Antibiotics in Dairy Cattle Nutrition. III. Effects of Different Levels of Aureomycin Intake upon the Growth and Well-Being of Dairy Calves, and the Association of Differences with Changes in Environment

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Abstract
Thirty Holstein and Jersey calves 4 days old were divided at random by breed and sex into 3 groups. Two groups of calves received either 15 or 45 mg. of Aureomycin (Lederle''s Aurofac) daily per 100 lb. wt.from 1 to 25 wks. of age. A 3d group served as controls. The expt. was conducted in a barn that had not housed calves previously and results were compared with those of a previous expt. in which the calves were fed a 15 mg. level of Aureomycin and raised in an old barn that had proved unfavorable for successful calf raising. Sickness was not as great a problem in the new quarters as in the old. In the new quarters both levels of Aureomycin feeding reduced the incidence of infection. Calves fed no Aureomycin in the new quarters grew as rapidly as calves fed Aureomycin in the old quarters. However, Aureomycinfed calves in the new quarters grew at a significantly faster rate than their controls. In the new quarters the 45-mg. level was more effective than the 15-mg. level in controlling the types of infections encountered. The growth rate of both breeds considered together was increased significantly by the 15 mg. level of Aureomycin feeding. Another statistically significant increase resulted when the level of Aureomycin was increased from 15 to 45 mg., but the rate did not increase in pro-portion to the increased Aureomycin intake. Calves receiving 15 mg. of Aureomycin consumed 19% more hay than the controls, and those receiving 45 mg. consumed 38% more than the controls. These differences were not statistically significant. The differences in grain intake followed the same trend as the differences in hay intake but were not as great and also were not significantly different. The calves receiving 45 and 15 mg. of Aureomycin used less total digestible nutrients and less digestible protein per lb. of gain than the control calves. These differences were not statistically significant.