Evaluation of artificial insemination success in Ankole and crossbred cows under natural and induced oestrus conditions in Rwanda

The study assessed the pregnancy outcomes in Ankole and crossbred cows and heifers following artificial insemination (AI) during either natural oestrus or hormonally induced oestrus under Rwanda field conditions. A total of 351 clinically healthy cows and heifers were enrolled between 2020 and 2022 from four districts covering three agro-ecological zones. Of these, 214 animals underwent oestrus synchronisation using PRID Delta® devices in combination with GnRH and prostaglandin, while 137 were inseminated upon detection of natural oestrus. Pregnancy diagnosis was performed 70 days post-AI using transrectal ultrasonography. Cows inseminated on observed natural oestrus had a significantly higher pregnancy rate (62.8%) than those synchronised (29.4%; P ≤ 0.01). Breed, age, body condition score (BCS), oestrus intensity, and AI timing were all significantly associated with fertility outcomes. Cross-Jersey cows achieved the highest pregnancy rate under natural oestrus (91.3%), while cross-Friesians had the lowest under synchronisation (23.9%). Ankole cows showed better fertility under synchronisation (54.5%) than under natural oestrus (35.0%). Among naturally cycling cows, AI performed 7 – 12 hours after oestrus detection resulted in the highest pregnancy (77.9%), and cows with BCS of 2.5 – 3.0 conceived more successfully. In synchronised females, clear oestrus signs were linked to improved pregnancy (35.1%), while silent oestrus yielded poor results (8.7%). These findings highlight the reproductive advantage of natural oestrus detection in smallholder systems and emphasise the need to adapt AI strategies based on breed, BCS, and oestrus expression.