Effect of GnRH or hCG administration on Day 4 post insemination on reproductive performance in Merino sheep of North Patagonia

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

THERIOGENOLOGY

ELSEVIER SCIENCE INC

Año: 2019 vol. 126 p. 63 - 67

0093-691X

Different therapeutic strategies have been used with the objective of improve luteal function to reduceembryonic losses. The objective of this work was to study the effect of the administration of GnRH or hCGat Day 4 post fixed time artificial insemination (FTAI) on reproductive efficiency in Merino sheep duringthe breeding season in North Patagonia. Estrus of multiparous Merino ewes (n ¼ 288) was synchronizedby two injections of prostaglandins (PG; 125 mg, Cloprostenol), 14 days apart. Cervical FTAI was performed53e56 h after the second PG with a dose of fresh semen (100 106 spermatozoa) from fiveMerino rams. In all ewes body condition score (BCS) was determined at FTAI. At 4 days post FTAI eweswere randomly assigned into three experimental groups: GnRH group (4 mg, Buserelin; n ¼ 99), hCGgroup (300 IU, hCG; n ¼ 92) and Control group (1 ml, saline solution; n ¼ 97). Pregnancy and pregnancylosses were evaluated by ultrasonography on Days 33 and 90 post FTAI. Additionally, embryo crownrumplength (CRL) was measured by ultrasonography (n ¼ 12 single-pregnant ewes by experimentalgroup) at the first ultrasound. Date of birth, litter size and lamb weight were recorded (n ¼ 111 pregnantewes). Pregnancy rate on Days 33 and 90 post FTAI did not differ among treatment groups (P > 0.05).Pregnancy losses at Day 33 post FTAI were lower in the hCG group compared to the GnRH and Controlgroups (0, 3, 7.2%, respectively; P < 0.05). Pregnancy losses between Days 33 and 90 after FTAI werenegligible (P > 0.05). The embryo CRL at Day 33 post FTAI was not increased by the hormonal treatments(P > 0.05). Moreover, it was lower in GnRH group compared to Control group (P < 0.05). Litter size tendedto be greater in the GnRH group compared to the hCG and Control groups (P < 0.1). The birth weight oftwin lambs tended to be higher in the GnRH group compared to the Control group (P < 0.1). The birthweight of single lambs was not affected by treatments (P > 0.05). Ram fertility and BCS of ewes at FTAIinfluenced the effect of hormonal treatments on reproductive parameters. In conclusion, administrationof hCG or GnRH at Day 4 post FTAI does not improve pregnancy rate but treatment with hCG reducespregnancy loss on Day 33 post FTAI. GnRH treatment improves litter size and twin lambs birth weight.