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Effect of Particle Size of Soybean Meal on Protein Utilization in Steers and Lactating Cows¹

Department of Animal Science, Oklahoma State University, Stillwater 74074

ABSTRACT

The effect of particle size of soybean meal on protein utilization was examined in two trials. In trial 1, four steers with ruminal and abomasal fistulas were in a 3 x 3 Latin square design with column added to estimate the effect of particle size on degradation of protein in the rumen. Rations of prairie hay and ground corn were supplemented with either finely ground or of a coarser particle size. Abomasal nonammonia nitrogen passages were 170, 236, and 217 g/day for steers fed rations containing urea and fine and coarse soybean meal. Calculated by difference, bypass of nitrogen was 61.4 and 44.7% for fine and coarse soybean meal. Neither rumen ammonia concentration nor digestibility of ration components was changed by particle size.

In trial 2, 24 Holstein cows were fed fine and coarse soybean meal at 14.5 and 32.8% of the concentrate mixture. Milk yield, rumen ammonia, and blood urea were higher for cows consuming the higher protein rations, but particle size had no effect on these criteria of response.

¹ Journal Article No. 3700 of the Oklahoma Agricultural Experiment Station, Stillwater.

² Dairy Extension Specialist, Cooperative Extension Service, Houston, MO.