Efficacy of Short-Term Timed Artificial Insemination Protocols With Estradiol Esters and PGF2α in Girolando Cows

Using a synchronisation protocol based on estradiol esters and prostaglandin, established in cattle since the 1970s, we implemented 24 or 48-h intervals between hormone administration and timed artificial insemination (TAI). This study compared two short-duration TAI protocols using estradiol benzoate (EB) and cypionate (EC) as ovulation inducers. A total of 172 Girolando female cows were selected after ovarian ultrasonographic evaluation and received 500 microg of prostaglandin F2α (PGF) at the start of the treatment (D0). The inclusion criterion for females in the study was the presence of a corpus luteum measuring ≥ 14 mm and at least one follicle with a diameter between 8 and 20 mm. The cows were randomly sorted into two treatment groups. The EB group received 2 mg of EB 24 h after PGF (D1), and TAI was performed 24 h later (D2). The EC group received 2 mg estradiol cypionate simultaneously with PGF, and TAI was performed 48 h later. Pregnancy was diagnosed 30 days after AI using transrectal ultrasonography. Experiment I evaluated follicular dynamics in 18 females (EB: n = 9; EC: n = 9) by analysing the follicular growth rate, pre-ovulatory follicle (POF) diameter, ovulation timing and ovulation rate. No statistically significant differences were observed (p > 0.05), with a 77.8% ovulation rate in both treatments. Experiment II compared the conception rates in 172 females (EB: n = 85; EC: n = 87). The overall conception rate was 30.2%, with no significant difference between the treatments (EB: 27.1%; EC: 33.3%). However, cows with a body condition score < 3.0 tended to have higher conception rates with EC than with EB (39.1% vs. 18.2%; p = 0.06). Cows with POF ≥ 10 mm at D0 had significantly higher conception rates with EC than with EB (48.3% vs. 29.0%; p = 0.03). Both protocols were equally effective; however, EC was more advantageous for cows with a POF ≥ 10 mm at treatment initiation.