Effect of propylene glycol dosage during feed restriction on metabolites in blood of prepartum Holstein heifers.

Different doses of propylene glycol were compared for lowering plasma NEFA concentration during restricted feed intake. Eight Holstein heifers, averaging 90 d prior to calving at initiation of the trial, were in a 4 x 4 Latin square design with 12-d periods. Heifers consumed alfalfa silage on an ad libitum basis during d 1 to 7 of each period. During d 8 to 12, heifers were gradually restricted to 50% of ad libitum intake. Heifers received an oral drench of 0, 296, 592, or 887 ml of propylene glycol once daily at 6 h prior to feeding on d 8 to 12. Propylene glycol linearly increased glucose and insulin and decreased BHBA and NEFA in blood. Quadratic effects of propylene glycol on plasma glucose, BHBA, and NEFA also occurred; response per milliliter of propylene glycol was greatest at the lowest dose. The highest dose of propylene glycol returned blood glucose, insulin, and NEFA concentrations to those prior to feed restriction. Ruminal acetate to propionate ratio decreased as propylene glycol dose was increased, indicating ruminal conversion of propylene glycol to propionate. A dose of 296 ml of propylene glycol was almost as effective as a dose of 887 ml in reducing lipid mobilization during restricted feed intake.