Metabolism of dairy cows as affected by dietary starch level and supplementation with monensin during early lactation

Abstract Text: The objective of this study was to evaluate the impact of dietary starch level and monensin (M) on metabolism of dairy cows during early lactation. Primiparous (n=21) and multiparous (n=49) Holstein cows were fed high starch (HS; 26.2% starch, 34.3% NDF, 22.7% ADF, 15.5% CP) or low starch (LS; 21.5% starch, 36.9% NDF, 25.2% ADF, 15.4% CP) TMR beginning at parturition until 21 DIM with a topdress pellet containing 0 or 450 mg/d M in a completely randomized design with a 2 × 2 factorial arrangement of treatments. Prior to parturition all cows were fed a common controlled energy diet with daily topdress of either 0 or 400 mg/d M consistent with postpartum treatment. Postpartum blood samples were collected 3× per wk and liver biopsies were taken on d 7 ± 4. Cows fed HS had higher plasma glucose (57.5 vs. 53.9 mg/dL; P = 0.003) and insulin (0.26 vs. 0.19 ng/mL; P = 0.008), and lower NEFA (533.1 vs. 696.6 µEq/L; P = 0.002) than cows fed LS. Cows fed LS had elevated BHBA during 11 to 21 DIM compared to cows fed HS (starch × d; P = 0.04). There was no effect of M on postpartum plasma NEFA. Cows fed M had higher plasma glucose compared to controls (58.1 vs. 53.3 mg/dL; P < 0.001) which was driven by a M × parity interaction in which heifers fed M had greater plasma glucose concentrations than controls (62.0 vs. 54.2 mg/dL; P=0.008). Cows fed M had lower plasma BHBA compared to controls (10.08 vs. 12.66 mg/dL) which was contributed to by a M × parity interaction in which heifers fed M had lower BHBA concentrations than controls (10.11 vs. 13.99 mg/dL; P = 0.03). There was no effect of starch treatment on overall liver triglyceride content. Heifers fed M had increased liver triglyceride content compared to control heifers and cows fed M had decreased liver triglyceride content compared to control cows (M × parity; P = 0.05). Cows fed LS with M had higher liver glycogen content than cows fed the LS without M, with no effect of M treatment for cows fed HS (starch × M; P= 0.008). Overall, animals fed HS postpartum and M throughout the transition period exhibited improvements in energy metabolism during early lactation.

Keywords: Starch, monensin, metabolism