Effect of Manipulating Progesterone before Timed Artificial Insemination on Reproductive and Endocrine Parameters in High Producing Dairy Cows

Our objective was to evaluate the effect of manipulating progesterone (P4) concentrations before timed artificial insemination (TAI) in high-producing dairy cows. Lactating Holstein cows (n=80) were synchronized for first TAI using a Double-Ovsynch protocol, and were randomly assigned to receive 25 mg PGF_2α (dinoprost tromethamine) 1 d after the first GnRH treatment of the breeding Ovsynch protocol that included a used CIDR insert (LowP4) or to receive 2 new CIDR inserts during the breeding Ovsynch protocol (HighP4). Ovulatory response at the end of the protocol was monitored by ultrasound evaluation of the ovaries. Blood samples were collected thrice weekly from -10 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. Data were analyzed by ANOVA and logistic regression using the MIXED and GLIMMIX procedures of SAS. From -10 to -1 d relative to TAI, P4 concentrations were greater (P<0.01) for HighP4 vs LowP4 (4.7vs1.7±0.3 ng/ml). Incidence of double ovulation was greater (P<0.01) for LowP4 than HighP4 cows (33% vs. 10%). Pregnancies per AI at 32 d after TAI did not differ (P=0.25) between LowP4 vs. HighP4 cows (52.5% vs. 45.0%), and pregnancy loss from 32 to 67 d after TAI did not differ (P=0.91) between LowP4 vs. HighP4 cows (24% vs. 22.0%); however, LowP4 cows had more twin pregnancies than HighP4 cows (29% vs. 0%). Diameter of the ovulatory follicles was greater (P=0.05) for LowP4 than HighP4 cows (15.9 vs. 14.6 mm). After TAI, LowP4 cows had greater (P=0.04) P4 concentrations than HighP4 cows (4.6vs.3.6 ng/mL) and pregnant cows had greater (P<0.01) P4 concentrations than open cows (5.2vs.2.8 ng/mL). PSPB concentrations tended to be greater (P=0.07) for LowP4 cows than HighP4 cows (1.1 vs 0.9). In addition, relative expression of ISG15 18 and 20 d after TAI was greater for LowP4 than HighP4 cows (D18: P=0.02, 2.5vs.4.5; and D20: P=0.05 6.3 vs. 3.9), and for pregnant than for open cows (D18: P<0.01, 4.9 vs. 2.2; and D20: P<0.01, 8.0 vs. 2.2). In conclusion, low P4 concentrations before TAI increased incidence of double ovulation at AI, twin pregnancies, PSPB concentration, and relative expression of ISG15 at 18 and 20 d after TAI