Effects of Monensin and Stage of Lactation on Variation of Blood Metabolites Within Twenty-Four Hours in Dairy Cows

Abstract

Effects of prepartum administration of a monensin controlled release capsule (CRC) and stage of lactation on variation of blood metabolites within 24h were determined in 16 dairy cows. Cows were fed a total mixed ration ad libitum twice daily at 0700 and 1300h. At calving, cows were switched from a close-up dry cow diet to a lactating cow diet. Cows were blood sampled every 3h for 24h at 3 stages of lactation, including 1 wk before calving (wk −1), 1 wk after calving (wk 1), and 6 wk after calving (wk 6). Serum concentrations of glucose, β-hydroxybutyrate (BHBA), nonesterified fatty acids (NEFA), and urea exhibited significant variation within 24h. Glucose and NEFA were, respectively, 0.09 and 0.08mM lower between 1030 and 2230h than between 2230 and 1030h. β-Hydroxybutyrate and urea were, respectively, 95.1 and 0.49mM higher between 1030 and 2230h than between 2230 and 1030h. Monensin did not significantly affect glucose, NEFA, and urea in this study. Monensin reduced BHBA at wk 1, but not at wk −1 or wk 6. Glucose was lower and BHBA and NEFA were higher at wk 1 compared with wk −1 and wk 6. Urea was higher at wk 6 compared with wk −1. The variation within 24h of glucose, BHBA, and NEFA were not affected by monensin and stage of lactation. Diurnal variation of urea was affected by stage of lactation, but not by monensin.