Twelve multiparous Holstein cows averaging 57 d (36 to 77 d) postpartum at the start of the experiment were utilized in a replicated 4 x 4 Latin square design. Dietary protein supplements were 1) soybean meal, 2) soybean meal plus ruminally protected Lys and Met, 3) corn distillers grains, and 4) corn distillers grains plus ruminally protected Lys and Met. Dry matter intakes were lower for cows fed diets containing soybean meal than for cows fed diets containing corn distillers grains. Milk yield increased with the corn distillers grains (34.3, 34.0, 35.3, and 36.7 kg/d for cows fed diets 1 through 4, respectively), especially when supplemented with ruminally protected Lys and Met. Milk protein yield and percentage were increased by amino acid supplementation. Milk fat yield and percentage were unaffected by diet. The only milk protein fraction affected was nonprotein N, which was lower in the milk of cows fed corn distillers grains. Lysine, Met, and Phe were indicated as the most limiting amino acids for all diets when using amino acid extraction efficiency and transfer efficiency to indicate limiting amino acids. When corn distillers grains were supplemented with ruminally protected Lys and Met, milk yield and milk protein yield and percentage increased because the diet containing corn distillers grains was probably deficient in Lys.

Four ruminally cannulated Holstein cows in midlactation were randomly assigned to a 4 x 4 Latin square design with a 2 x 2 factorial arrangement of treatments to evaluate two nonstructural carbohydrate sources (corn or barley) with two sources of ruminally undegradable protein (soybean meal or extruded soybean meal) on milk production, ruminal fermentation, and digesta passage rates. Milk production (25.1, 27.5, 23.8, and 23.5 kg/d for the corn and soybean meal, corn and extruded soybean meal, barley and soybean meal, and barley and extruded soybean meal, respectively) and dry matter intake per unit of body weight (3.9, 4.1, 3.7, and 3.7%) were greater for cows fed corn than for cows fed barley and were similar for cows fed soybean meal or extruded soybean meal. Concentrations of ruminal NH3-N were greater for cows fed the corn and soybean meal diet than for cows fed other diets (15.0, 10.4, 9.0, and 11.3 mg/dl). Rumen volatile fatty acid concentrations were greater for cows fed corn than barley (133, 139, 121, and 118 mumol/ml). Fractional passage rates of solids from the rumen were greater for cows fed the barley and soybean meal diet than cows fed the corn and soybean meal diet (3.4, 3.9, 4.2, and 3.8%/h), and ruminal liquid dilution rates were similar for cows fed all diets (11.2, 11.0, 11.1, and 11.9%/h). The attempt to synchronize ruminal nonstructural carbohydrate and crude protein degradability produced minimal benefits for midlactation dairy cows.

Two ruminally cannulated Holstein cows (approximately 202 DIM) were used to determine the in situ degradability of five protein supplements: blood meal, meat and bone meal, corn gluten meal, expeller soybean meal, and solvent extracted soybean meal. Dacron bags containing 4 g of each supplement in duplicate were soaked in water and then incubated in the rumen for 0, 3, 6, 12, 18, and 24 h for 3 d. Four extra sample bags of each supplement were incubated in the rumen for 12 h to determine the in vitro intestinal digestibility and AA analysis of the residues. Protein supplements were also analyzed for their AA content. Ruminal degradability of individual supplements varied. Solvent soybean meal was the most degradable, and blood meal was the least degradable. Specific first-limiting essential AA were isoleucine for blood meal and meat and bone meal, lysine for corn gluten meal, and methionine for the soybean meals. The RUP fraction in solvent-extracted and expeller soybean meals tended to be more intestinally digestible than did the protein in blood meal and meat and bone meal. In general, all protein supplements, except solvent-extracted soybean meal, were high in RUP and had the potential to provide good quality AA to complement microbial AA for production.

Holstein calves were used wk 1 to 12 after birth to evaluate three sources of nonstructural carbohydrates that differed in ruminal degradability (corn, barley, and dried whey) with two sources of CP (normal and extruded soybean meal) that also differed in ruminal degradability. Nonstructural carbohydrates were most degradable in the dried whey diets and least degradable in the corn diets, and protein was more degradable in soybean meal than in extruded soybean meal. Pelleted diets were formulated to be isonitrogenous at 18% CP and contained (DM basis) 20% ground alfalfa hay, the respective carbohydrate and protein sources, vitamins, minerals, and antibiotic premix. All calves received 4.5 kg/d of milk during wk 1 to 4 and 2.3 kg/d during wk 5. The BW gains during wk 1 to 12 were higher (.80, .70, and .70 kg/d) for calves fed corn than for those fed barley and dried whey, respectively, and were slightly higher for calves fed extruded versus normal soybean meal (.76 and .71 kg/d). Corresponding DMI (1.47, 1.34, and 1.31 kg/d) were higher for calves fed corn than for those fed barley and dried whey and were higher for calves fed extruded versus normal soybean meal (1.43 and 1.32 kg/d). Trends in BW gains and feed intakes for wk 1 to 5 and 6 to 12 were similar. Feed to gain ratio was similar for all diets in all periods. The BW gains of calves tended to be greater when they were fed diets containing nonstructural carbohydrates and protein that was less ruminally degradable.

Thirty-five 3-mo-old 150-kg Holstein heifers were fed diets containing two nonstructural carbohydrate sources (corn or barley) with two quantities of undegradable protein (soybean meal or extruded soybean meal) for 9 wk in a 2 x 2 factorial arrangement to evaluate NRC guidelines that the diet contain increased quantities of undegraded intake protein. Total mixed diets fed for ad libitum intake contained approximately 17.4% CP, consisting of 16.7% corn silage (DM basis), 33.3% chopped alfalfa hay, and 50% concentrate mix. Average daily gains were greater for heifers fed extruded soybean meal, but response was greater when heifers were fed barley-extruded soybean meal (1.12, 1.13, 1.05, and 1.23 kg/d for corn-soybean meal, corn-extruded soybean meal, barley-soybean meal, and barley-extruded soybean meal, respectively) than diets of barley-soybean meal. Extruded soybean meal increased DMI (5.9, 6.1, 5.2, and 6.7 kg/d), but DMI were similar when diets based on corn or barley were fed. Diets with greater concentrations of undegraded intake protein fed to dairy heifers resulted in greater DMI and average daily gains, but responses were greater when heifers were fed diets based on barley rather than corn. These results suggest that current NRC recommendations for undegraded intake protein fed to 3- to 6-mo-old dairy heifers are too high; diets containing 35 to 40% undegraded intake protein should be sufficient.