LAUSR

Abstract Optimal protein nutrition of dairy cattle is important to support efficient production of high producing lactating dairy cows. Canola meal (CM) and corn dried distillers’ grains with solubles (DDGS) have been primary protein meals on many dairy farms in the Western USA for over 10 years, but decreases in the relative price of soybean meal (SBM) has created interest in how best to include it in lactation diets containing CM and DDGS. Three pens of ˜310 high producing multiparous Holstein cows were fed diets supplying 0, 35 or 70 g/kg SBM on a dry matter (DM) basis, which largely replaced CM, in a way that held the proximate nutrient content of the diets constant. Diets were rotated through the pens in a Latin square design such that each pen of cows experienced each diet once. Milk and component yields were lowest at the highest SBM level (Quad P