Tilaye  Demissie, Tefera  Yilma, Tamrat  Degefa, Adise  Ambilo, Tsigereda  Tadesse, Alemayehu  Lema, 
    Pregnancy Rate of Cross Breed Dairy Heifers Subjected to Ovulation Synchronization and
Fixed Time Artificial Insemination,
    Journal of Animal and Veterinary Advances,
    Volume 20,Issue 4,
    2021,
    Pages 86-90,
    ISSN 1680-5593,
    javaa.2021.86.90,
    (https://makhillpublications.co/view-article.php?doi=javaa.2021.86.90)
    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 <i>Bos indicus</i> and their cross to <i>Bos taurus</i> 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- PGF2&#945;-
GnRH combination. To achieve the objective, cross
breed dairy heifers (n = 91) were randomly grouped into
3 groups. Group 1, heifers received 100 &#956;g GnRH on day
of start (D0), 500 &#956;g PGF2&#945; on day 7 and 100&#956;g 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 <i>Bos indicus</i> X <i>Bos taurus</i> reared in hot dry
climate both CIDR insert and D0 GnRH improved
pregnancy rate to timed artificial insemination and
recommended.
    Keywords: Conception rate;Bos indicus;Bos taurus;Estrus;ovulation time