A Study Of Follicular Dynamics In The Kenyan Boran Cow
Although ovarian follicular dynamics has been documented in some Zebu cows, literature on the same for the Boran cow is scarce. The current study aimed at providing this information so as to optimize capacity of this breed through utilization of some assisted reproductive technologies like estrous synchronization, in-vitro embryo production and embryo transfer. Follicular development characteristics during estrous cycle were evaluated using a 5.0-7.5 Megahertz linear array portable ultrasound device from 15 randomly selected cows that were open but cycling and of a 2-2.5body condition score. The cows were induced into estrous using 500μg (2ml) of Cloprostenol (Estroplan®). Daily scanning of the ovaries was done and the follicles counted, measured for diameter and recorded. These activities were carried out daily for two inter-estrous cycle lengths. Also the location of the three largest follicles and the corpus luteum were sketched for each ovary on a daily basis. The three sketched follicles were used to track and evaluate for daily follicular dynamics. Follicular parameters such as follicle numbers and sizes were utilized to determine wave emergence, selection and deviation, dominance and atresia characteristics that constituted the dynamics. Changes in the size and growth of corpus luteum were also tracked. The cows exhibited two, three and four follicular waves during the estrous cycles. Most of the cows (66.67%) exhibited the three wave cycles, while 26.67% had the two wave cycles and 6.67% had the four wave cycles. The pre-ovulatory follicle attained a mean maximum diameter of13.56 ± 1.73 millimeters, which was significantly (P≤0.05) higher than the diameter of all the other dominant follicles. Cows with two wave cycles had an estrous cycle length of about 18 days while those with three and four wave cycles had extended estrous cycle lengths of about 25 days. In the cows with fewer wave cycles, the duration of dominance phase of first wave was approximately three days longer than their 3-wave and 4-wave counterparts. There was no significant difference in both the growth and atresia rates for dominant and subordinate follicles among waves within the estrous cycles. Although there was no significant difference in maximum diameter of the dominant follicle between the first and the second wave in cows exhibiting the two wave cycles, three-wave and four-wave cycle diameters of the d o m i n a n t f o l l i c l e of the ovulatory wave was significantly larger than those o f the other waves. There was no significant difference indiameter of corpus luteum noted among the cows. The corpus luteum from four wave cyclespersisted the longest period. It was concluded that the follicular dynamics of Boran cow compares well with other Zebu breeds studied so far and three ovum pick up sessions can be done for utilization of this breed in in-vitro Embryo Production and Embryo Transfer.