Hormonal therapeutic strategy on the induction of accessory corpora lutea in relation to follicle size and on the increase of progesterone in sheep

SOTO, A.T.; LACAU, I.M.; BRUNO- GALARRAGA, M.M.; CUETO, M.I.; FERNANDEZ, J.; DE LA SOTA, R.L.; GIBBONS, A.E.; SOTO, A.T.; LACAU, I.M.; BRUNO- GALARRAGA, M.M.; CUETO, M.I.; FERNANDEZ, J.; DE LA SOTA, R.L.; GIBBONS, A.E.

THERIOGENOLOGY

ELSEVIER SCIENCE INC

Año: 2018 vol. 105 p. 184 - 188

0093-691X

We determined the effect of GnRH or hCG treatment on day 4 post-time artificial insemination (FTAI) onthe formation of accessory corpora lutea (acc-CL) and on the concentration of serum progesterone (P4) insheep. Multiparous adult Merino ewes (n ¼ 36) were synchronized for estrus using double injection ofPGF2a agonist (125 mg Cloprostenol) with an interval of 14 days. At 53e56 h after the second PGapplication, FTAI was performed. On day 4 post FTAI, ewes were either treated with analogue of GnRH(4 mg buserelin; n ¼ 12) or hCG (300 IU, hCG; n ¼ 12) or saline solution (1 ml; Control; n ¼ 12). Twolaparoscopic ovarian examinations were performed on days 4 and 10 post FTAI. In the first observation,we determined the number of post ovulation corpora lutea (po-CL) and the site, number and diameter offollicles present in both ovaries. In the second laparoscopy, we observed the number of po-CL and acc-CL.The sizes of the follicles that generated the acc-CL were determined according to the position of thefollicles observed in the first laparoscopy. Serum P4 concentration was determined on days 4, 7, 10, 13, 17and 21 post FTAI by chemiluminescence. A similar follicular population in size and number was observedin the three experimental groups prior to the beginning of treatments (Follicles 2 mm: 6.4 ± 3.7, 3 mm:3.0 ± 2.3, 4 mm: 1.1 ± 0.5, 5 mm: 1.4 ± 0.8; P ˃ 0.05). The formation of 1.0 ± 0.4 and 1.1 ± 0.3 acc-CL wasobserved in the GnRH and hCG groups, respectively (P ˃ 0.05), but was not observed in the Control group(P < 0.05). Follicle sizes from which acc-CL generated were 3, 4 and 5 mm and did not differ betweenhormonal treatments (P ˃ 0.05). The hCG group had higher mean concentrations of P4 on days 7, 10, 13and 17 post FTAI compared with the GnRH group and the Control group (P < 0.05), while no differenceswere observed between these two latter groups (P > 0.05). Mean P4 concentrations in ewes treated withhCG showed no differences according to the size of the follicle from which acc-CL were generated(P ˃ 0.05). In conclusion, administration of hCG or GnRH on day 4 post FTAI induced the formation of oneacc-CL from follicles of 3, 4 or 5 mm, indistinctly. However, serum P4 concentration increased significantlyonly in the hCG group. The serum P4 concentrations of acc-CL that originated from different folliclesizes did not differ.