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 heife rs, averaging 90 d prior to calving at initiation of the trial, were i n a 4 x 4 Latin square design with 12-d periods. Heifers consumed alfa lfa silage on an ad libitum basis during d 1 to 7 of each period. Duri ng d 8 to 12, heifers were gradually restricted to 50% of ad libitum i ntake. Heifers received an oral drench of O, 296, 592, or 887 mi of pr opylene glycol once daily at 6 h prior to feeding on d 8 to 12. Propyl ene glycol linearly increased glucose and insulin and decreased BHBA a nd NEFA in blood. Quadratic effects of propylene glycol on plasma gluc ose, BHBA, and NEFA also occurred; response per milliliter of propylen e glycol was greatest at the lowest dose. The highest dose of propylen e glycol returned blood glucose, insulin, and NEFA concentrations to t hose prior to feed restriction. Ruminal acetate to propionate ratio de creased as propylene glycol dose was increased, indicating ruminal con version of propylene glycol to propionate. A dose of 296 ml of propyle ne glycol was almost as effective as a dose of 887 ml in reducing lipi d mobilization during restricted feed intake.