Time of artificial insemination and pregnancy rates in Boran (Bos indicus) cattle

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.