Influence of Three Ratios of Silage and Grain and Corn versus Beet Pulp on Voluntary Intake by Dairy Heifers

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Abstract
Silage alone and silage to corn or beet pulp ratios of 80:20, 60:40, and 40:60 (dry matter basis) were fed to dairy heifers and fistulated steers to study the inter-re- lationships between ration composition, tu- reen fermentation, and voluntary intake of dry matter and estimated net energy. The silage was a wheat plus ryegrass mix- ture. When corn was fed, dry matter in- take was not improved over the 80:20 ratio by higher levels of substitution. The same trend occurred with beet pulp, except that the maximum level of 40:60 reduced intake to a level similar to silage alone. Due to increased ration digestibility, the two feeds resulted in similar and consistent increases in estimated net energy intake at each level of substitution. Multiple regres- sion analysis indicated that the relation- ships between ration composition and intake were complex, involving a delicate balance between cellulose, nitrogen-free extract, rate of rumen fermentation, and bulk den- sity of the ration.