Ovarian follicular dynamics in purebred and crossbred Boran cows in Ethiopia

Abstract

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 (P<0.001) for cows with two follicular waves per estrous cycle (n=27; 19.5 ± 0.9 days) than for cows with three (n=7; 20.9 ± 2.1 days). All Boran cows (100%) exhibited two waves of follicular growth per estrous cycle and this was higher (P<0.001) than the proportion observed in B×H cows (56%). Mean diameter of the dominant follicle was similar (P>0.10) 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 B×H 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.

Keywords: Boran, estrous cycle length, follicular dynamics, follicular waves, dominant follicle