Effect of follicle size and cumulus oocyte complex grade on in vitro embryo developmental competence for boran cows
Zebu cattle are the predominant cattle breed in the arid and semi arid lands (ASAL) of Kenya. The Boran, a zebu is one such breed whose full utilization is yet to be optimized as it has been viewed as a low grade animal. This is in spite of its adaptive superiority to the ASAL's. A feasible, practical and economic plan for utility of this breed is to produce its 1st filial generations (FI) cross-bred animals adapted for various production systems. This study sought to utilize a combination of emerging reproductive technologies, especially the in vitro embryo production (IVEP), to explore the potential of constant production of F 1 embryos for delivery of the desired FIs. Such innovations would enhance the utility of the indigenous cattle breeds such as the Kenyan Boran beyond beef production. This study embarked on research to understand how the follicle size and oocyte grade quality would influence blastocyst output in an IVEP system. Thus, the association between the follicle size and the grade of the cumulus oocytes complex (COC) was evaluated. In addition the extent to which these factors affected blastocyst development was studied. Brilliant Cresyl Blue (BCB) stain was used to evaluate competence of the COC's while rates of in vitro maturation, cleavage and blastocyst formation were used to determine parameters of the IVEP process. Some 308 ovaries collected from 154 Boran cows at slaughter from local abattoirs were utilized for the study. Follicles were evaluated and divided into 3 groups: - group 1: 1-3 mm, group 2; 3-6 mm and group 3; > 6 mm in diameter. The total numbers of grade A and B cac's aspirated from each of follicle group sizes graded and were recorded and used for IVEP process. The IVEP process involved in vitro maturation (22-24hrs), in vitro fertilization (18-22hrs) and in vitro embryo culture (7days). The cac's were fertilized with pre-tested semen from a proven bull and the resulting zygotes cultured to the blastocyst stage. Cleavage and blastocyst rates were assessed 72 hrs post-fertilization and 7 day post-culture, respectively. Some 2658 oocytes were aspirated, 1628 cac were ran through the IVEP process while BCB stain test was conducted on 1030 oocytes. This thesis reports maturation, cleavage and blastocyst rates of 90.95%, 60.48% and 27.55% respectively, for cacs from Boran cows during the IVEP process. There was no relationship between the follicle size and the grade of cac aspirated (P> 0.05). It was shown that both grade A and grade B cac's can be used for IVEP process for the Boran. There was also no relationship (P> 0.05) between the follicle size, cac grade and the rate of maturation However there was a strong relationship (P<0.05) between the follicle size, cac grade and cleavage rate and blastocyst formation. The follicle size and grade significantly influenced the BCB competence rate, (P<0.05) with caC's from group 3 being the most competent (88.33 %) followed by those from group 2 (77.33%) and then those from group 1 being the least (73.09%). The study revealed that in the Boran it was possible to obtain blastocyst from COCOs aspirated from all follicle size groups, although more would be significantly obtained from COC's from follicles larger than 3 mm in diameter. This study shows that in vitro production of embryos for the Boran cow in Kenya is technically feasible and that the Boran would be a good cow for ova harvesting. Unlike the Bos taurus, in the Boran, follicles as small has 1-3 mm can be utilized for IVEP processes. By the time the follicle size is about 6 mm in this species, the oocytes competence is fully attained. Therefore in the Boran follicles as small as 1mm can be utilized in ovum pick up sessions. This study has set up baseline information for enhanced utilization of the Boran cow as oocyte donors.