Human chorionic gonadotropin (hCG) in cow acts in a
similar way to LH. Effectively, hCG induces ovulation and
has a direct luteinizing effect on ovarian cells, extends the
life span of the CL, and increases endogenous progesterone
(P4) synthesis by the CL [104–106].
The use of hCG in an Ovsynch-based protocol has some
advantages over GnRH: luteolysis is not delayed nor is the
length of the estrous cycle prolonged [106]. A delayed interval
between ovulation and insemination can be a main
factor affecting fertility during the warm season [96]. Thus,
replacing GnRH with hCG during periods of HS seems
appropriate. Cows under summer HS in an Ovsynch program
given hCG instead of GnRH showed an improved
cumulative pregnancy rate on Day 120 postpartum [107].
The administration of hCG after AI seems to improve
conception rates under HS. Shabankareh et al. [108] reported
a higher pregnancy rate during the warm period for
hCG-treated cows at 5 days after AI versus saline-treated
cows.
Equine chorionic gonadotropin (eCG) has long-lasting
LH and FSH-like effects that stimulate estradiol and P4
secretion [109]. Thus, eCG administration in dairy cattle
results in the recruitment of more small follicles showing
an elevated growth rate, the sustained growth of medium
and large follicles, and improved development of the
dominant and preovulatory follicle. In consequence, the
quality of the ensuing CL is improved, and thereby P4
secretion increased [109]. On the basis of these characteristics,
eCG treatment is used in veterinary medicine to
control the reproductive activity of the cow. Results indicate
that eCG administration after the use of a P4 device
may increase the synchrony of ovulation and improve the
conception rate in FTAI protocols. The positive effects of