Feeding the young ruminant

Abstract

AbstractYoung calves and lambs are weaned early to reduce the amount of milk products consumed and potentially improve the profitability of rearing enterprises. At weaning the pre-ruminant must make a number of adjustments to cope with the change in dietary substrate. The microbial population in the rumen must develop and metabolic changes are required in order for the young ruminant to metabolize the end products of microbial digestion. It is recognized that early weaning poses a stress to the calf but it is generally considered that the calf rapidly adjusts to the change in diet composition. A number of factors indicate that considerable advantage would be gained from delaying the weaning of calves and indeed that the calf is not physiologically capable of adapting to an early-weaning regime. Work has indicated that a diverse anaerobic microbial population can be identified in the developing rumen of the calf. More recent results show that the presence of a faculative anaerobic population, which exists for a considerable period of time, has an adverse effect on the development of a mature anaerobic population. Low rumen pH is a problem in the young calf. The level of rumen pH verges on that which would be described as acidosis in the adult ruminant. The young calf is unable to stabilize rumen pH and increasing the level of dry food intake at weaning may further depress rumen pH if the salivary buffering capacity of the calf is not adequately developed. Results indicate that the ability to utilize volatile fatty acids is not fully developed in the young calf and that early weaning can result in high levels of VFAs in the circulation.The composition of the dry diet has a major effect on the response of the calf to weaning. Choice of the ingredients can affect the buffering capacity of the rumen and the physiological development of the digestive tract. Strategies to limit the nutrient intake from dry food to levels commensurate with the developing physiology of the calf may result in a more uniform transition to full ruminant status with consequent benefits in growth rate and health.