HEMATOLOGICAL PROFILES ASSOCIATED WITH PRODUCTIVE PERFORMANCE AND ESTRUS STATE IN GRASS-FED BEEF HEIFERS
Feeding expenses and reproductive success are major drivers impacting profitability in the cow-calf sector. Similarities between feed efficient phenotypes and estrus state may be supported by markers of energetic shifts. Hematological measures associated with energy metabolism were investigated as proxies of feed efficiency and estrus in forage-fed beef heifers. Experiment 1 evaluated blood cell parameters, immunoglobulins and metabolites in relation to feed efficiency and heifer physiological state; Experiment 2 assessed metabolites to serve as proxies for estrus. Efficient heifers had greater lymphocytes, immunoglobulin M response, and lower alkaline phosphatase (ALP) concentrations. Efficient pregnant heifers had lower concentrations of cholesterol and globulin. Estrus state was strongly associated with fluctuations of ALP, aspartate aminotransferase, beta-hydroxybutyric acid, creatine kinase and triiodothyronine concentrations. However, age, body size and composition may influence such associations. There is potential for hematological parameters to serve as proxies of metabolic shifts related to feed efficiency and estrus state.