Complete Rations for Dairy Cattle. VI. Percent Protein Required with Soybean Meal Supplementation of Low-Fiber Rations for Lactating Dairy Cows

Three feeding trials were to evaluate effects of protein percent of complete rations as controlled by soybean meal supplementation, on milk production.In Experiment 1, 27 Holstein cows were used to compare 11.5, 13.0, or 14.5% protein rations (air-dry) in a partially balanced incomplete block design in which cows were fed one of the rations in each of two 8-wk periods.Differences of milk yield were small but tended to be higher with higher diet protein.No other parameters (including solids-corrected milk) were affected by treatment.In Experiment 2, 12.0, 14.5, and 17.0% protein rations were fed to 62 Holstein cows during wk 3 through 8 after parturition after their having received the 14.5% ration during the adjustment period 2 wk before and 2 wk after parturition.No effects were due to treatment.In Experiment 3, the 24 highest producing cows of Experiment 2 were used in a Latin square design with three 4-wk periods and rations of Experiment 2 with restriction of feed to 80% of wk-8 consumption during Experiment 2. Again, no differences were due to ration.Little or no benefit could be achieved by soybean meal supplementation of complete rations which contain above 12.0% protein (13.5% of dry matter) with cows producing in lactations which averaged 6370 kg mature equivalent, 305 days.