Effect of estradiol preceding and progesterone subsequent to ovulation on proportion of postpartum beef cows pregnant

Authors: CIERNIA, LAUREN - University Of Missouri; PERRY, GEORGE - South Dakota State University; SMITH, MICAHEL - University Of Missouri; RICH, JERICA - South Dakota State University; NORTHROP, EMMALEE - South Dakota State University; PERKINS, STEPHANIE - South Dakota State University; GREEN, JONATHAN - University Of Missouri; Zezeski, Abby; Geary, Thomas

Submitted to: Animal Reproduction Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2021
Publication Date: 2/17/2021
Citation: Ciernia, L.A., Perry, G.A., Smith, M.F., Rich, J.J., Northrop, E.J., Perkins, S.D., Green, J.A., Zezeski, A.L., Geary, T.W. 2021. Effect of estradiol preceding and progesterone subsequent to ovulation on proportion of postpartum beef cows pregnant. Animal Reproduction Science. 227. Article 106723. https://doi.org/10.1016/j.anireprosci.2021.106723.
DOI: https://doi.org/10.1016/j.anireprosci.2021.106723

Interpretive Summary: In a previous study, preovulatory estradiol (E2) at induced ovulation and postovulatory progesterone (P4) were the two most important factors affecting pregnancy success in beef cows. Two studies were conducted to evaluate effects of E2 and P4 on pregnancy. In study 1, cows with greater E2 had greater pregnancy rates. The aim of study 2 was to differentiate between effects of high or low E2 and normal or low P4 on pregnancy rate. Half of the cows with high or low E2 were given prostaglandin (PGF) on day 3, 3.5 and 4 after estrus to create the low P4 groups. Only cows that did not express estrus were used in the study. All cows received an embryo on day 7. Level of P4 was reduced in cows that received PGF. Pregnancy rates for low E2/low P4, low E2/normal P4, high E2/low P4 and high E2/high P4 were 22%, 30%, 47%, and 58%. In summary, preovulatory E2 had a significant positive effect on pregnancy success and postovulatory P4 influenced pregnancy success in cows with low E2.

Technical Abstract: In a previous study, preovulatory estradiol (E2) on d 0 (gonadotropin releasing hormone [GnRH]-induced ovulation) and postovulatory progesterone (P4) on d 7 were the two most important factors affecting establishment of pregnancy in postpartum beef cows. Therefore, two experiments were conducted to further examine the effect of circulating concentrations of E2 at GnRH-induced ovulation (d 0) and the effect of decreasing circulating postovulatory P4 (prostaglandin F2a [PGF] injections on d 3, 3.5, and 4) on pregnancy rate in postpartum beef cows following embryo transfer. In experiment 1, ovulation was synchronized in postpartum cows (n = 777) as follows: on d -9 GnRH (GnRH1) and an intravaginal P4 implant (CIDR) were administered, on d -2 the CIDR was removed and PGF administered, and on d 0 GnRH (GnRH2) was administered. Estrous detection patches (Estrotect) were placed on cows on d -2, and any cow with an activated patch on d 0 was considered to have exhibited estrus and removed from the study (n = 424). For the remaining cows (n = 353), blood samples were collected on d -2 and 0, and plasma analyzed for E2 by radioimmunoassay. Recipient cows were classified, based on their d 0 concentration of E2 (mean ± SEM), into the following groups: Low (2.46 ± 0.07 pg/mla; n = 112), Medium (3.87 ± 0.07 pg/mlb; n = 134), and High (5.76 ± 0.07 pg/mlc; n = 107) E2 groups (abcP < 0.0001). Each cow received an in vivo produced embryo on d 7 and pregnancy diagnosis occurred between d 29 and 34 of gestation. Pregnancy rate for the Low, Medium, and High E2 cows was 36%a, 44%a, and 56%b (abP < 0.05). Furthermore, change in E2 from d -2 to 0 had a positive correlation with pregnancy rate (r = 0.13; P = 0.01). The objective of experiment 2 was to differentiate between independent effects of Low or High preovulatory E2 and Low or Normal postovulatory P4 on pregnancy rate following embryo transfer. Ovulation was synchronized in postpartum beef cows (n = 679) as described for experiment 1. Cows not detected in estrus between d -2 and d 0 were classified based on d 0 concentrations of E2 as either Low (mean ± SEM; 2.60 ± 0.07 pg/mla; n = 140) or High (5.76 ± 0.08 pg/mlb; n = 147; abP < 0.0001) and subsequently assigned to a Low (PGF injections on d 3, 3.5, and 4) or Normal (no treatment) P4 group. Final treatment groups were as follows: Low E2-Low P4 (LL; n = 71), Low E2-Normal P4 (LN; n = 69), High E2-Low P4 (HL; n = 74), and High E2-Normal P4 (HN; n = 73). Each cow received an in vivo produced embryo on d 7 and pregnancy diagnosis occurred on d 34. Concentrations of P4 on d 7 were decreased (P < 0.05) in HL compared to HN, and in LL compared to LN groups. Estradiol on d -2, 0, and change in E2 (d -2 to d 0) positively influenced pregnancy rates (P < 0.008), and pregnancy rates for LL, LN, HL, and HN were different (22%a, 30%a, 47%b, and 58%b; P < 0.02ab). Within E2 groups (Low E2 [LH +LL] and High E2 [HH+HL]), P4 on d 7 had a positive effect on probability of pregnancy in the Low E2 (P = 0.01), but not High (P = 0.92) E2 groups. In summary, preovulatory E2 had a significant positive effect on the establishment of pregnancy; whereas, postovulatory P4 had a positive effect on pregnancy when preovulatory E2 was Low in postpartum beef cows.