Hormonal treatment post insemination for induction of accessory corpora lutea and production of progesterone in sheep

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

Foz do Iguazu

Simposio; 10th International Ruminant Reproduction Symposium; 2018

Colegio Basileiro Reproducao Animal

Different therapeutic strategies have been used with the objective of increasing the concentration of progesterone (P4) and improving luteal function. Hormonal treatments in sheep were carried out in different breeds, animal categories and seasons of the year, using gonadotrophin releasing hormone (GnRH) or human chorionic gonadotrophin (hCG) in the early or late luteal phase. The aim of the study was to evaluate the effect of the administration of GnRH or hCG at day 4 post fixed-time artificial insemination (FTAI) on the induction and maintenance of accessory corpora lutea (acc-CL) and on the production of serum P4 concentration. Multiparous adult Merino ewes (n= 36) were treated for estrus synchronization using intravaginal progestagen sponges (60 mg of MAP; Progespon®, Syntex, Argentina), during 14 days and a single dose of equine Chorionic Gonadotropin (200 IU of eCG, i.m.; Novormon®, Syntex, Argentina) was applied at the end of progestagen treatment. At 53-56 h after pessary removal, FTAI was performed vaginally with a dose of 100 million spermatozoa of fresh semen. The ewes were assigned randomly to three groups on day 4 post FTAI: 1. GnRH group (n= 12, 4 μg of analogue of GnRH, i.m., Buserelin, Receptal®, Intervet, Argentina), 2. hCG group (n= 12, 300 IU of hCG, i.m., Gonacor®, Ferring, Argentina) and 3. Control group (n= 12, 1 ml of saline solution, i.m.). Laparoscopic observation of the ovaries at day 4, 10 and 21 post FTAI was performed to determine the presence of ovulatory CL (days 4, 10 and 21) and acc-CL (days 10 and 21). Serum P4 concentration was assessed by chemiluminescence on days 4, 7, 10, 14, 17, 21, 28 and 35 post FTAI. The number of acc-CL was compared by one-way ANOVA. The serum P4 concentration in pregnant ewes was analyzed by a generalized linear model with time-repeated measurements. Statistical significance was accepted from P