Effects of the addition of starch on the utilization by sheep of the protein and crude fibre contained in lucerne hay and soya-bean meal

Abstract

SUMMARYA sheep-feeding experiment was carried out to compare the influence of starch supplementation on the utilization of protein contained in a roughage (lucerne hay) and in a concentrated feed (soya-bean meal). Twelve young rams were divided into four groups, all of which received 150% of the theoretical protein requirement for maintenance. Two groups received soya-bean meal, and the two other groups were given alfalfa hay as protein source. One soya-bean group and one lucerne hay group served as control groups and received the theoretical requirement of energy, whereas the energy content of both experimental groups was raised by addition of grain to 150% of the theoretical energy requirement.A N-balance experiment carried out with both control groups did not indicate the superiority of lucerne hay over soya-bean meal as had been found in previous experiments in which the sheep were fed diets just supplying the theoretical protein requirement. The advantage of roughage protein disappeared as a result of changes of dietary regime, such as the ingestion of protein surpluses and the reduction in the amount of cottonseed hulls.The N retention from the lucerne-hay ration was enhanced much more than the soya-bean meal ration by the addition of maize. Biochemical analyses of the rumen oontent showed that a much higher metabolic activity of the micro-organisms was induced by feeding a lucerne-hay diet supplying 150% of the theoretical protein requirement than that induced by ingestion of a corresponding amount of soya-bean meal. It was concluded that the increased biochemical potential of the lucerne-hay diet could be used advantageously only in presence of ample amounts of soluble carbohydrates. The digestibility of the carbohydrates contained in all four diets was examined by in vivo and in vitro methods. The digestibility of crude fibre in the lucerne-hay ration was somewhat raised by the addition of maize whereas the digestibility of crude fibre in the soya-bean meal ration was considerably depressed by the addition of maize.The digestibility of the carbohydrates contained in all four diets was examined by in vivo and in vitro methods. The digestibility of crude fibre in the lucerne-hay ration was somewhat raised by the addition of maize whereas the digestibility of crude fibre in the soya-bean meal ration was considerably depressed by the addition of maize.