Influence of Days in Milk and Parity on Milk and Blood Fatty Acid Concentrations, Blood Metabolites and Hormones in Early Lactation Holstein Cows

SIMPLE SUMMARY: At the onset of lactation, the energy intake is not sufficient to meet the high energy requirement due to milk production increase. Consequently, body reserve is mobilized to support this negative energy balance situation. Severe negative energy balance can lead to health and production concerns. Certain blood and milk parameters could be used as indicators of lipomobilization and can thus predict the energy status in postpartum cows. Therefore, the objective of this paper was to study the influence of physiological factors that affect the energy balance, such as lactation stage and parity, on blood and milk parameters in healthy early lactation cows. Thirty-two Holstein dairy cows from five Belgian commercial farms were followed during two calving periods. This study confirms that lactation stage along with energy balance and parity significantly influence blood and milk parameters. ABSTRACT: The objective of this paper is to study the influence of physiological factors that affect the energy balance, such as lactation stage and parity, on milk yield and composition, milk and blood fatty acid concentrations, blood metabolites and hormones in healthy early lactation cows. Thirty-two Holstein dairy cows from five Belgian commercial farms were followed. The grass silage-based diets fed to cows fell within normal composition ranges typically offered to dairy cows on commercial dairy farms in the region. Milk and blood were sampled at each official milk recording and used for the determination of milk fat and protein, milk and blood fatty acids, blood metabolites and hormones concentrations. The considered period was 7 to 150 days in milk. As lactation progressed, concentrations of milk 18:0 and 18:1c9, as well as blood non-esterified fatty acids and β-hydroxybutyrate, decreased, and those of milk C4–C14, blood cholesterol, triglycerides, insulin and IGF-I increased, agreeing with the extensive mobilization of body reserves in early lactation. Lower concentrations of milk C4–C14 and 16:0 and concomitant higher concentrations of milk 18:0 and 18:1c9 suggest a larger body reserve mobilization in first parity cows compared with greater than or equal to second parity cows. This study confirms that early lactation stage along with parity significantly influence milk fatty acids, such as 18:1, and blood metabolites and hormones, such as NEFA and insulin.