Some Effects of Dietary Levels of Protein and Alfalfa Meal and of Antibiotic Supplementation on Growth, Feed Efficiency and Carcass Characteristics in Swine

Three levels of dehydrated alfalfa meal (experiment I) and two levels of protein with or without chlortetracycline (experiment II) were studied in a series of five trials to determine effects on feed lot performance and carcass characteristics. In experiment I alfalfa meal was increased from 4 to 16 or 28% as the individual pigs reached weights of 100, 125 or 150 lb. In experiment II, 18 and 14% protein diets with or without chlortetracycline were fed up to an average lot weight of 125 lb., then the protein levels were reduced to 15 and 11% and half the lots on each of the two antibiotic treatments were reversed. In experiment I the increase in alfalfa levels produced significant reductions in rate and efficiency of gain, dressing percent, backfat thickness, total fat percent and bacon thickness. The largest differences were caused by the 28% level of alfalfa. The weight of pig at which alfalfa was increased had little effect on the variables mentioned, although delaying the addition to 150 lb. did significantly improve the grade and increase the length of the carcasses. Significant sex effects in favor of gilts were higher carcass grades and yields of preferred cuts together with decreased bacon and backfat thickness and lower percent of total carcass fat. In experiment II the use of the high protein diet resulted in the following significant effects: increased feed efficiency, higher carcass grade, greater yield of preferred cuts, thinner back fat and less total carcass fat. Significant response to the antibiotic was limited to the first period of the experiment (up to 125 lb.) in which it increased feed consumption and decreased backfat thickness. In both experiments physical and chemical analyses of the hams reflected the results obtained from the carcass evaluation already described.