الملخص الإنجليزي
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 for lactation, 1.60 Mcal/kg DM). Fifty percent of dietary nitrogen was provided by test proteins. Animals were fed four times daily. Chromic oxide holuses, 50 g/day were used to estimate digestion coefficients. Ruminal protein degradability in vivo (%) 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. Ruminal parameters of cows fed SBM vs APC were: pH. 6.6 vs 6.7; ammonia nitrogen (mg/dl), 10.8 vs 6.2 (P < 0.01); total volatile fatty acids (mM), 86.3 vs 84.6 (P < 0.05), acetate (%), 50.8 vs 64.9 (P < 0.01); propionate (%), 24.8 vs 19.6 (P < 0.01); butyrate (%). 10.7 vs 11.5. Digestion coetticients (%) in cows fed SBM vs APC were: dry matter, 65.3 vs 61.8; crude protein, 67.6 vs 61.1 (P < 0.05); neutral detergent fiber, 51.1 vs 52.5; acid detergent fiber, 47.7 vs 49.0. A slightly higher (P> 0.05) amount of milk was produced by cows fed APC (28.6 ± 3.5 vs 28.2 ± 3.8 kg/day). Each additional gram of undegradable intake protein provided by APC contributed to a 5-gram increase in 4% fat-corrected milk production.
