Use of Estradiol Cypionate in a Presynchronized Timed Artificial Insemination Program for Lactating Dairy Cattle

¹ Department of Animal Sciences, University of Florida, Gainesville, FL 32611
² Department of Animal Science, Texas A&M University at Dallas, Hico, TX
³ Department of Large Animal Clinical Sciences-College of Veterinary Medicine, University of Florida, Gainesville, FL 32611
⁴ Texas A&M University at Dallas, Hico, TX

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 PGF₂ (25 mg, im) given 14 d apart with TAI protocols beginning 14 d after the second injection of PGF₂. The TAI protocols consisted of an injection of GnRH (100 µg, im) followed by PGF₂ 7 d later. Then, cows either received an injection of GnRH (Treatment I, Ovsynch) at 48 h after PGF₂ and inseminated 16 to 24 h later or received an injection of ECP (1 mg, i.m.) at 24 h after PGF₂, (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.

Key Words: timed artificial insemination • estradiol cypionate • ovulation

Submitted on May 18, 2001
Accepted on August 30, 2001

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