Addition of Soybeans or Methionine Analog to High-Concentrate Rations for Dairy Cows

Twelve lactating cows were used in two trials with a 3×3 Latin square design. In each trial, control rations were compared with the addition of methionine analog or ground soybeans. In Trial l the concentrate-to-roughage ratio was 3:1 whereas in Trial 2 it was 2:1. In Trial 1 the addition of soybeans resulted in a significant decrease in milk production (18.3 versus 15.4kg/day) and milk fat percentage (2.5 versus 1.8%). Weight percentages of rumen acetate and butyrate were significantly decreased while those of propionate increased significantly. There was a marked increase in the unsaturation of circulating lipids as well as milk fat. Some scouring and feed refusals occurred during soybean feeding. Feeding methionine decreased butyric acid concentration in the rumen; no other tested component was altered. In Trial 2, feeding soybeans slightly increased milk fat percentage compared to controls (3.8 versus 3.6%). Soybeans did not alter milk yield or rumen volatile fatty acid patterns. No deleterious side effects were observed. Methionine analog had no significant effect on milk fat test, yield, circulating lipids, or rumen volatile fatty acid percentages.