Prostaglandin F2a Concentrations, Fatty Acid Profiles, and Fertility in Lipid-Infused Postpartum Beef Heifers1

Effects of lipid infusion into postpartum (PP) beef heifers on plasma concentrations of linoleic acid and prostaglandin (PG) F2a metabolite (PGFM), days to first estrus, and subsequent pregnancy rate were examined. Treatments (n 5 5 per group) of 1 L intralipid (20% soybean oil; IL), 1 L 50% dextrose (DEXT; isocaloric to IL), 0.5 L intralipid (0.5 IL), and 1 L physiological saline (SAL) were infused i.v. over 4 h on each of Days 7 through 11 PP. Capacity of the uterus to produce PG was evaluated after i.v. injection of 150 IU of oxytocin (OT) to ILand DEXT-treated heifers Day 12 PP. Change in plasma concentrations of PGFM from 0 to 4 h was greater for IL-treated heifers than for heifers given other treatments on Day 7 (P 5 0.04) and on Day 11 (P 5 0.01), but not on Day 9 (P . 0.10). Plasma linoleic acid on Day 11 and OT-induced release of PGFM on Day 12 were greater in IL-treated heifers compared with DEXT-treated heifers (P , 0.06 and P 5 0.01, respectively). There were no significant differences among treatments for mean days to first estrus or pregnancy rate. Infusion of lipid increased systemic concentrations of linoleic acid and increased the capacity of PP heifers to produce uterine PGF2a as indicated by plasma PGFM concentration after OT injection.