Estrus manifestation and pregnancy rate in Tropical Milking Criolloheifers synchronized with a low dose of PGF2 α

In order to determine estrus manifestation and pregnancy rates in Tropical Milking Criollo (CLT) heifers synchronized to estrus with a low dose (12,5 mg) of PGF2 α fifty-four cyclic virgin CLT heifers were randomly assigned to two treatments: 1) Low dose (DB; n=27): i.m. injection of 12,5 mg PGF2 α; and 2) Complete dose (DC, n=27; control group): i.m. injection of 25 mg PGF2 α. From 12 h after PGF2 α and during five days estrus was detected every 4 h for 30 min to determine the start and end of estrus, estrus duration and estrus manifestation rate. Heifers were artificially inseminated (IA) 12 h after estrus detection and were monitored by transrectal ultrasonography every 4 h from the end of estrus until ovuation to determine time and rate of ovulation. Repeat breeder heifers received a second IA service. Pregnancy was diagnosed 45 days after IA. Estrus manifestation and ovulation rates were 100% in both treatments. No significant (P>0.0%) difference was found among treatments for time of estrus and ovulation, estrus duration or pregnancy rate at first IA service. Pregnancy rate at second IA service and overall pregnancy rate were significantly (P<0.05) higher for DB than for DC (77.7% and 74% vs 30% and 37%), respectively. Estrus synchronization with a low dose of PGF2α resulted in an acceptable overall pregnancy rate in CLT heifers, which is reflected in a lower cost of the estrus synchronization program.