Abstract
The fertility of Boran cattle was determine followed artificial insemination (AI) at different times from the onset of induced oestrus. 46 animals were inseminated 6, 12 and 18 h after observed oestrus which was induced with a single injection of 25 mg prostaglandin F2 alfa (PGF2a: Luthalyse)2. Animals failing to respond were given a second injection after 12 days and insemination at a fixed time, 72 h later. Ten animals served as untreated controls and were inseminated 12 h after observed natural oestrus during a 22-day breeding period. Overall oestral response to PGF2a treatment was 72%. Oestrus was observed an average of 76.9 ± 42.8 h after treatment. The pooled mean pregnancy rate (PR) was 37.5% and was significantly affected (P<0.05) by AI time but not age group, bull or AI technician. PR was highest (56%) in animals insemination 6 h after observed oestrus, similar to the 60% in the control animals. The lowest pregnancy rates (33%) were in animals insemination either 12 or 18 h after induced oestrus. It was concluded that PGF2a treatment of Boran cows leads to earlier ovulation and fertilization, and treated animals need to be inseminated earlier than after natural oestrous.
