Animal Nutrition

Corn Plus RPL Can’t Beat SBM and SoyPlus

Dairy farm soy plus product

New research shows that adding rumen protected lysine to lactating cows’ diet can help regain some of the milk yield and milk protein lost when all dietary protein comes from corn. Protein sources, such as corn gluten meal and dried distillers grains with solubles (DDGS), contain less lysine than soybean meal. 

Researchers at the University of Wisconsin compared lactating cows’ performance when diets with similar protein content but different sources of supplemental protein were fed, including one with rumen protected lysine (RPL). The supplemental proteins evaluated include: all soy (10.6 % soybean meal and 21.1% SoyPlus); half soy, half corn (5.3% soybean meal, 10.6% SoyPlus, 8.4% DDGS and 8.4% corn gluten meal); all corn (16.8% DDGS and 16.8% corn gluten meal); and all corn plus RPL (all corn diet plus 125 grams/day of RPL). The RPL was top-dressed immediately after the TMR was fed each morning. Cows were milked twice daily. 

Results show that dry matter intake was highest for cows fed the all soy diet at 61.1 lbs/day. In comparison, cows fed the all corn diet and the corn plus RPL diet consumed about 2 lbs/day less feed. In terms of milk yield, cows fed the all corn diet produced the least amount of milk, 97.7 lbs/day, compared to an average of 101 lbs/day for the other 3 diets. Cows fed the all soy diet had the highest milk protein percentage, 3% yielding 3 lbs of milk protein per day. Milk protein percentage for cows fed the all corn diet was 2.9% compared to 2.97% for cows fed the half soy half corn diet and 2.94% for cows fed the all corn plus RPL diet.

Adding RPL to the all corn diet did recover some of the milk and protein lost from feeding an all corn diet. But it was still short of the production results seen when cows were fed the all soy diet using soybean meal and SoyPlus. 


Lobos et al., 2021. J. Dairy Sci. 104:6620-6632