Development And Evaluation Of Feed Intake And Energy Balance Prediction Models For Lactating Dairy Cattle PDF Download

Feed is the single greatest expense on a dairy farm, representing approximately half the cost of dairy production over the last ten years. Increasing feed efficiency can reduce feed costs while maintaining milk production levels, improving profitability and sustainability of dairy production. Residual feed intake (RFI) is a measure of feed efficiency that represents the unexplained variation in feed intake after accounting for known energy sinks (i.e., milk energy output, body size, body weight change) within a group of cows managed similarly. Dry matter intake (DMI) is required to determine RFI, yet it is labor intensive and cost prohibitive to collect on most privately-owned dairies. Accurate prediction models of DMI could replace physical measurement, allowing for phenotypic feed efficiency determination on privately-owned dairies. When comparing multiple predictive approaches, traditional linear regression approaches performed as well as, or better than, more advanced techniques. Incorporation of behavioral sensor variables, but not blood metabolites, improved models of DMI, representing an opportunity to improve current models of DMI. Deeper understanding of the mechanisms that contribute to variation in feed efficiency would provide further insight into genetic selection for feed efficiency and can lead to the development of management and nutrition strategies to improve feed efficiency. Postpartum health may influence RFI, given the relationship with energy balance; however, no relationship exists between postpartum health disorders and same-lactation RFI, indicating that genetically selecting for RFI will not inadvertently select for negative health outcomes. Post-absorptive nutrient metabolism was previously identified in beef cattle as a source of variation in RFI, but was not investigated in lactating dairy cows. Between cows divergent in RFI, the blood circulating profile of metabolites differed, indicating differences in fatty acid or amino acid oxidation and providing evidence that post-absorptive nutrient metabolism is a source of variation in RFI of dairy cows. Differences in liver tissue pathways related to oxidative stress, cell cycling, and immune function, and differences in muscle fatty acid and glucose metabolism were identified, suggesting tissue-specific differences that contribute to variation in RFI. This dissertation details deeper understanding of post-absorptive nutrient metabolism as a source of variation in RFI, and ongoing effort will contribute to improving the feed efficiency of the dairy breed, which could have measurable impacts profitability and sustainability of dairy production.