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In trial 1, eight Holstein heifers weighing 410 kg were used in an 8 x 8 Latin square and fed TMR containing 79.3% alfalfa silage and 20% soybeans. The first four treatments were raw soybeans, soybeans roasted and held for 3 h at the roasting temperature, extruded soybeans, and soybeans roasted in a California Pellet Mill Jet-Sploder. The remaining four treatments were obtained by altering the residence time of soybeans in the Jet Sploder. The temperatures of soybeans exiting the roaster were 117, 126, 138, and 154 degrees C for the last four treatments. The soybeans held 3 h postroasting and the extruded soybeans resulted in the highest estimate of postruminal available lysine. Blood plasma concentrations of essential and branched-chain AA were highest in heifers fed soybeans held 3 h postroasting. In trial 2, 44 Holstein heifers weighing 150 to 250 kg were assigned randomly to one of four TMR. Diets consisted of 91.8% alfalfa silage and 7.5% of one of four soybean treatments. Treatments were raw soybeans, soybeans roasted in a drum roaster with an exit temperature of 146 degrees C, and those roasted with exit temperatures of 141 or 146 degrees C and held for .5 h. Estimated postruminal available lysine was higher for soybeans roasted and held versus roasted or raw soybeans. However, BW gain for heifers was similar across diets, averaging .90 kg/d for 12 wk. Concentrations of AA in plasma were not affected by diet. Overall, results support the recommendation of holding soybeans for at least .5 h following roasting.

Soybeans were heated in a forced air oven at 120 and 130 degrees C for 60 and 180 min, and at 140, 150 and 160 degrees C for 10, 30, 60, 90 and 120 min. Two types of measurements were used to determine optimal heat treatment of soybeans to maximize protein utilization by ruminants. One was to estimate the rate and extent of protein degradation in the rumen using an in vitro ruminal system. The second was to determine the nutritional availability of lysine. Methods used to determine available lysine were an indirect fluorodinitro-benzene chemical method and a rat growth assay. The product of undegraded intake protein and available lysine content was used to estimate the amount of lysine that would escape ruminal degradation and be available for intestinal absorption. As heat input increased, ruminal undegraded intake protein increased, and protein degradation rates and total and available lysine decreased. As temperature increased, the time required to maximize post-ruminal available lysine decreased. The optimal heat treatment for soybeans heated in a forced air oven was: 140 degrees C for 120 min or greater, 150 degrees C for 60 min or 160 degrees C for 30 min. A loss of 15-22% of chemically determined available lysine was necessary to achieve the heat treatment that resulted in maximal post-ruminal available lysine.

Forty-six multiparous Holstein cows were fed one of three total mixed diets from 15 to 119 d postpartum with alfalfa silage as the only forage. Each diet contained 50% forage and 50% concentrate on a DM basis. Diets were formulated to be isonitrogenous by replacing corn and solvent soybean meal with raw soybeans or heat-treated soybeans. The proportion of protein supplement in the diet on a DM basis was 10% soybean meal, 13% raw soybeans, or 13% heat-treated soybeans. The soybeans were heat-treated to maximize the amount of available lysine passing to the small intestine. The soybean meal diet was fed to all cows during wk 1 and 2 postpartum for covariate adjustment of DMI and milk production. Intake of DM was similar across treatments. Feeding heat-treated soybeans supported more milk (4.5 kg/d), 3.5% FCM (4.0 kg/d), and milk protein (.09 kg/d) than soybean meal or raw soybeans. Milk fat percentage was not altered by treatments. However, milk protein percentage was depressed in cows fed heat-treated soybeans compared with soybean meal (2.85 vs. 2.99%, respectively). Milk production response of cows fed properly heat-treated soybeans compared with soybean meal with alfalfa silage as the sole forage is thought to be related primarily to improved supply of undegraded intake protein.

Effects of different amounts of wheat, protected amino acids, and increased rumen escape protein in high wheat rations were evaluated in two trials with dairy cows. In trial 1, concentrate mixtures with 0, 40, or 60% hard red winter wheat were included in a complete ration with 45% sorghum silage (dry basis). Intake of DM and CP was not affected by treatment. Milk yield declined (28.8, 28.0, 27.3 kg/d) as amount of wheat in the ration increased. In a second trial, concentrate mixtures with 60% wheat were compared with a control corn-base mixture. One wheat mixture was supplemented with protected lysine and methionine and another had protected lysine and methionine plus estimated rumen escape protein equal to the control. Intake of DM and CP was not affected. Milk yield of cows fed rations containing wheat, with or without protected amino acids, was lower than that of cows fed the control ration or the wheat ration in which rumen escape protein was equal to the control (29.1 and 29.0 vs. 30.8 and 30.2 kg/d). Responses of cows fed concentrate mixtures containing wheat appeared to be related to utilization of protein.