Estrus synchronization and artificial insemination of hair sheep ewes in the tropics

Abstract

Hair sheep ewes (St. Croix White and Barbados Blackbelly) were used to evaluate 3 methods of estrus synchronization for use with transcervical artificial insemination (TAI). To synchronize estrus, ewes (n = 18) were treated with PGF2α (15 mg, im) 10 d apart, with controlled internal drug release (CIDR) devices containing 300 mg progesterone for 12 d (n = 18), or with intravaginal sponges containing 500 mg progesterone for 12 d (n = 18). On the day of the second PGF2α injection or at CIDR or sponge removal, sterile rams were placed with the ewes. Jugular blood samples were collected from the ewes at 6-h intervals until the time of ovulation, and daily for 16 d after estrus (Day 0). Plasma was harvested and stored at −20°C until LH, and progesterone concentrations were determined by RIA. There was no difference (P > 0.10) in time to estrus among the CIDR-, PGF2α- or sponge-treated ewes. All of the ewes in the CIDR group and 94.4% of the sponge treated ewes exhibited estrus by 36 h after ram introduction, while only 72.2% of PGF2α-treated ewes showed signs of estrus by this time (P < 0.06). The time from ram introduction to ovulation was not different (P > 0.10) among the CIDR-, PGF2α- or sponge-treated ewes. The time to the preovulatory LH surge was similar (P > 0.10) among CIDR, PGF2α and sponge treated ewes. Progesterone levels through Day 16 after the synchronized estrus were not different (P > 0.10) among treatment groups. Hair sheep ewes (n = 23) were synchronized using PGF2α and bred by TAI using frozenthawed semen 48 h after the second injection. The conception rate to TAI was 2 23 (8.7%) and produced 3 ram lambs. In a subsequent trial, 17 ewes were synchronized with CIDR devices and bred by TAI using frozen-thawed semen 48 h after CIDR removal, resulting in a conception rate of 52.9 % ( 9 17 ). It is possible to synchronize estrus in hair sheep using either CIDRs, sponges or PGF2α. Even though there were no significant differences in the timing of ovulation or the LH surge among the treatment groups, a higher conception rate was achieved in ewes synchronized with CIDR devices during the second trial. This may reflect an increase in the skill level of the TAI technician.