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. Key words: Boran, estrous cycle length, follicular dynamics, follicular waves, dominant follicle.
Highlights
A higher (P=0.002) proportion of Boran cows (100%) exhibited two follicular waves per estrous cycle than B×H crossbreds (56%)
Our study revealed the same is true with purebred Boran and crossbred B×H cows raised in Ethiopia, even though cows in our study had a longer inter-ovulatory interval (IOI) than Boran cows in Kenya (Muraya, 2013)
The inter-ovulatory interval of the Boran lies in the range reported for other zebu breeds
Summary
The appropriate manifestation of estrus resulting from normal ovarian follicular dynamics is crucial to successful reproductive performance in cattle. A strong understanding of basic reproductive physiology enables appropriate application of controlled reproduction techniques (such as synchronization of estrus, synchronization of ovulation, and embryo transfer). Use of these reproductive biotechnologies can bring about sizeable improvements in the biological and economic efficiency of cattle breeding. Ultrasonography has enhanced the scientific understanding of the basic physiological processes in the estrous cycle including growth and regression of ovarian follicles and ovulation (Zacarias et al, 2015)
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