Metabolic investigations into dairy cow longevity

Dairy cow longevity is a determined by health, reproduction, production, management, and chance events. Optimising longevity can reduce replacement demands, enable beef diversification, lower lifetime emissions, improve feed efficiency, and enhance the industry’s social license. Although increasing parity is associated with increased health events, reproductive inefficiency, culling and mortality, the underlying metabolic changes are poorly defined. Identifying the physiological changes associated with parity may reveal opportunities to improve survival and optimise production. This thesis explored longevity across three themes: 1) body tissue reserves and their association with housing systems, parity and blood metabolites; 2) association between age, housing system, reproduction and health; and 3) lipidomic and metabolite associations with age, housing systems, and survival. Thirty farms (15 pasture, 15 confinement) contributed parity-stratified cows totalling approximately 1,700 samples. Targeted LC-MS quantified 185 plasma lipids, and colorimetric analysis 15 serum metabolites. Higher parity cows had greater body weight, but lower body condition score. Albumin was consistently associated with the tissue reserves. Increasing parity reduced reproductive efficiency and increased hazards of mastitis and lameness. Confinement systems had higher mastitis risk than pasture systems, but did not differ in reproductive or lameness risk. Glycerophospholipids containing omega-3 fatty acids were lower in older cattle and in confinement systems, and lower concentrations were associated with increased hazards of culling. These finding suggest age-related alteration in omega-3 pathways may contribute to adverse outcomes. This thesis represented the first application of lipidomics to ageing and survival in dairy cattle and identified omega-3 pathways as targets for feeding trials to improve longevity and sustainability.