Effects of a Commercial Direct-Fed Microbial on Weight Change,Milk Yield,and Milk Composition in Lactating Beef Cows: A Case Study

Feeding a commercial direct-fed microbial product (DFM) to lactating Angus cows (n = 22) was investigated from d 53 to 123 of lactation. Cows were fed ad libitum hay (alfalfa, wheat, or rye, depending upon period) with supplemental grain, whereas the DFM was fed at a rate of 28.4 g/d per cow to 12 cows, and 10 cows received no DFM (Control). Beginning at an average of d 67 of lactation, cows were machine milked every 14 d to measure milk yield, percent protein, percent fat, and somatic cell count (SCC). Calves were separated from cows 18 h before milk collection, and all calves and cows were weighed on each collection day before milking. Data were analyzed as a repeated measures design where treatment, cow nested within treatment, time, and time x treatment interaction were the independent variables. Milk yield, protein percent, and SCC did not differ between cows receiving DFM and Control cows, but milk from cows receiving DFM had higher (P<0.05) percentage of fat (3.84 vs 3.33%). Cows receiving DFM lost less weight (P<0.05) than Control cows (?0.06 kg/d vs ?0.31 kg/d) over the entire trial, but this was quite variable by period. Time and treatment interacted; those receiving DFM gained weight in three of five periods, whereas Control cows gained weight in two periods. There were no differences in calf weight gain between treatments, nor were there differences in cow weight or calf weight at weaning between DFM and Control groups.