Authors : Tilaye Demissie, Tefera Yilma, Tamrat Degefa, Adise Ambilo, Tsigereda Tadesse and Alemayehu Lema
Abstract: Cattle breed, climate in which cattle reared and management result in differences in ovulation time and responses to reproductive hormones. Most of the data on ovulation synchronization and conception rate to timed AI in cattle of Bos indicus and their cross to Bos taurus were from humid tropical countries. Little has been known from tropical hot African countries. The study aimed to evaluate the effect on pregnancy rate when progesterone is added to or when initial GnRH is removed from the usual ovulation synchronization that uses GnRH- PGF2α- GnRH combination. To achieve the objective, cross breed dairy heifers (n = 91) were randomly grouped into 3 groups. Group 1, heifers received 100 μg GnRH on day of start (D0), 500 μg PGF2α on day 7 and 100μg of GnRH on day 9. Group 2 heifers were treated as group1 but heifers received progesterone as Controlled Internal Drug Release (CIDR). Group 3 heifers were treated as in group 2 but without D0 GnRH. All inseminations were made at 19h of the 2nd GnRH. Transrectal ultrasonography was used to assess ovarian changes and pregnancy. Group with D0 GnRH had significantly higher (p<0.05) ovulation 48h after D0 GnRH (28.6% in Ovsynch and 12.5% in CIDR+Ovsynch) and significantly higher new corpus luteum at D7. Pregnancy rate was significantly higher (p<0.05) in group with CIDR Ovsynch (56.3%) than without CIDR (39.3%). The mean diameter of larger follicle at first standing, the mean diameter of ovulatory follicle and that of corpus luteum were not affected (p>0.05) treatment protocol. In conclusion, in Bos indicus X Bos taurus reared in hot dry climate both CIDR insert and D0 GnRH improved pregnancy rate to timed artificial insemination and recommended.
Tilaye Demissie, Tefera Yilma, Tamrat Degefa, Adise Ambilo, Tsigereda Tadesse and Alemayehu Lema, 2021. Pregnancy Rate of Cross Breed Dairy Heifers Subjected to Ovulation Synchronization and Fixed Time Artificial Insemination. Journal of Animal and Veterinary Advances, 20: 86-90.