Effects of postpartum energy balance, body condition score, and insemination time on conception rates of Bonsmara cows bred using timed artificial insemination

Fertility management of extensively farmed beef cattle in South Africa is essential to ensure the economic viability of such production systems. However, the success of timed artificial insemination (TAI) programmes varies, affecting cattle farmers' adoption of this reproductive technique. This study investigated the effects of postpartum energy balance (∆M), body condition score (BCS), time of artificial insemination (morning or afternoon), and any interactions on the conception rates of Bonsmara cows (N = 72, second to ninth parity, BCS ≥2.25) in the Limpopo Province of South Africa. The cows were synchronised in the morning or afternoon using the seven-day CO-Synch synchronisation protocol. Cow live weight and BCS were recorded at synchronisation, TAI, and pregnancy determination, and the data were used to calculate the ∆M. Cows that did not conceive from TAI were naturally mated, and the number of cows that did not conceive was recorded. The average conception rate of cows bred by both TAI and natural mating was 76.7 ± 5.60%. The ∆M and time of artificial insemination did not influence the conception rate. The BCS and duration of the postpartum period influenced the conception rates of cows bred by TAI and cows bred by combined TAI and natural mating. Cows that conceived from TAI tended to have higher estimated breeding values for fertility than those that conceived from natural mating or did not conceive. Cows with a BCS of 3.00–3.75 had the highest conception rates, followed by those with a BCS >3.75, with cows with a BCS <2.75 having the lowest rates. (Submitted 4 August 2025; Accepted 19 August 2025; Published 10 October 2025)