PSII-28 - Effect of route of administration of dinoprost tromethamine on serum profiles of PGFM and progesterone in lactating Holstein cows

Our objective was to compare serum profiles of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) and circulating progesterone (P4) concentrations in lactating Holstein cows based on route of administration of dinoprost tromethamine administered 7 d after administration of GnRH. Multiparous lactating Holstein cows were fitted with indwelling jugular catheters 6 d after the last GnRH treatment of an Ovsynch protocol (d 0), and cows were randomized on d 7 to receive 25 mg dinoprost tromethamine (2 mL Lutalyse® HighCon; Zoetis, Parsippany-Troy Hills, NJ) either s.c. in the neck (SC; n = 6) or i.m. in the semitendenous muscle (IM; n = 6). Blood samples were collected via jugular catheters 24, 2, and 1 h before treatment to establish baseline P4 concentrations. Blood samples were collected every 15 min after treatment for 1.75 h, then every 30 min for 48 h, and at 60 and 72 h with the last time point corresponding to timed AI after an Ovsynch protocol. Serum samples were stored frozen and later assayed for PGFM and P4 concentrations via ELISA. Circulating PGFM concentrations were greater (P < 0.05) for SC than for IM cows from 15 to 90 minutes after treatment which resulted in a greater (P = 0.02) area under the PGFM curve during the first 2 h after treatment (2,223 ± 160 pg•hr/mL vs. 1,586 ± 150 pg•hr/mL for SC vs. IM cows, respectively). By contrast, circulating P4 concentrations normalized to percent of baseline P4 concentrations did not differ between treatments at any time point after treatment during the experiment. In conclusion, although SC cows had greater circulating PGFM concentrations 15 to 90 min after treatment than IM cows, the decrease in circulating P4 concentrations during induced luteolysis did not differ based on route of dinoprost tromethamine administration. Supported by NIFA USDA Hatch project 1019532.