GROWTH OF DIGESTIVE ORGANS AND THEIR CONTENTS IN HOLSTEIN STEERS: RELATION TO BODY WEIGHT AND DIET

Abstract

Holstein steers given concentrate or roughage diets were slaughtered at 60, 100, 200, 300, 400, or 500 kg liveweight. Their gastrointestinal tracts were separated into reticulo-rumen, omasum, abomasum, and intestine, emptied of digesta and weighed. Growth of organs relative to growth of the empty body as a whole was described by the allometric equation (Y = aXb). Relative growth rates of the organs were greater than that of the empty body during transition from milk to a solid diet, and less than that of the empty body (b < 1) after the transition. Post-transition growth rate of the reticulo-rumen was greater than that of the other organs. Diet had no effect on weights of reticulo-rumen, abomasum, or intestine, but omasa of hay-fed steers were heavier than those of concentrate-fed steers. Weight of digesta increased substantially during transition to full anatomical development of the gastrointestinal tract, and thereafter continued to increase in all organs except the abomasum. Hay-fed steers had more digesta in the reticulo-rumina, omasa, and intestines and the digesta had a lower percentage of dry matter than in concentrate-fed steers. Within diets, total digesta dry matter in the entire tract, the reticulo-rumen, and the intestine was proportional to dry matter intake, and it was suggested that development of a prediction equation for estimating digesta from dry matter intake might be possible if more information were obtained on how differences in the amount and nature of diet and the time elapsed since the previous meal affect weight of digesta. Key words: Cattle, diet, digesta, digestive tract, growth