The effect of early life events on lactation and reproductive performance in dairy heifers

© 2016 Dr. Gemma ChuckThe main objective of this study was to determine if early life events of dairy heifer calves were associated with subsequent reproductive and lactation performance under typical management systems used in south-west Victoria. A step-by-step process was used, determining risk factors for various events preceding the first calving period and then utilising these outcomes as explanatory variables for subsequent lactation and reproductive performance in the first lactation. The pre-weaning events of 963 heifer calves on 9 dairy herds were recorded. Variables included: season of birth; presence of dystocia or twinning; dam breed and age; dam leaking colostrum prior to calving; time between birth and first/second feeds of colostrum; volume and quality of colostrum produced by the dam; volume of first and second feeds of colostrum; evidence of passive transfer of immunity; morbidity during the pre-weaning period; average daily gain during the pre-weaning, pre-pubertal and post-pubertal periods; and periparturient disease at the first calving. Aspects of the management of these animals were recorded in a detailed interview process prior to the commencement of the study. First lactation performance was determined from monthly herd testing data from which 100-day and 250-day milk yield, protein and fat production were estimated. Reproductive performance was measured using the interval between first mating start date to first insemination and the interval between first mating start date to conception in survival analysis models. The results identified important risk factors for colostrum quality, pre-weaning morbidity, passive transfer status, average daily gain and lactation and reproductive performance. Dams leaking milk prior to calving were twice as likely to have poor quality colostrum. Volume of first colostrum produced was closely associated with colostrum quality. The age of the dam and the breed of the heifer calf were correlated with passive transfer of immunity. Season of birth was identified as a risk factor for pre-weaning morbidity. Average daily gain from birth to first calving was associated with season of birth and breed of heifer. Pre-pubertal average daily gain had the largest influence on 100-day and 250-day performance. For each 0.1kg of pre-pubertal daily growth there was an increase in milk yield (182 litres), protein yield (4.0kg) and fat yield (4.1kg) during the first 100 days of lactation. Events early in life such as dystocia and season of birth had substantial effects on first lactation performance. Increasing post-pubertal average daily by 0.1kg/day, increased the daily likelihood of insemination and conception in the first mating period after calving by 10%. Heifers that suffered periparturient disease at their first calving were less likely to conceive in the first mating period post-calving. Good management of heifer calves to ensure optimal growth is associated with significant improvements in production and reproductive performance once they enter the herd