COMPARISON BETWEEN ESTRADIOL CYPIONATE AND GONADOTROPIN RELEASING HORMONE AS OVULATION SYNCHRONIZATION TREATMENTS FOR FIXED-TIME ARTIFICIAL INSEMINATION PROGRAMS IN BRAHMAN-CROSS HEIFERS IN A SUBTROPICAL REGION OF NORTHEASTERN MEXICO

Abstract

Synchronization protocols with intravaginal progesterone releasing devices (CIDR) and PGF2α were evaluated, with GnRH or estradiol cypionate (ECP) added for fixed-time artificial insemination (FTAI) in five counties in Tamaulipas, Mexico. Brahman-cross heifers (≥15 months old) were selected based on body condition (≥3 on a 5-point scale) and confirmed ovarian activity. The six treatments (n = 320 each) were: T1 (9-d CIDR, ECP on insertion, PGF2α on day 9, ECP on day 10, FTAI 54 h after removal); T2 (7-d CIDR, ECP on insertion, PGF2α on day 7, ECP on day 8, FTAI 54 h after removal); T3 (7-d CIDR, GnRH on insertion, PGF2α on day 7, FTAI and GnRH 48 h after removal); T4 (7-d CIDR, GnRH on insertion, PGF2α on day 6, FTAI and GnRH 48 h after removal); T5 (7-d CIDR, GnRH on insertion, PGF2α on day 7, FTAI and GnRH 60 h after removal); and T6 (7-d CIDR, GnRH on insertion, PGF2α on day 7, FTAI alone 48 h after removal). Pregnancy was diagnosed ultrasonically 45 days after FTAI. Analyses included pregnancy rates and treatment costs (hormones and handling). Pregnancy rates ranged from 31.6 ± 3.9 to 48.0 ± 10.6%; neither treatment nor county affected these rates (p > 0.05). In conclusion, the inclusion of treatment costs showed two more economical treatments (T2 using estradiol or T3 using GnRH) under the nutritional, weather and handling conditions present in the tropical region of southeastern Tamaulipas.