46TH
ANNUAL
CONGRESS
OF
THE
SAEVA
SKUKUZA
16-‐20
FEBRUARY
2014
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response has been reported, as have significant injection site reactions in older
mares.
Study 1: The use of a GnRH vaccine to suppress mare ovarian
activity in a large group of mares under field conditions
Botha, AE, Schulman, ML, Bertschinger, HJ, Guthrie, AJ, Annandale, HC and Hughes, SB
(2008) Wildlife Research 35, 548-554
Aims: This study investigated the effects of active immunisation against GnRH on
reproductive cyclicity in a large group of mares of different age categories and
monitored the effect of vaccination and mare age on injection-site reactions.
Methods: A total of 65 mares of various breeds, between 3-17 years of age were
assigned to either a control (n = 10) or an experimental (n = 55) group. Within the
experimental group, mares were subdivided into one of three age categories:
Category 1 (<4 years, n = 26), Category 2 (5–10 years old, n = 18), and Category 3
(>11 years). On D0, all experimental mares were injected intramuscularly into the
left gluteus muscle with 2 mL (400 µg) of the GnRH-vaccine (Improvac®, Zoetis,
South Africa), and all mares from the control group received 2 mL of a sterile saline
solution. On D35, a booster vaccination was similarly administered. Mares were
observed daily for one week after the vaccinations for injection-site reactions. The
ovaries and reproductive tracts of each mare were examined by means of rectal
palpation and ultrasonography on days 0, 35 and 70. Blood was collected weekly for
determination of serum progesterone concentration (SPC) until D175.
Results and discussion: On D35 after primary vaccination all of the control
mares and 14.5% of the experimental mares showed evidence of ovarian activity; and
on D70, all control mares and none of the experimental mares showed evidence of
cyclic activity. No age-related effect within treatment groups was found. The few
animals displaying injections site reactions were observed only after the booster
vaccination. All adverse reactions were found to be transient and mild, and
unapparent by day 6. The SPC measurements indicated that all experimental mares
remained in anoestrus until the end of the observation period D 175.
Study 2: Reversibility of the effects of GnRH vaccination used to
suppress reproductive function in mares
Schulman, ML, Botha, AE, Muenscher, SB, Annandale, H, Guthrie, HJ and Bertschinger, HJ
(2013) Equine Veterinary Journal 45, 111-113
Aims: This study investigated the previously incompletely defined reversibility and
duration of anoestrus induced after immunisation with a GnRH-vaccine in a group of
mares over a period of approximately two years.
Methods: The mares (n=51), aged between 3-17 years, and either Thoroughbred
or similar light-horse type, were subdivided into three age categories: Category 1
(<4 years, n = 25), Category 2 (5-10 years, n = 16) and Category 3 (>11 years, n =
10). The mares all showed evidence of cyclic reproductive activity on clinical
examination and were vaccinated twice (with a 35 d interval) with 400 µg of the
GnRH-vaccine GnRH-vaccine (Improvac®, Zoetis, South Africa). By D70, all mares
showed anoestrus on both clinical examination and blood samples for SPC by radioimmune assay (SPC <1 nmol/l). Mares were monitored via blood samples for SPC
until D720 after initial vaccination for both SPC and anti-GnRH-antibody titre by
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