Effect of Whey on Milk Composition and Rumen Volatile Fatty Acids in Restricted-Roughage Rations

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Abstract
In two trials lactating Holstein cows were fed rations of 16% hay and 84% concen- trate at 120% of the Morrison Standard for energy. Concentrates contained varying amounts of partially delactosed whey (PDW) and dried whole whey (DWW). Per cent fat in milk was maintained at pretreatment levels when as little as 10% PDW was incorporated into the concen- trate. At the 30% level, the DWW was not as effective in maintaining milk fat as was PDW. Neither milk SNF nor protein was consistently affected by addition of whey. Milk yields were depressed when the concentrate contained 60% of either whey, but not at 30%. All concentrates were readily consumed by the cows. Molar per cent of tureen butyrate was increased by addition of both kinds of whey at all levels tested. These increases were probably due to the lactose in whey. Rumen propionate was decreased and acetate-to-propionate ratios increased by addition of PDW, bu~ not by DWW. The increased tureen butyrate and acetate- to-propionate ratios, as well as the de- crease in rumen propionate, were asso- ciated with maintenance of normal milk fat percentages in groups fed rations contain- ing PDW.