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Factors associated with average daily gain in dairy heifer calves on U.S. dairy operations
The objective of this study was to evaluate average daily gain (ADG) in U.S. dairy heifer calves based on different health, feeding, and management practices, as well as environmental factors. This study was conducted as part of the calf component of the National Animal Health Monitoring System’s Dairy 2014 study, which included 104 dairy operations in 13 states. The calf component was an 18-mo longitudinal study focused on dairy heifer calves from birth to weaning. This analysis included data from 1,331 Holstein calves. The mean ADG was 0.75 kg/day (SE = 0.007), and calves were fed liquid diets an average of 63.8 days (SE = 0.4). Backward elimination model selection in Proc Mixed of SAS® was used after univariate screening (P < 0.2) to determine which environmental factors, diet, and management practices significantly impacted ADG. The final model included disease Y/N (P < 0.001), kg protein fed in the liquid diet per day (P < 0.001), the average temperature and humidity index for the preweaning period (P < 0.001), dam lactation number (P < 0.001), bedding type (P < 0.001), and singleton vs. twin birth (P = 0.006). After controlling for other independent variables in the model, calves with no disease events gained on average 0.05 kg/day more than calves with one or more disease events. Every 1 kg of protein fed per day equated to 0.1 kg/day of gain. Each 10-unit decrease in THI equated to 0.02 kg/day of gain. Calves from third or higher lactation dams had the highest gains (0.68 kg/day), followed by second lactation dams, and last first lactation dams (0.63 kg/day). Calves bedded with a combination of bedding materials gained the most (0.72 kg/day), followed by those bedded with shavings, then straw or hay, and lastly no bedding or sand (0.52 kg/day). Single calves gained 0.08 kg/day more than twins. These results highlight the importance of feeding an appropriate quantity and quality of a liquid diet, keeping calves healthy, and mitigating the effects of temperature and humidity on ADG.
Keywords: dairy heifers; average daily gain; calf nutrition