Influence of Roughage-to-Concentrate Ratios on ad Libitum Consumption by Lactating Cows

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Abstract
D libitum consumptions of all-hay, 5.5:1, 2.2::1, and 1:1 weight ratios of alfalfa hay and concentrate mixture fed 84 days were compared with consumption of a 7:4 ratio (control) of hay and con- centrate fed for 50 days before and 24 days following the experimental period. Eight Holstein cows were used for three treatments and nine for the 2ourth. Con- trol ratio hay consumption varied from 2.01 to 2.43 kg per 100 kg body weight (P < .01) over 33 lactations during five years. ~ariation among cows was indicated by coefficients of variation between 10 ~nd 15%. Within year correlation between body weight and hay consumption was 0.38 (P < .05) and within treatment correla- tion between hay consumption in the con- trol and experimental periods was 0.83 (P < .01). Nearly linear replacement of hay by concentrate occurred in the ratio of 0.44 kg hay per kilogram concentrate with the net effect of doubling estimated net energy consumption of the all-hay ra- tion by feeding the 1:1 ratio. Ratios of roughage-to-conc entrate in dairy cow rations that maximize profit depend on available nutrient content of each, their rela- tive prices, and the cow's capacity and feed transformation ability. Since level and economy of lactation depend largely on nutrient intake, the most economical roughage-to-conc entrate ratio is the least expensive one that results in near-maximum energy intake and near- maximum milk production in early lactation