Body Composition of Dairy Cattle by Potassium-40 Liquid Scintillation Detection

Liquid scintillation detection by potassium-40 was used to estimate body composition of dairy cows of two ages and two yields. Average body weight, fat content, and protein content were 548 kg, 27%, and 17%. First-calf cows had less body weight, less protein mass, and less fat mass than older cows, suggesting that heifers in first lactation continue to deposit protein and fat in later lactations. Production had no effect upon estimates of body composition. In response to lactation needs, there were average losses of about 50 kg of fat and about 10 kg of protein with marked variation among animals. Procedures preparatory to potassium-40 monitoring had no effect upon milk production. For estimating body composition in dairy cows liquid scintillation using potassium-40 detection appears to be nontraumatic and highly repeatable.