Soybean Meal - Dairy

An incomplete 8 x 8 Latin square trial (4-wk periods; 12 wk total) using 48 Holstein cows was conducted to assess the production response to crude protein (CP), digestible rumen-undegraded protein (RUP), and rumen-protected methionine (RPM). Diets contained 21% alfalfa silage, 34% corn silage, 22 to 26% high-moisture corn, 10 to 14% soybean meal, 4% soyhulls, 2% added fat, 1.3% minerals and vitamins, and 27 to 28% neutral detergent fiber on a dry matter (DM) basis. Treatments were a 2 x 2 x 2 factorial arrangement of the following main effects: 15.8 or 17.1% dietary CP, with or without supplemental rumen-undegraded protein (RUP) from expeller soybean meal, and 0 or 9 g of RPM/d. None of the 2- or 3-way interactions was significant. Higher dietary CP increased DM intake (1.1 kg/d), yield of 3.5% fat-corrected milk (2.2 kg/d), fat (0.10 kg/d), true protein (0.05 kg/d), improved apparent N balance and digestibility of DM and fiber. However, milk urea N and estimated urinary excretion of urea-N and total-N also increased, and apparent N efficiency (milk-N/N-intake) fell from 33 to 30% when cows consumed higher dietary CP. The positive effects of feeding more RUP were increased feed efficiency and milk fat content plus 1.8 kg/d greater fat-corrected milk and 0.08 kg/d greater fat, but milk protein content was lower and milk urea N and urinary urea excretion were elevated. Supplementation with RPM increased DM intake (0.7 kg/d), fat-corrected milk (1.4 kg/d), fat yield (0.06 kg/d) and tended to increase milk fat content and yield of milk and protein.

Broderick GA, Stevenson MJ, Patton RA. 2009. Effect of dietary protein concentration and degradability on response to rumen-protected methionine in lactating dairy cows. J Dairy Sci. 92(6):2719-28.