Effect of Graded Levels of Soybean Meal and of a Nonprotein Nitrogen-Molasses Supplement on Consumption and Digestibility of Wheat Straw

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Abstract
A study was made of the voluntary intake of wheat straw by cattle fed soybean meal (trial 1) or a liquid supplement (trial 2) containing urea and ammonium polyphosphate as nonprotein N sources in a molasses base. Supplementary crude protein was fed at 0, 1, 2, 3 or 4 g crude protein/kg BW.75 /day. Digestibility data were obtained by means of fecal grab samples, with lignin used as an internal indicator. Voluntary intake of wheat straw was increased (P<.05) by the addition of 1 g or more of soybean meal protein, but no statistical increase was observed when the liquid supplement was fed. Apparent digestibility of crude protein was negative when wheat straw was fed alone. The addition of 1 g of crude protein from soybean meal or liquid supplement increased crude protein digestibility markedly; digestibility continued to increase before plateauing at 3 or 4 g of supplemental crude protein, regardless of the N source, although coefficients were higher when soybean meal was fed. Some of these differences might have been caused by differences in the crude protein content of the straws used in trials 1 and 2. Dry matter and acid detergent fiber digestibilities also were increased by N supplementation, regardless of source, but maximum increases were observed at the 1-g level. Correlation coefficients generated from the data indicated that crude protein consumption had a stronger effect on straw consumption when N was supplied by soybean meal. In addition, crude protein digestibility was more highly correlated with consumption of straw and digestible energy when soybean meal provided the N. Voluntary consumption of digestible energy was improved by the feeding of soybean meal, but not by the feeding of liquid supplement. Energy consumption of cattle fed soybean meal protein at the 1-g level or higher was sufficient to meet or exceed maintenance needs, but cattle fed liquid supplement did not consume enough digestible energy to maintain body weight. Copyright © 1982. American Society of Animal Science . Copyright 1982 by American Society of Animal Science

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