Response to Concentrates Containing Two Percents of Protein Fed at Four Rates for Complete Lactations

Abstract

Two grain mixes were fed at four rates as a supplement to high-quality alfalfa hay during 305-day lactations of 128 cows. The four rates of concentrates were .25, .375, .50, and .625kg grain per kg of 4% fat-corrected milk above 9.1kg daily. The two mixes were a simple barley and dried beet pulp mix (12% protein) and a more complex 14% protein mix.Increasing the rate of grain caused a linear decrease in hay consumption and a linear increase in intake of grain and total energy and yield of milk and milk constituents. Increasing the grain rate also accounted for a linear increase in percent protein, percent solids-not-fat, but no difference in percent milk fat or total solids. Differences between grain mixes were not significant for any traits except percent milk fat and total solids which were higher on the simple mix. Yield was highly correlated with and followed the pattern of total consumption of net energy for milk production. A stepwise deletion multiple regression analysis found grain intake, rate of grain, hay intake, hay to grain ratio, and length of previous dry period, respectively, the most important variables (squared correlation .94) affecting fat-corrected milk production.