Characterization of follicular dynamics in the Kenyan Boran cow

Abstract

Follicular dynamics is one of the most important subjects in ovarian physiology. In cows and heifers, it is characterized by waves of follicular growth and regression. This has been largely studied in European breeds while studies on Zebu cattle ( Bos indicus ) are limited. Differences between breeds of cattle exist and this information has been used to establish correct ovulation parameters and management procedures for these breeds. This study aimed at investigating the follicular dynamics of the Kenyan Boran cow ( Bos indicus ) during its estrous cycle. Follicular developmental characteristics were evaluated using a 5.0-7.5 Megahertz (MHz) linear array portable ultrasound device. Transrectal scanning was done daily for a period of two consecutive estrous cycles in 15 Boran Cows. Predominantly, the cows exhibited three (70.59%) follicular waves per cycles while a smaller population of the cows (25.53%) exhibited two follicular waves per cycle. Of the animals used, (5.88%) had four follicular waves per cycle. The pre-ovulatory dominant follicle size for the Kenyan Boran cow was recorded as 13.56±1.73 mm and was higher than the diameter of all the other dominant follicles. The duration of dominance of wave one was approximately three days longer and the onset of atresia of the first wave occurred approximately two days later in two-wave cycle animals than in three-wave cycle animals (P<0.05). There was no significant difference in cows with different waves per cycle. This study observed that like in other Boran breeds the follicular dynamics in the Kenyan Boran cow are characterized by a higher incidence of cycles that have three follicular waves associated with a short persistence of the dominant follicle of the first wave.