192 The use of human chorionic gonadotropin seven days after synchronized estrus for the increase of luteal tissue in Morada Nova ewes

Abstract

The study was performed to evaluate whether the use of hCG 7 days after synchronized oestrus in Morada Nova ewes would increase the number and size of corpora lutea. Multiparous Morada Nova ewes (n=115, mean weight of 36.6kg, body condition score 3.13 on 1 to 5 scale) were used. Oestrus was synchronized by using an intravaginal sponge impregnated with medroxyprogesterone acetate (60mg, Progespon®, Zoetis, Parsippany, NJ, USA) for 6 days and eCG (200IU, IM Novormon®, Zoetis) plus PGF2α analogue (37.5μg, D-cloprostenol, IM, Vetglan®, Hertape Calier, Spain), both administered 24h before the sponge removal. Seven days after the synchronized oestrus, hCG (300IU, IM, Vetecor®, Hertape Calier; n=57) or normal saline (control group, 1mL, IM, 0.9% NaCl, Eurofarma Laboratory SA, Sao Paulo, Brazil; n=58) was injected. B-mode ultrasound examinations of the ovaries were performed using the equipment MyLab Vet 30 Gold (Esoate, Genoa, Italy) on Day 7 (corresponding to the day of hCG or physiological solution administrations), and 6 days later (Day 13). The number of corpora lutea present and the size of luteal tissue (sum of diameter and area) were determined. Data were analysed by ANOVA with Tukey’s post hoc test (mean±s.e.m.) using SAS software (SAS Institute Inc., Cary, NC, USA). On Day 7, the number of corpora lutea was similar (P>0.05) between the hCG and control groups (1.58±0.09v. 1.57±0.08, respectively); however, the number was higher on Day 13 (P<0.05) in the hCG group (2.65±0.13) than in the control group (1.69±0.07). Similarly, there was no difference (P>0.05) between groups in diameter (16.9±0.82v. 16.0±0.71mm) and area (1.61±0.07v. 1.45±0.06cm2) for hCG and control groups, respectively, on Day 7. Differences were observed on Day 13, such that the hCG ewes had luteal tissue of larger (P<0.0001) diameters (27.13±1.25v. 18.44±0.85mm) and area (2.81±0.13v. 1.71±0.08cm2) than ewes of the control group. In conclusion, 300IU of hCG injected 7 days after synchronized oestrus is effective to increase the number of corpora lutea and in the size of luteal tissue. Despite indications of a favourable effect on luteal dynamics, the effects on progesterone production and conception rate need to be examined. This study was supported by CNPq and EMBRAPA (process no. 02.13.06.026.00.02).