Abstract
Resynchronizing estrus and ovulation in open cows and heifers (2004)
Highlights
Earlier identification of nonpregnant females is one way to reduce prolonged interinsemination intervals that occur because of poor efficiency in detecting post-insemination estrus
Females received PGF2" 7 days later and were assigned randomly to either receive estradiol cypionate (ECP) 24 hours after PGF2" or a second GnRH injection after PGF2". Those detected in estrus were inseminated, whereas the rest received a timed AI (TAI) between 65 and 74 hours after PGF2"
Conception rates tended to be greater for females inseminated after estrus (37%) than after TAI (29%), and the tendency was more pronounced for those treated with Heatsynch (41 vs. 27%) than for those treated with Ovsynch (33 vs. 31%)
Summary
Earlier identification of nonpregnant females is one way to reduce prolonged interinsemination intervals that occur because of poor efficiency in detecting post-insemination estrus. Treating nonpregnant cows with PGF2" between 27 and 29 days after a previous AI induced regression of the corpus luteum (CL) before subsequent insemination after detected estrus or timed AI (TAI), and reduced days to re-insemination and to conception. Applying the Ovsynch protocol or substituting estradiol cypionate (ECP) for GnRH in an Ovsynch-like protocol (known as Heatsynch) are viable options. Administering ECP to females in proestrus has been found to induce estrus, preovulatory LH surge, ovulation, and normal corpus luteum (CL) development in dairy heifers and dairy cows. Two previous studies have found that conception rates of Heatsynch-treated heifers are not different from those in heifers inseminated after detected estrus, and those in lactating cows after Heatsynch are similar to those after Ovsynch
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