183 Relationship of steroid hormone dynamics prior to artificial insemination and pregnancy establishment following estrus detection or Double-Ovsynch in lactating dairy cows
T. Minela A , A. Santos A , J. Branen A and J. R. Pursley BA
B
The interaction of steroid hormones around ovulation plays important roles in uterine receptibility and early embryonic development. Our aim was to characterise steroid hormone dynamics around AI in cows receiving first service following oestrus detection (ES) or Double-Ovsynch (DO). We hypothesised that distinct 17β-oestradiol (E2) and progesterone (P4) interactions would be associated with pregnancy outcomes, utilising the first day of pregnancy specific protein B (PSPB) increase, or presumptive conceptus attachment (pCA) as the initial reference. Lactating dairy cows were blocked by parity and randomly assigned to AI following ES (n = 55) or DO (n = 54). Ovarian dynamics were assessed via ultrasonography. Blood samples were collected at the day of final GnRH (DO) or 2–12 h after oestrus onset (ES) for determination of E2 and P4 concentrations. A ratio between E2:P4 was calculated to describe dynamic changes of these hormones before AI. The E2:P4 ratio was divided across treatments into tertiles. Daily blood samples were collected between Day 17–28 post-ovulation for determination of PSPB concentrations. The day of pCA was calculated as ≥12.5% increase from a baseline (average of Day 17–18) followed by two more days of ≥12.5% increase from the previous day. Pregnancy was confirmed between 31–37, and 59–65 days post-AI with ultrasound. Models included the fixed effects of treatment and parity, and E2:P4 ratio tertile if applicable. Binary outcomes and continuous and repeated outcomes were analysed in SAS with PROC GLIMMIX and MIXED, respectively. Logistic regression was estimated on PROC LOGISTIC. Tertiles of the E2:P4 ratio described distinct scenarios of steroid hormone changes around AI (P < 0.01). The bottom tertile included cows with the highest P4 and lowest E2 concentrations, the mid tertile had intermediate E2 and P4 concentrations, and the top tertile included cows with the greatest E2 and lowest P4 concentrations. A key difference between treatments was the ovulation of smaller follicles in DO (P ≤ 0.02) compared with ES, regardless of tertile. The E2:P4 ratio was a predictor of pCA for DO treatment (P = 0.01), but not ES (P = 0.3). Overall, cows that maintained pregnancy had a greater E2:P4 ratio in comparison with nonpregnant cows (9.3 ± 0.81 vs 7.4 ± 1.1; P = 0.02). Cows that lost pregnancy did not differ in E2:P4 ratio (8.4 ± 1.6) in comparison with cows that maintained pregnancy and nonpregnant cows (P ≥ 0.35). At first pregnancy diagnosis (Days 31–37), DO cows within the top tertile had greater pregnancies/AI (85.7%) in comparison with ES cows assigned to both the bottom (31.6%) and top tertile (33.3%; P = 0.05). Steroid hormone interactions around AI were associated with percentge of DO cows with pCA, but not with pregnancy maintenance in either treatment. Exogenous control of follicular development resulted in ovulation of smaller follicles in DO-treated cows, which when secreting the higher E2 under the lowest P4 concentrations resulted in greater pCA.
