89 Effects of oestradiol on PGF2α release and corpus luteum function during early pregnancy in beef heifers
I. G. Motta A , T. K. Nishimura A , D. A. S. Poit A , K. G. Morelli A , A. L. Neto A , G. A. Bruni A , P. A. Ferraz A , A. Guimarães da Silva A , T. Castro B , O. J. Ginther B and G. Pugliesi AA Department of Animal Reproduction, School of Veterinary Science and Animal Science, University of São Paulo, Pirassununga, SP, Brazil
B University of Wisconsin-Madison, Madison, WI, USA
Reproduction, Fertility and Development 35(2) 170-171 https://doi.org/10.1071/RDv35n2Ab89
Published: 5 December 2022
© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the IETS
We aimed to evaluate the effects of different oestradiol (E2) benzoate (EB) doses at 13 days after ovulation on PGF2α release and corpus luteum size and function in pregnant and nonpregnant beef heifers. A total of 69 cycles of 47 Nelore heifers aged 18–24 months old, with average bodyweight of 390 ± 35 kg were used. Oestrus was synchronised with two i.m administrations of 0.53 mg of sodium cloprostenol (Sincrocio, Ourofino Saúde Animal) 12 days apart. Heifers who exhibited oestrus were randomly subdivided into non-inseminated (n = 19) or inseminated (n = 50) groups. Daily ultrasonography exams were performed to determine the day of ovulation (D0). On D13, heifers were randomly assigned to three experimental groups to receive 0, 1, or 2 mg of EB (Sincrodiol, Ourofino Saúde Animal) (non-inseminated: EB-0 [n = 6]; EB-1 [n = 7]; EB-2 [n = 6] and inseminated: EB-0 [n = 10]; EB-1 [n = 16]; EB-2 [n = 24]). On D13, blood samples were collected at hour 0 (H0), which was before the treatment, and thereafter hourly from H3 to H12 to measure plasma concentrations of PGF2α metabolite (PGFM). Doppler ultrasonography was performed daily from D13 to D19. Pregnancy check was done on D28. Data were analysed as a 2 × 3 factorial design (factor 1: pregnant vs non-inseminated; and factor 2: EB dose) by ANOVA or Fisher’s exact test in SAS. The proportion of pregnant heifers was greater (P < 0.05) in the EB-0 group (90%) than in the EB-1 (50%) and EB-2 (29%) groups. Plasma E2 was evaluated at hours 5, 6, 11, and 12 in pregnant heifers, and was greater (P < 0.0001) in EB-2 than in EB-1, which was greater than EB-0. The average PGFM concentrations over H3 to 12 was greater (P < 0.002) in EB-1 and EB-2 groups, regardless of pregnancy status. A significant interaction of pregnancy status by time (P = 0.06) indicated that PGFM concentrations reached a peak at hour 6 in non-inseminated, and at hour 8 in pregnant heifers. The day of structural luteolysis was earlier (P = 0.04) in the combined EB-1 and EB-2 groups (16.31 ± 0.17 days) than in the EB-0 group (17.29 ± 0.60 days). For CL area, a significant interaction between time and pregnancy status was observed. In non-inseminated heifers, CL area decreased progressively from D14 until D18, whereas in pregnant heifers, CL area did not differ between D13 to D19. A significant interaction between treatment group and time indicated that CL area did not change over time in the EB-0 group, whereas in EB-1 and EB-2 groups, a progressive decrease occurred from D14 and D15, respectively. For CL blood perfusion, there was a significant interaction (P = 0.03) among treatment group, time, and pregnancy status. In non-inseminated heifers, CL blood perfusion decreased more slowly in the EB-0 group than EB-1 and EB-2 groups. In pregnant heifers, no drop in CL blood perfusion was observed in any group. In conclusion, administration of 1 or 2 mg EB at 13 days after ovulation induces PGF2α release regardless of pregnancy status, anticipates luteolysis, and reduces pregnancy success in Nelore heifers.
This research was supported by São Paulo Research Foundation (FAPESP, grant# 2017/18937-0)/National Council for Scientific and Technological Development (CNPq).
