obtained by pigs fed an 18% protein level continuously, while most efficient gains were by pigs fed a 12-18-10% protein sequence. Pigs fed a 12-10-10% protein sequence gained the slowest and least efficiently. Daily gains were similar for pigs fed protein sequences of 18-16-16, 18-16-14, 18-16-12, 18-16-10, 18-12-16, 18-12-14, 18-12-12 and 18-12-10%. However, feed efficiency was lower for pigs fed 18-16-10 and 18-12-10% protein sequences. Area of the l. dorsi muscle, ham and loin and lean cuts percent were decreased when pigs were fed low protein diets during all three growth periods or during the last two growth periods. Carcass backfat was increased when low protein diets were fed. No significant treatment differences occurred in either carcass length or dressing percent. Fat content of the l. dorsi muscle increased 74, 193 and 106% when low protein diets were fed in experiments 1, 2 and 3, respectively. Protein and moisture content of the l. dorsi muscle increased when high protein regimens were fed. However, these changes were not as great as changes in fat content. Treatment differences in tenderness, flavor, shear test, color and firmness score and cooking loss of the l. dorsi muscle were not significant. Marbling score was increased significantly when pigs were fed low protein diets. Juiciness score was more desirable for the low protein groups, but the differences were not consistent. Results suggest that low dietary protein levels reduce growth performance if fed early in the growth period of the pig. In addition, low dietary protein regimens reduced carcass meatiness and increased intramuscular fat.

Library of Congress Subject Headings

Swine -- Feeding and feeds
Proteins in animal nutrition



Number of Pages



South Dakota State University