Effect of reproductive methods and GnRH administration on long-term protocol in Santa Ines ewes.

Abstract

This study aimed to determine whether reproductive performance of ewes submitted to laparoscopic timed artificial insemination (TAI) would be similar to ante meridiem (AM)/post meridiem (PM) rule and assisted natural mating (NM), and whether GnRH may enhance the pregnancy rate in TAI. In experiment I, 191 non-lactating ewes were synchronized, then TAI was performed either 48h after progesterone (P4) removal (TAI-48h) or 12h after estrus detection (AM/PM); moreover, some ewes were submitted to NM (NM) as control treatment. In experiment II, 247 non-lactating ewes were allocated in five treatments, a control (no-GnRH on protocol) and four treatments arranged in a factorial design 2×2. The factors were time and dose of GnRH: ewes that received either 10μg (TAI-10μg-36h) or 25μg of GnRH (TAI-25μg-36h) 36h after P4 removal and ewes that received either 10μg (TAI-10μg-48h) or 25μg of GnRH (TAI-25μg-48h) at time of insemination, 48h after P4 removal. In experiment I, pregnancy rate in TAI-48h was lower (P=0.03) than AM/PM and NM. Moreover, the probability of pregnancy in TAI-48h was higher (P=0.06) in ewes detected in estrus early. In experiment II, the use of GnRH in TAI protocols increased (P<0.01) pregnancy rate at synchronization, and TAI-25μ-48h and TAI-10μg-36h treatments increased (P=0.02) pregnancy rate compered to TAI-10μg-48h. We conclude that TAI decreased pregnancy rate compered to NM and AM/PM, which may be improved by GnRH use in TAI to synchronize ovulation.