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

Hair sheep ewes (St. Croix White and Barbados Blackbelly) were used to eval uate 3 methods of estrus synchronization for use with transcervical artific ial insemination (TAI). To synchronize estrus, ewes (n = 18) were treated w ith PGF2 alpha (15 mg, im) 10 d apart, with controlled internal drug releas e (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 t he day of the second PGF2 alpha injection or at CIDR or sponge removal, ste rile rams were placed with the ewes. Jugular blood samples were collected f rom 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 degrees C u ntil LH, and progesterone concentrations were determined by RIA. There was no difference (P > 0.10) in time to estrus among the CIDR-, PGF2 alpha- or sponge-treated ewes. All of the ewes in the CIDR group and 94.4% of the spo nge treated ewes exhibited estrus by 36 h after ram introduction, while onl y 72.2% of PGF2 alpha-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-, PGF2 alpha- or sponge-treated ewes. The time to the preovulatory LH surge was similar (P > 0.10) among CIDR, PGF2 alpha and spo nge 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 PGF2 alpha and bred by TAI using frozen-thawed 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 PGF2 alpha. Even though there were no significant differ ences in the timing of ovulation or the LH surge among the treatment groups , a higher conception rate was achieved in ewes synchronized with CIDR devi ces during the second trial. This may reflect an increase in the skill leve l of the TAI technician. (C) 1999 by Elsevier Science Inc.