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

FERNANDEZ J; BRUNO GALARRAGA MACARENA; DE LA SOTA, L; CUETO MARCELA; LACAU, I.M.; GIBBONS A,

Foz Iguazu

Simposio; International Ruminant Reproduction Symposium; 2018

SBTE

Different therapeutic strategies have been used with the objective of increasing the concentration ofprogesterone (P4) and improving luteal function to reduce embryonic losses. Hormonal treatments insheep were carried out in different breeds, animal categories and seasons of the year, using gonadotrophinreleasing hormone (GnRH) or human chorionic gonadotrophin (hCG) in the early or late luteal phase. Theaim of the study was to evaluate the effect of the administration of GnRH or hCG at day 4 post fixed-timeartificial insemination (FTAI) on the induction and maintenance of accessory corpora lutea (acc-CL) andon the production of serum P4 concentration. Multiparous Merino ewes (n= 36) were treated for estrussynchronization using intravaginal progestogen 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 administered at the end of progestagen treatment. At 53-56 h aftersponge 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 ofGnRH, 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.). Laparoscopicobservation of the ovaries at day 4, 10 and 21 post FTAI was performed to determine the presence ofovulatory CL (days 4, 10 and 21) and acc-CL (days 10 and 21). Serum P4 concentration was assessed bychemiluminescence on days 4, 7, 10, 14, 17, 21, 28 and 35 post FTAI. The number of acc-CL wascompared by one-way ANOVA. The serum P4 concentration in pregnant ewes was analyzed by ageneralized linear model with time-repeated measurements. Statistical significance was accepted fromP<0.05. The hCG group showed higher mean concentrations of P4 on days 7, 10, 14, 21, 28 and 35 postFTAI compared with the GnRH group and the Control group (P<0.05), while no differences wereobserved between these two latter groups (P>0.05). In all groups, an increase of serum P4 concentrationwas observed on day 35 post FTAI (P<0.05). The presence of an acc-CL was observed in 85 and 50 % ofewes treated with hCG or GnRH, respectively, whereas no ewes with an acc-CL were observed in theControl group (P<0.05). The hCG group had higher concentration of P4 in the animals that had an acc-CLcompared to those that did not generate acc-CL (P<0.05), while no differences were observed in theGnRH Group (P>0.05). The acc-CL were maintained until 21 days post FTAI in pregnant sheep treatedhormonally. In conclusion, administration of hCG or GnRH at 4 days post FTAI induced and maintainedthe formation of an acc-CL. However, serum concentration of P4 increased only in the hCG group andmaintained until day 35 post FTAI. Differences in the pharmacodynamics of these two hormones mightinduce acc-CL with different steroidogenic capacity. Further research should be done to assess the effectof these hormones on the histological and functional characteristic of acc-CL. Funded by Projects PNSA1115053 (INTA) and PICT 2012-2238 (FONCyT).