Fixed timed artificial insemination and early resynchronization of ovulation in different categories of ewes in grazing system: Response of multiparous, nulliparous, and lactating ewes during the breeding season

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The aims of this study were to: 1) determine if the insertion of a second MAP sponge in ewes 12 days after the first FTAI affects the pregnancy rate; 2) compare the responses to resynchronization protocol in multiparous and nulliparous ewes; and 3) compare the responses to resynchronization protocol in multiparous and postpartum lactating ewes. Three trials were performed with 186 Corriedale ewes: 111 multiparous [(control – CON (n = 60) and synchronization – SYNC groups (n = 51)], forty-two 1.5 yr-old nulliparous (group NUL), and 33 lactating ewes with at least 28 postpartum (group PtP). All ewes were treated with a MAP sponge for 6 days. Twenty-four hours before the sponge withdrawal, all animals received 0.24 mg of cloprostenol sodium and 300 IU of eCG, and 0.05 mg of gonadorelin 36 h after sponge withdrawal and artificially inseminated (AI) 27-30 h after the GnRH administration (Day 0). A second intravaginal sponge was inserted to all groups (except for SYNC group), on Day 12. On Day 17, early pregnancy diagnosis was performed with doppler ultrasound in all ewes. Sponge withdrawal occurred on Day 18, and a new GnRH dose (0.05 mg) was administrated 36 h after it. Once again, AI 27-30 h after the GnRH administration. A final pregnancy diagnosis on Day 42 was performed in all ewes for confirmation of first diagnosis and the data were confirmed by parturition. Ewes in all groups presented estrus signs (SYNCH – 94.1%; CON – 71.7%; NUL – 83.3%; PtP – 39.4% at first AI and CON – 65.2%; NUL – 76.5%; PtP – 62.5% at the second). Pregnancy rate and pregnancy loss were not different between synchronized and resynchronized multiparous ewes (SYNCH – 56.9% vs. CON – 58.3% pregnant at D42 and SYNCH – 5.9% vs. CON – 7.1% fetal loss at D42). No differences were found between resynchronized multiparous and nulliparous ewes at the first FTAI, only fecundity was higher in multiparous ewes [CON – 0.88 vs. NUL – 0.62 (P = 0.04)]. Resynchronized multiparous ewes had higher reproductive performance than postpartum ewes that only presented pregnancy after the second FTAI [CON – 73.3% vs. PtP – 15.1% total pregnancy (P = 0.003)]. Overall, synchronization-resynchronization FTAI treatments may be included in reproductive programs in nulliparous ewes, but the treatments cannot superimpose to the limiting conditions imposed by postpartum lactating status. The resynchronization treatments allow to include practical managements with no deleterious effects in the results of the first FTAI.