Ovarian follicular dynamics in purebred and crossbred Boran cows in Ethiopia

Boran is an endangered breed of cattle indigenous to Ethiopia and the relatively poor understanding of its reproductive physiology has impeded efforts to maximize reproductive performance of the breed. This study characterized ovarian follicular dynamics in 9 purebred Boran and 8 Boran×Holstein (B×H) crossbred cows. Ovaries of all 17 cows were examined once per day for 61 consecutive days (encompassing three periods of estrus) using transrectal ultrasonography. The mean (±standard error of mean) inter-ovulatory interval (IOI) was similar (P>0.05) in Boran (19.4 ± 0.2 days) and B×H cows (20.1 ± 0.4 days). Two (in 79% of estrous cycles) or three (in 21% of cycles) follicular waves per IOI were observed and IOI was shorter (P0.10) in both genotypes (15.8 ± 1.5 mm in Boran and 19.4 ± 2.9 mm in B×H). Boran cows possessed a greater (P<0.001) total number of ovarian follicles than BxH cows and both genotypes displayed more (P<0.05) activity on their right than left ovary. Results of our study have provided novel insights into the normal reproductive physiology of the Boran breed.