Effects of Method of Delivery of Glycerol on Performance and Metabolism of Dairy Cows During the Transition Period
ABSTRACT Holstein cows (n=48) entering second or greater lactation were utilized to determine the effects of method of delivery of glycerol on performance and metabolism of dairy cows during the transition period. Beginning 21 d before expected parturition, cows were fed either a control diet or a diet containing glycerol (5% of DM). After parturition, cows were assigned to one of four treatments in a 2 (dietary glycerol; 3.3% of DM) X 2 (glycerol drench; 500 ml/d for 5 d beginning at parturition) factorial arrangement. From d 22 through 63 of lactation, cows were fed the same diet. Feeding glycerol during the prepartum period increased prepartum DMI, but feeding glycerol during the postpartum period tended to decrease postpartum DMI and drenching glycerol for the first 5 d of lactation decreased postpartum DMI. Milk yield was not affected by feeding glycerol during either the prepartum or postpartum periods or drenching glycerol during the first 5 d of lactation. Percentages and yields of milk fat and true protein were not affected by feeding glycerol during either the prepartum or postpartum periods; however, drenching glycerol tended to decrease milk protein content and decreased milk lactose content. Glycerol fed during the prepartum period resulted in no significant effects on plasma glucose, NEFA or BHBA concentrations during the prepartum period with no carry over effects on postpartum metabolites. Prepartum incorporation of glycerol in the diet resulted in no significant effects in liver triglycerides or glycogen content in liver samples collected d 1 after calving compared with control cows with no carry over effects on postpartum liver triglycerides or glycogen content. Postpartum incorporation of glycerol in the diet resulted in no significant effects on postpartum liver composition. Short term (5-d) oral drenching of glycerol beginning at calving resulted in no significant effects on liver composition (d 10 and 21 postpartum) or on plasma glucose and NEFA. However, there was a trend for an increase in BHBA concentrations for cows drenched with glycerol. Intensive blood sampling performed on d 5 post calving demonstrated that a 500 ml oral bolus of crude glycerine significantly decreased plasma NEFA concentration with no overall significant effects on plasma glucose, BHBA, or insulin. Overall, incorporation of glycerol in to the diets of transition cows or the short-term oral drench of glycerol at calving resulted in few positive performance responses and only modest effects on metabolic variables studied.
Thomas Overton Michael Van Amburgh Ynte Schukken
Transiton cow; hepatic lipidosis
dissertation or thesis