Effect of the Dietary Ratio of Hay to Concentrate on Milk Production, Ration Digestibility, and Urinary Energy Losses

Abstract

Lactation and balance studies were carried out with 12 Holstein cows in a randomized block design. Of the estimated net energy intake 20, 40, or 60% was supplied as hay; the remainder as concentrate. The intake of estimated net energy above maintenance requirements was the same for all cows, and was held constant during the 14-week experimental period. Average daily fat corrected milk production was approximately the same (45.8, 46, 44.3 lbs.) in the 3 groups. As the proportion of concentrates in the ration increased, the efficiency with which digestible energy was utilized for milk production increased in a rectilinear manner. Differences among treatments were significant (P<0.05). The apparent digestion coefficients for dry matter, ether extract, nitrogen-free extract and gross energy also increased significantly (P<0.01); while those for crude fiber and crude protein were not significantly affected by the ratio of hay to concentrate. Urinary energy losses were closely correlated (r = 0.96) with urinary nitrogen losses.