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

Lactation and balance studies were carried out with 12 Holstein cows in a randolnized complete block design. Twenty, forty, or sixty per cent of the estimated net energy (ENE) was supplied in the form of hay; the remainder in the forln of concentrate. The level of ENE intake above maintenance was held constant. FCM production was approximately the same for all groups. A significant and rectilinear increase in pounds of FCM per therm of digestible energy consumed above maintenance was observed as the proportion of concentrates in the ration increased. Digestibility data are presented. Urinary energy losses were closely correlated (r = 0.96) with urinary nitrogen losses.