Isoacids and Urea as a Protein Supplement for Lactating Cows Fed Corn Silage

Abstract

We studied effects of isoacids (isobutyrate, isovalerate, 2-methylbutyrate, and valerate) on milk production when com silage was the sole roughage for 98 lactating cows in four trials. In the first trial isoacids plus phenylacetate (100 g) were fed with urea (300 g) to 24 lactating cows in a randomized block design with a soy protein control, urea control, and urea plus isoacids and phenylacetate treatment. Concentrate was not fed. Soy protein was most effective in maintaining milk production, persistency of lactation, and body weight. Isoacids improved milk production, persistency of lactation, and body weight over the urea alone. In the second trial, corn silage and corn grain were fed to 28 lactating cows in a randomized block design with a positive control (soybean meal), a negative control (no nitrogen supplementation), urea, or urea plus isoacids. Concentrate was fed according to milk production (1 to 2.5 kg). Isoacids improved persistency of lactation over the urea control. For the third trial, 18 lactating cows were in a crossover design with a urea control treatment, and urea plus two mixtures of isoacids. Isoacid mixture 1 contained, on a molar basis, 28, 24, 24, and 24% isobutyrate, isovalerate, 2-methylbutyrate, and n-valerate, respectively. The corresponding percents for mixture 2 were 36, 17, 17, and 30%. The addition of isoacids to urea improved persistency of lactation and milk production and decreased urea nitrogen in plasma and ammonia nitrogen in the rumen. In the fourth trial, 28 lactating cows were paired in a 90-day continous feeding trial. Concentrate was fed according to milk production. Cows were fed a urea control treatment and urea-isoacid mixture 1. Isoacids improved persistency of lactation. © 1980, American Dairy Science Association. All rights reserved.