Improving AI rates in Bos indicus heifers

Summary

​Artificial insemination (AI) provides a practical means by which improved genetics can be disseminated rapidly and efficiently throughout a beef cattle population. The problem in northern Australia is that AI is estimated to be utilised in less than 1% of extensively managed bull breeding herds.

The objectives of this project were to develop optimum methods of synchronising ovulation in rising 2–year-old Brahman heifers, investigate practical methods of increasing the proportion of heifers cycling at the commencement of an AI programme, and improve the ability of producers to select heifers likely to become pregnant to fixed-time AI (FTAI). Replacing oestradiol benzoate with gonadotrophin releasing hormone to synchronise follicular wave emergence and ovulation resulted in poorer pregnancy rates to FTAI.

Key factors affecting the likelihood of heifers becoming pregnant to FTAI were presence of a corpus luteum on the ovaries at the time of commencement of treatments to synchronise ovulation and the inherent fertility of the heifers. Becoming pregnant to FTAI was shown to be a heritable trait.