Long-term oral drenching of crude glycerol to primiparous dairy cows in early lactation

The objective of this experiment was to study the long-term effects of supplemental oral drenching of crude glycerol (CG) on feed intake, milk yield and composition, plasma metabolites and energy balance indices of primiparous dairy cows in early lactation. Fourteen primiparous Holstein dairy cows were paired according to body weight (BW) and body condition score (BCS) at calving, and allocated at random to either a treatment or a control group. Both groups were fed a basal diet, containing 11.4 MJ kg−1 DM metabolisable energy and 103 g/kg DM metabolisable protein, twice a day. Silage (ad libitum) and a pelleted concentrate mixture with mineral mix were fed separately during the three six-day periods from days 4 to 21 post partum. An oral drench of 500 ml of CG mixed with lukewarm water was fed supplementally before the morning feedings to the treatment groups, while the control group were given no oral drench. Blood samples were collected on two consecutive days at the end of each six-day period before administration of glycerol. Results showed that long-term administration of CG increased silage intake (P<0.001), and total dry matter intakes (DMI; P=0.023). Oral drenching with glycerol increased milk yields (P<0.01), and milk lactose content (P<0.001). Supplemental glycerol had no effect on estimates for milk energy, milk constituent ratios or milk acetone content. No differences in BCS changes or on concentrations of plasma glucose, insulin, and β-hydroxybutyrate (BHB) were found between the two groups. Dairy cows given oral glycerol had lower concentrations of plasma urea (P=0.005) during the post partum period. There was a treatment and time interaction effect on the non-esterified fatty acids (NEFA) concentration (P=0.048), although this was complex, and the only period of significant differences was in the first six-day period, when NEFA concentration was higher (P=0.025) in the control group. The data indicate that prolonged oral drenching of supplemental CG in the early lactation period improves total DMI, and therefore has a positive effect on milk yield of primiparous dairy cows in this period.