around 36 h post-administration. Dose is usually 2500-3000 IU administered
i.v. hCG is reliable and effective for inducing ovulation in mares receiving the
hormone for the first 1-2 times in a year. However, the response can become
less reliable (i.e. the mare may not ovulate within the predicted interval) if
mares are treated repeatedly during the same breeding season and some
individuals (particularly older mares) fail to respond to hCG; if a mare fails to
respond to hCG given at the appropriate stage of follicle development, it is
advisable to switch to a GnRH agonist for future ovulation induction attempts
Equine Follicle Stimulating Hormone (eFSH)
A purified equine pituitary FSH product (eFSH; Bioniche Animal Health USA)
was previously available for inducing superovulation in mares (McCue et al,
2007). The recommended regime was 12.5 mg eFSH twice daily i.m. from 5-7
days after ovulation, combined with induction of luteolysis. hCG or deslorelin
are used to synchronize the ovulations. eFSH has also been used to advance
the first ovulation of the year in transitional phase mares. However, this
product was removed from the market some time ago. More recently,
research studies have described the efficacy of a recombinant eFSH product
for both simulating superovulation (Meyers-Brown et al 2011) and inducing
early season cyclicity in mares, although the product (and a related
recombinant eLH that can be used to induce ovulatin) have not yet been
produced for commercial use.
Progestins
The most commonly used exogenous progestin in horses in altrenogest
(Regumate ). Uses include suppression of oestrous behaviour, shortening the
spring transitional phase, oestrous synchronization, maintenance of
pregnancy and maintaining uterine quiescence in high risk pregnancies.
Natural progesterone-in-oil (50 mg/ml) is available but needs to be
administered i.m. daily; 100-150 mg is sufficient to suppress oestrus, >200 mg
per day is required to maintain pregnancy.
Inadequate luteal progesterone production has been proposed to contribute to
early embryonic loss in mares, but ‘progesterone insufficiency’ is a controversial
topic. Progesterone levels > 4 ng/ml are considered sufficient to maintain
pregnancy. Progesterone supplementation is usually initiated either a few days
after ovulation, following ultrasonographic diagnosis of pregnancy (i.e. day 14),
or following an event that may compromise luteal survival. Supplementation is
continued until day 100-120 of gestation, when placental progesterone
production is sufficient to maintain pregnancy.
Other synthetic progestins, such as medroxyprogesterone acetate (DepoProvera®), hydroxyprogesterone caproate (Hyproval®), norgestomet (SynchroMate B®) and megesterol acetate (Ovaban®) do not reliably suppress oestrus
or support pregnancy in mares. However, long acting progesterone and
altrenogest products able to support pregnancy for periods of 7-14 days have
been produced in North and South America and used to successfully support
pregnancy in non-cycling embryo transfer receipient mares pre-treated with
oestradiol preparations.
®
15-‐18
February
2016
East
London
Convention
Centre,
East
London,
South
Africa
84