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Abstract
Ten multiparous Holstein cows were used in a 105-day continuous feeding trial to compare soybean meal (SBM) and alfalfa protein concentrate (APC) as supplemental protein sources for high-producing dairy cows. Dairy cows with an average milk production of 35.2 kg/day were paired and randomly assigned to one of the treatments. A double reversal design was employed With 35 days per period. The comparison between treatments was made during the last 21 days of each period. Experimental diets, containing 60% corn silage and 10% alfalfa hay, were formulated to be isonitrogenous and isoenergetic (crude protein. 15.6%; net energy tor lactation, 1.60 Mcal/kg DM). Fifty percent of dietary nitrogen was provided by test proteins. Animals were fed four times daily. Chromie oxide boluses, 50 g/day were used to estimate digestion coefficients. Ruminal protein degradability in viva (%) and in situ(%)were 56.8, 68.3 and 47.3. 35.3 for SBM and APC, respectively. Dry matter intake (kg/day) was 19.1 and 18.6 for cows fed SBM and APC. respectively. Rummal parameters cows fed SBM vs APC were, pH. 6.6 vs 6.7, ammonia nitrogen(mg/dI) 10.8 vs 6.2(p less than 0.01); total volatile fatty acids (mM), 86.3 VS 84.6(P LESS THAN 0.05), acetate (%) , 50.8 vs 64.9 (p less than 0.01); propionate dry matter , 65.3 vs 61.8; crude protein . 67.6 vs 61.1 (P less than 0.05 ) neutral detergent fiber , 51.1 vs 52.5 ; acid detergent fiber, 47.7 vs 49.0 . A slightly higher (P more than 0.05 ) amount of milk was produced by cows fed APC(28.6+_ 3.5 vs 28.2+- 3.8 kg/day). Each additional gramof undergradable intake protein provided by APC continued to a 5- gram increase in 4% fat-corrected milk production.