Improving fertility to AI in Bos indicus cattle

Summary

​Increasing circulating concentrations of progesterone before AI has been shown to improve pregnancy rates to AI, but reduced follicle diameters and pregnancy rates to timed AI in some studies. Fertility in dairy cows has also been positively associated with antral follicle counts (AFC's). Three experiments were conducted in Bos indicus heifers and cows to determine if increasing circulating concentrations of progesterone during preovulatory follicular development or differences in AFC's could affect fertility to AI.

reater circulating concentrations of progesterone increased the odds of pregnancy to AI in anovulatory females but had variable effects on fertility in ovulatory animals, decreasing the odds of pregnancy in one year but not another.

Treatment with greater doses of progesterone in combination with administration of oestradiol benzoate delayed new wave emergence and reduced the diameter of emerging follicles when treatment with exogenous progesterone ended but did not significantly affect the growth rate of emerging follicles. Pregnancy rates to AI tended to be less in females with AFC's ≤ 4 compared to those with AFC's >4 . Manipulating concentrations of progesterone and AFC before AI has the potential to improve pregnancy outcomes to AI in Bos indicus females.