77 Evaluation of sexed semen on conception and pregnancy loss rates in synchronized Bos indicus, Bos taurus-indicus, and Bos taurus cows following timed artificial insemination

The present study aimed to evaluate oestrus expression, conception, and pregnancy loss rates following timed AI (TAI) with sexed or unsexed semen in beef cows. Postpartum suckled or dry Bos indicus (Brahman; n = 32), Bos taurus-indicus (Bonsmara; n = 33), and Bos taurus (Nguni; n = 30) cows from emerging cattle farmers in South Africa were assigned to a 9-day Ovsynch + controlled intravaginal drug release (CIDR^®) protocol followed by TAI. On a random day of the oestrous cycle (Day 0) cows received CIDR^® (1.9 g of progesterone, Pfizer Laboratories) inserts and 2 mL intramuscularly (IM) administration of oestradiol benzoate (EB, VTech). On Day 8, oestrus detection aids were applied with 2-mL intramuscular injection of prostaglandin F₂α (PGF₂α; Estrumate^®, Intervet) and CIDR^® removal. Cows received 1-mL IM injection of EB on Day 9. Oestrus expression was evaluated before TAI, and cows received TAI 55 h following CIDR^® removal with sexed or unsexed semen from four Angus sires. Pregnancy was diagnosed by transrectal ultrasonography 35, 65, and 95 days following TAI to determine pregnancy loss for first (between Days 35 and 65) and second (between Days 66 and 95) periods of pregnancy. Data were analysed using logistic regression procedure and chi-squared test to determine significant differences in the effect of oestrus expression and semen type on conception and pregnancy loss rates. Oestrus expression was similar for all cattle subspecies (P > 0.05). Conception rates and pregnancy losses were compared within and across per cattle subspecies (indicus vs taurus indicus vs taurus), per day (35, 65, 95), and per semen type (sexed vs nonsexed). It was concluded that conception and pregnancy loss rates vary among cattle subspecies when utilising sexed semen.