Effect of oestrus expression and eCG treatment on reproductive performance in dairy cows subjected to Progesterone plus Ovsynch protocol

The objectives were to evaluate the effects of equine chorionic gonadotropin on oestrus expression and fertility in dairy cows undergoing a timed artificial insemination protocol. Holstein cows (n =534) were subjected to a 7-day progesterone-based Ovsynch protocol. The equine chorionic gonadotropin group received 500 IU equine chorionic gonadotropin at progesterone device removal, whereas the control group received no additional treatment. Oestrus expression was monitored using an electronic neck-mounted activity system and recorded during the voluntary waiting period-oestrus expression and during synchronization prior to timed artificial insemination (pre timed artificial insemination-oestrus expression). The overall pre timed artificial insemination-oestrus expression rate during synchronization was 36.3 %. Administration of equine chorionic gonadotropin did not (P > 0.05) influence the pre timed artificial insemination-oestrus expression (36.0 vs. 36.7 %) and pregnancy per artificial insemination at day 30 (36.7 vs. 36.7 %). In addition, pregnancy loss, calving rate, and twinning rate did not differ between equine chorionic gonadotropin and control groups (P > 0.05). During the voluntary waiting period, 59.0 % of cows expressed oestrus. Pregnancy per artificial insemination was greater (41.3 % vs. 32.4 %) in voluntary waiting period-oestrus expression positive cows than voluntary waiting period- oestrus expression negative cows (P = 0.04) regardless of group (equine chorionic gonadotropin and control). However, there was no significant difference in pre timed artificial insemination- oestrus expression between equine chorionic gonadotropin and control groups in voluntary waiting period-oestrus expression negative (P = 0.33) and voluntary waiting period- oestrus expression positive cows (P = 0.91). Similarly, treatment with equine chorionic gonadotropin did not affect pregnancy per artificial insemination, either in voluntary waiting period-oestrus expression–negative cows (P = 0.39) or in voluntary waiting period-oestrus expression –positive cows (P = 0.69). In conclusion, oestrus expression during the voluntary waiting period-oestrus expression and prior to timed artificial insemination-oestrus expression had a strong association with higher fertility. However, equine chorionic gonadotropin did not enhance fertility outcomes in high-producing dairy herds using sex-sorted semen within an optimised synchronization protocol, regardless of parity or cyclicity status.