Preweaning Nutrition and Its Effects on the Growth, Immune Competence and Metabolic Characteristics of the Dairy Calf

SIMPLE SUMMARY: The rearing of replacement heifers is arguably a dairy farmer’s most important investment and one of the leading expenses on dairy farms. Australian calf rearing recommendations have changed very little in the last 30 years, with recent studies considering them inadequate. Early-life nutrition is widely understood to affect the development of physiological systems in all species; it is therefore essential that effective calf rearing strategies are in place to produce resilient cows to ensure a productive and profitable dairy industry. This experiment followed 20 heifer calves from birth to weaning and investigated the effects of two preweaning nutritional strategies (Low: 4 L or High: 8 L of milk per day) on growth, immune competence, and metabolic characteristics. The physiological systems were compared between treatments in response to an immune challenge in the form of a vaccination. Calves fed a higher milk volume in the preweaning phase had superior growth, immune and metabolic characteristics than calves on the restricted milk diet. Therefore, these results do not support the current industry practice of restricted milk feeding calves. Developments in this area could provide new management approaches improving health, welfare and profitability in the dairy industry. ABSTRACT: Feeding increased volumes of milk in the preweaning phase has been shown to improve growth, morbidity and mortality rates in calves (Bos Taurus). This experiment enlisted 20 Holstein-Friesian dairy replacement calves from birth until weaning (at 10 weeks of age) and assessed the effect of feeding either 4 L (Low) or 8 L (High) of milk per calf per day on their growth, immune competence and metabolic characteristics. The responsiveness of these systems was compared through a vaccination immune challenge. Calves in the High treatment group were significantly heavier from two weeks of age and were 19 kg heavier than calves in the Low treatment group at weaning. Calves in the High treatment group also exhibited greater immune responses, with significantly higher white cell counts and neutrophil counts than calves in the Low treatment group post-vaccination. Calves in the High treatment group also had lower beta-hydroxybutyrate both pre- and post-vaccination, and higher glucose and insulin levels post-vaccination, indicating superior metabolic characteristics. Calves had ad libitum access to lucerne hay (Medicago sativa) and a commercial concentrate. Solid feed intakes were mostly the same between treatments, with differences in hay intake only detected at 7 and 8 weeks of age. Results from this experiment are indicative of a positive influence of accelerated preweaning nutrition on growth, immune response and metabolic characteristics.