91. The influence of birth weight on dairy Holstein heifer calf health and growth prior to weaning

Application: It's essential to support successful growth of dairy calves to ensure efficient and profitable production systems. Lower birth weight calves should be managed separately, allowing for farmer intervention to minimise health challenges experienced and support growth. Introduction: A critical issue for the dairy industry is achieving target growth rates in dairy calves, which affects the age at first calving for dairy heifers and has financial repercussions. Neonatal calf diarrhoea and enteric infections are among the main causes which can be as a consequence of insufficient calf growth and/or stress in early life. It was found that calves experiencing any form of disease had significantly higher mortality rates. According to the AHDB Dairy Calf to Calving project, most farms are not achieving heifer growth targets, with 70% of farms under target at weaning. This study aimed to assess if birth weight influenced number of health challenges experienced during pre-weaning and if this subsequently affected final weight at weaning. Materials and methods: Holstein heifer calves (n = 16) from Hartpury Home Farm were separated from dams at birth and housed individually. Colostrum was fed at 10% birth weight within 4hours followed by 2L of GLW Lifetime Elite milk replacer (17% oil, 26% protein) feed twice daily. Calves were moved to group pens (n = 14) at 1 week old and group fed to weaning (mean age 84 days). Calf starter was offered ad libitum. Calf weights and average daily gains were tracked via the calf unit recording system. Challenges were recorded and included periods when medical intervention was needed (high temperature, diarrhoea, enteric infection, nasal/ocular discharge). Data was analysed using SPSS (version26). Shapiro-Wilk normality test was conducted. A linear regression was used to assess whether birth weight influenced number of challenges experienced and if this significantly predicts weight post-weaning. Model selection via linear regression was set at P < 0.05. Results: Lower birth weight calves (30–35 kg) experienced more challenges than those with high birth weight (Figure 1) prior to weaning. Average daily gain was also reduced as a consequence (Table 1). The linear regression model was significant, explaining 35% (R2 = 0.348) of the variance between birth weight and number of challenges and explaining 34% (R2 = 0.339) of the variance between the number of challenges and final weight at weaning (Table 2) (Figure 2). Conclusion: Dairy calves with lower birth weights experienced more challenges over the pre-weaning period, with average daily gains reduced. Thus, having an effect on final weights post-weaning. R2 values were low indicating birth weight and challenges as limited predictors of calf health and final weight. However birth weight was seen to be a better predictor of challenges.