Use of estradiol cypionate in a presynchronized timed artificial insemination program for lactating dairy cattle

Abstract

Experiment 1 evaluated pregnancy rates when estradiol cypionate (ECP) was used to induce ovulation as part of a timed artificial insemination (TAI) protocol in comparison to Ovsynch for lactating dairy cows in Florida (n = 371) and Texas (n = 321). Cows were presynchronized with two injections of PGF 2α (25 mg, im) given 14 d apart with TAI protocols beginning 14 d after the second injection of PGF2α. The TAI protocols consisted of an injection of GnRH (100 μg, im) followed by PGF 2α 7 d later. Then, cows either received an injection of GnRH (Treatment I, Ovsynch) at 48 h after PGF2α and inseminated 16 to 24 h later or received an injection of ECP (1 mg, i.m.) at 24 h after PGF2α, (Treatment II; Heatsynch) and inseminated 48 h later. In Florida, pregnancy rates after TAI were 37.1 ± 5.8% for Ovsynch compared with 35.1 ± 5.0% for Heatsynch. In Texas, pregnancy rates were 28.2 ± 3.6% for Ovsynch and 29.0 ± 3.5% for Heatsynch. Overall pregnancy rates did not differ between Ovsynch and Heatsynch treatments. In Experiment 2, estrus and ovulation times were determined in lactating dairy cows submitted to the Heatsynch protocol. Frequencies of detected estrus and ovulation after ECP were 75.7% (28/37) and 86.5% (32/37), respectively. Mean intervals to ovulation were 55.4 ± 2.7 h (n = 32) after ECP and 27.5 ± 1.1 h (n = 27) after onset of estrus. Estrus occurred at 29.0 ± 1.8 h (n = 28) after ECP. It is recommended that any cow detected in estrus by 24 h after ECP injection be inseminated at 24 h and all remaining cows be inseminated at 48 h because 75% (n = 24/32) of the ovulations occurred between ≥ 48 h to ≤ 72 h after ECP. Synchronization of ovulation and subsequent fertility indicated that estradiol cypionate could be used to induce ovulation for successful timed insemination.