Effect of energy density in the diet and milking frequency on plasma metabolites and hormones in early lactation dairy cows.

The effects of energy density in the diet [low = 0.86 SFU/kg dry matter (DM) or high = 1.06 SFU/kg DM] and daily milking frequency (two or three times) in early lactation on plasma concentrations of metabolites and hormones were evaluated in 40 Holstein dairy cows arranged in a 2 x 2 factorial block design. The four treatment combinations were L2, L3, H2 and H3, and the experimental period comprised the first 8 weeks of lactation. Plasma glucose, insulin and insulin-like growth factor (IGF)-I concentrations were on average 8 (3.43 versus 3.19 mmol/l), 114 (41.6 versus 19.4 pmol/l) and 60% (91.9 versus 57.4 ng/ml) higher, whereas beta-hydroxybutyrate (BOHB), plasma urea nitrogen (PUN) and growth hormone (GH) concentrations were on average 18 (0.73 versus 0.89 mmol/l), 14 (7.18 versus 8.35 mmol/l), and 63% (1.0 versus 2.6 ng/ml) lower for cows fed diet H than for cows fed diet L. Cows milked three times daily had a 6% (3.20 versus 3.42 mmol/l) lower plasma glucose concentration and a 19% (0.88 versus 0.74 mmol/l) higher plasma concentration of BOHB compared with cows milked two times daily. Plasma non-esterified fatty acid (NEFA) concentration was not affected by either treatment. Overall, it is concluded that increasing the daily milking frequency creates a higher metabolic imbalance in early lactation. Cows in early lactation will benefit from receiving a high energy density diet and thereby avoid a too high metabolic imbalance when mobilizing body tissue in support of milk production.