Effect of Feeding Different Ratios of Roughage to Concentrate upon Milk Production and Digestibility of the Ration

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Abstract
A randomized block design was used to study the productive and digestive efficiency of cows consuming rations containing 80, 60, and 40% dry matter from roughage and the balance from concentrates. Twelve animals were used and the experimental period was 112 days in length. Digestibility trials, involving total fecal collections were conducted at about the 10th and 20th weeks of lactation. In addition, 8 dry cows were used for obtaining digestibility values on the roughage portion of the ration. As the proportion of concentrate in the ration became larger the apparent digestibility coefficients of the mixed ration increased for dry matter, crude protein, ether extract, N-free extract, and total carbohydrates (crude fiber plus N-free extract). Total digestible nutrient and dry matter intakes also increased. The apparent digestibility of crude fiber decreased as the proportion of concentrate in the ration increased. There was no significant difference in the average amounts of milk produced by the animals consuming the different rations. Efficiency of milk production, expressed as pounds of total digestible nutrients per pound of 4% fat-corrected milk produced decreased as the proportion of concentrate in the ration increased. The data support other reports which suggest that present U.S. feeding standards for dairy cattle are not as accurate at high or low levels of production as at medium levels, and that they are more accurate with usual rations than with very high proportions of either concentrates or roughage.