Temporarily decreasing progesterone after timed artificial insemination decreased expression of ISG15 in blood leukocytes, serum PSPB concentrations, and embryo size in lactating Holstein cows

Abstract Text: Our objective was to evaluate the effect of temporarily decreasing progesterone (P4) after timed artificial insemination (TAI) in dairy cows. Lactating Holstein cows (n = 80) were synchronized for first TAI using a Double-Ovsynch protocol, and were randomly assigned to receive 12.5 mg PGF_2α (dinoprost tromethamine) 5 d after the last GnRH treatment (LowP4) or serve as untreated controls (HighP4). Blood samples were collected thrice weekly from 5 to 32 d after TAI for all cows and from 32 to 67 d for pregnant cows, and were analyzed for P4 and PSPB concentrations. Expression of interferon-tau stimulated gene 15 (ISG15) was assessed in blood leukocytes 18 and 20 d after TAI. Pregnancy diagnosis was performed weekly using ultrasound from 32 to 67 d after TAI, and embryo size (crown-rump length) was measured 32, 39, and 46 d after TAI. Data were analyzed by ANOVA and logistic regression using the MIXED and GLIMMIX procedures of SAS. LowP4 cows had less (P < 0.01) P4 than HighP4 cows from 6 to 11 d after TAI, however, pregnancy outcomes 32 d after TAI [43% (17/40) for both treatments, P = 0.97] and pregnancy loss from 32 to 67 d after TAI [6% (1/17) vs. 6% (1/17) for LowP4 and HighP4, P = 0.84] did not differ between treatments. HighP4 cows diagnosed pregnant 32 d after TAI had greater (P < 0.05) expression of ISG15 20 d after TAI than LowP4 cows diagnosed pregnant 32 d after TAI (7.7 vs. 4.9 fold increase from d 4). Pregnant HighP4 cows had greater (P < 0.01) PSPB concentrations from 25 to 67 d after TAI than pregnant LowP4 cows. Embryo crown-rump length did not differ between treatments 32 and 39 d after TAI, but HighP4 cows had larger (P < 0.05) embryos 46 d after TAI (26.0 ± 1.0 vs. 23.5 ± 1.0 mm). We conclude that treatment with 12.5 mg of PGF_2α 5 d after induction of ovulation temporarily decreased P4 concentrations from 6 to 11 d after TAI without inducing luteal regression. Decreasing P4 after TAI decreased expression of ISG15 in blood leukocytes 20 d after TAI, serum PSPB concentrations 25 to 67 d after TAI, and embryo size 46 d after TAI but did not affect P/AI in lactating Holstein cows. Supported by USDA NIFA Hatch project 1006519

Keywords:  embryo; ISG15; progesterone; PSPB;