Effect of the Net Energy Concentration of Total Ration on Milk Production and Composition

Eighteen Holstein cows were assigned, after a 17-day preliminary period, to three rations, using a double 3 3 Latin-square design. The pounds of alfalfa-orchard grass hay and corn silage offered each cow during the experimental periods were, respectively: Ration A--6, 24; Ration B--1O, 40; Ration C--14, 56. Concentrate was added to each ration so that total feed energy offered supplied maintenance needs plus 0.39 therm estimated net energy per pound 4% FCM. Each experimental period was 4 wk, the last 3 wk being used to evaluate ration effects. Average daily intakes of hay, silage, and concentrate, respectively, for the rations were: A--5.6, 23.3, 26.6 lb; B--8.5, 36.4, 20.5 lb; C--10.9, 45.9, 14.6 lb. Average 4% FCM was 46.7, 46.2, and 43.8 lb daily for Rations A, B, and C, respectively. Milk production on Rations A and B was significantly higher (P < .01) than on C, but gross and net efficiencies were essentially the same for all rations. There was a significant increase (P < .05) in SNF with increasing proportions of concentrate in the ration. There was no depression of fat level in milk on any of the rations. Cows on Ration C gained the most weight, but weight changes on all rations were small, suggesting that the level of feeding employed herein approximated the needs of the animals.