Feeding glycerol to transition dairy cows: effects on blood metabolites and lactation performance

Glycerol can alleviate the symptoms of ketosis when delivered as an oral drench. The addition of glycerol to the diet would eliminate the need for restraining cows for drenching yet deliver a glucogenic substrate, alleviate the fatty liver-ketosis complex, and improve lactational performance. For this study, 21 multiparous and 9 primiparous Holstein cows blocked by parity and expected calving date were used in a randomized block design to evaluate the effects of feeding glycerol from 14 d prepartum to 21 d in milk (DIM). Treatments (kg/d dry matter basis) were 0.86 of cornstarch (control), 0.43 cornstarch + 0.43 glycerol (LG), or 0.86 glycerol (HG), topdressed and hand-mixed into the upper one-third of the daily ration. All cows were fed a common diet from 22 to 70 DIM. Prepartum dry matter intake (DMI) was greater for cows fed the control diet compared with LG or HG (13.3, 10.8, and 11.3 +/- 0.50 kg/d, respectively). Prepartum plasma glucose, insulin, beta-hydroxybutyrate, nonesterified fatty acids, and ruminal profiles were not affected by treatments. Rumen fluid collected postpartum from cows fed LG and HG had greater total volatile fatty acids, greater molar proportions of propionate, and a decreased ratio of acetate to propionate. Furthermore, concentrations of butyrate tended to be greater in rumens of cows fed LG and HG. Postpartum concentrations of glucose in plasma were greatest for cows fed the control diet relative to LG and HG (66.0 vs. 63.1 and 58.4 mg/dL, respectively) and decreased sharply at 21 DIM, after treatments ended, for cows fed HG (diet x day interaction). Body weight and condition loss, plasma nonesterified fatty acids, and liver lipids during the first 21 DIM were similar among treatments. Postpartum DMI was not affected by treatments; however, a tendency was observed for a diet x day interaction for body weight, as cows fed LG gained more body weight from 21 to 70 DIM relative to cows fed HG. Yield of energy-corrected milk during the first 70 DIM tended to be greatest for cows fed the control diet. The LG and HG diets decreased urea nitrogen concentrations in milk relative to controls. Based upon prepartum DMI and concentrations of glucose and beta-hydroxybutyrate in blood postpartum, feeding glycerol to dairy cows at the levels used in this experiment increased indicators used to gauge the degree of ketosis in dairy cattle.