Early Life Nutrition Of Dairy Calves And Its Implications On Future Milk Production

The pre-weaning management of dairy calves over the last 30 years has focused on mortality, early weaning and rumen development. Recent data has demonstrated the potential to influence metabolic programming and consequently alter future performance of dairy cattle through nutrition and management during the first few months of life. Two main management practices have been identified as having the greatest impact in future performance: colostrum management and energy intake pre-weaning. Therefore, the first objective was to investigate the relationship between nutrient intake from milk replacer and pre and post-weaning growth rate with lactation performance. The evaluation of over 1,800 first lactations resulted in a strong relationship between average daily gain (ADG) pre-weaning and milk production so that for every additional kg of ADG pre-weaning first lactation milk production is increased by 850 kg. The relationship is equally strong when assessed by energy intake above maintenance from milk replacer during the pre-weaning period. The second objective of this work was to evaluate the effects of preweaning nutrition on mammary gland development. The mammary gland, especially the parenchymal mass were shown to be responsive to nutrient intake such that the parenchymal mass of calves that consumed more nutrients grew 5.6 times faster than that of control calves. This was significant because it demonstrated that allometric growth can be initiated from birth and that the mammary gland is very nutrient responsive, something not readily recognized in dairy cattle. The interaction of colostrum status and pre-weaning nutrient intake was also evaluated and the data suggests that the effects of colostrum management can be amplified or muted depending on nutritional status pre-weaning. Colostrum contains an array of different growth factors that can account for some of the long-term impacts on growth and efficiency; a preliminary study evaluating hormone levels post-colostrum feeding in newborn calves suggest that hormones present in colostrum may be directly absorbed by the calf and could impact metabolic programming through the "Lactocrine hypothesis". Protein synthesis and accretion is proposed as the primary signal that enhances future performance of pre-weaned cattle; however, milk protein sources are expensive and feeding high levels of such proteins may not always be cost effective. Therefore, alternative protein sources were evaluated as a way to reduce the cost of milk replacers. In this study, milk replacers containing whey based protein were the most effective milk replacers, with or without a modified amino acid profile