Response of lactating dairy cows to steam-flaked sorghum, steam-flaked corn, or steam-rolled corn and protein sources of differing degradability

Protein sources with different degradabilities were fed to 48 lactating Hol stein cows receiving 37 or 39% of dietary dry matter as steam-flaked sorghu m (360 g/L), steam-flaked corn (360 g/L), or steam-rolled corn (490 g/L) in a 3 x 2 factorial arrangement of treatments. Cows were fed an alfalfa-base d diet with 7% soybean meal or 5% of an animal-marine protein blend and 37 or 39% grain. Although not significant, cows fed flaked grain yielded a mea n of 1.5 kg/d more milk than did those fed rolled grain. Gross feed efficie ncy was not affected by grain processing or protein source, but diets with the animal-marine protein blend had 9% higher estimated net energy for lact ation than did diets with soybean meal. The greater gains in body weight an d increased digestibility of the diets with the animal-marine protein blend verify the higher energy concentration of those diets. Yield of milk prote in was increased by flaked grain or the animal-marine protein blend, and fl aked grain increased percentages of lactose and solids nonfat. Increasing t he ratio of rumen-degradable starch to rumen-degradable protein increased m ilk protein content and yield linearly and increased contents of lactose an d solids nonfat. A linear response of dry matter, organic matter, crude pro tein, and starch digestibilities was observed as the ratio of rumen-degrada ble starch to rumen-degradable protein increased. These data show improved performance of dairy cows fed a high rumen-undegradable protein source with diets high in rumen-degradable starch from steam-processed grains.