126 Effect of oestrus synchronisation protocol with a high dose of oestradiol and an intravaginal progesterone-releasing device on the endometrial epidermal growth factor concentrations and fertility in recipient cows

Epidermal growth factor (EGF) concentrations in the endometrium show two peaks on Days 2–4 and 13–14 of the oestrous cycle in fertile cows. The absence of the peaks has been linked to reduced fertility in repeat breeder cows. We have reported that a combined treatment with a high dose of oestradiol and an intravaginal progesterone-releasing device restored the EGF peaks and fertility in repeat breeder cows, although the EGF peak concentrations remained in the low area within the normal range. Further, it remained to be studied whether this treatment enhances the peaks and improve fertility in apparently normal cows. Thus, the present study examined this using Holstein cows selected as embryo transfer (ET) recipients. Recipients were Holstein multiparous lactating cows between 60 and 125 days postpartum. Cows were selected by following criteria: endometrial cytology (PMN < 5%), normal cyclicity, ovulation within 48 h after the onset of the oestrus, presence of a corpus luteum > 2.0 cm, and a follicle between 1.0 cm and 2.0 cm on Day 7 of the oestrous cycle. Cows were synchronised for oestrus with either a single injection of prostaglandin F2 α (control) (n = 87) or a combination of 5 mg oestradiol benzoate and PG at the insertion and removal of an intravaginal progesterone-releasing device 9 days apart (EB-P4-PG, n = 89), a protocol that had been reported to restore the EGF peak in RB cows. Cows were subjected to uterine endometrial biopsy for EGF assay on Day 3 (Day 0 = oestrus) and ET with a frozen-thawed embryo on Day 7. Pregnancy was diagnosed by palpation per rectum on Day 60 or later. EGF concentrations were compared by Student’s t-test and proportion of cows with the normal EGF peak and conception rate were compared by χ² analysis. EB-P4-PG treatment increased the proportion of recipient cows with the EGF peak (>4.70 ng/g tissue weight, 80.5% vs 93.3%; P < 0.05) and high EGF peaks (>7.50 ng/g tissue weight, 21.8% vs 40.4%; P < 0.05). Conception rate of cows with high EGF peaks tended to be higher than those with mid peak concentrations (4.70–7.50 ng/g tissue weight; P < 0.09). The present results indicate that recipient cows selected by widely used criteria include ∼20% of low fertility cows due to an absence of the EGF peak. Use of EB-P4-PG treatment increases the proportion of recipient cows with the EGF peak. The treatment also increased the proportion of cows with high EGF peaks that may show higher fertility. Therefore, use of EB-P4-PG treatment for oestrus synchronisation in recipient cows may increase conception rate after ET.