76
46TH
ANNUAL
CONGRESS
OF
THE
SAEVA
SKUKUZA
16-‐20
FEBRUARY
2014
enzyme immuno-assay. Samples were collected until individuals resumed cyclic
ovarian activity, defined by SPC >6 nmol/l, the upper threshold concentration for
winter anoestrus.
Results and discussion: By D720, 92.2% of mares had resumed cyclic activity
with a mean interval of 417.8 d (SD+23.9; range 232-488 d; median 344 d). A
significant age effect (P=0.028) was seen, with the youngest (<4 years) showing a
longer interval to reversibility than the oldest (>11 years) age category. The mean
GnRH-antibody titres although not significantly different, were higher in the youngest
compared with the oldest mares. The study demonstrated a variable reversal of
anoestrus in most mares immunised with Improvac®. A significantly earlier
resumption of cyclic ovarian activity was observed in the oldest compared with the
youngest mares.
Study 3: The effects of GnRH-vaccination in reducing post-surgical
castration complications carried out under field conditions in colts
Aims: The administration of a commercially available porcine GnRH-vaccine
(Improvac®, Zoetis, South Africa) to colts followed by a booster after a 30 day
interval will effectively decrease testicular dimensions and vascular flow to the testes.
These effects will reduce the risks associated with surgical castration, decrease stress
and improve post-operative growth.
Methods: Intact colts (n=22) of various horse breeds aged between 15-18 months
of age were included in the study. The 22 colts were randomly divided into the
following groups: Group 1 (n=7) were vaccinated twice with 2 ml of Improvac® on
D0 and D35 and then surgically castrated on D60; Group 2 (n=6) were vaccinated
twice with 2 ml of Improvac® on D0 and D35 and then surgically castrated on D90;
Group 3 (n=6) injected twice with 2 ml sterile 0.9% NaCl on D0 and D35 and then
surgically castrated on D60; and Group 4 (n=3) negative controls injected twice with
2 ml sterile 0.9% NaCl on D0 and D35 and no castration. Castrations took place
under field conditions and all colts were placed u nder general anaesthetic and placed
in the right lateral recumbent position. An open surgical technique was used and the
wounds were allowed to heal by second intention healing. All colts were monitored
daily for 10 d post-surgery for clinical signs of post-operative complications: vital
signs, habitus and observation of the surgical site for post-operative swelling and
discharges.
Measurements: a) The length, width and height of both testes (if still present)
were measured on D1, 35, 60 and 90. Post-castration, excised testes were examined
macroscopically and length, width and height and testicular mass with and without
adnexa (epididymis) were recorded and the testicular volume was calculated.
Histological samples were prepared for microscopic determination of spermatogenic
activity and vascular characteristics.
b) Blood samples for serum testosterone determination by radio-immunoassay were
collected: (i) 6 days prior to, on the day of and for the two days following
vaccinations and (ii) 6 days before, on the day of and for 21 days post-castration.
c) Faecal samples for faecal glucocorticoid metabolite (FGM) measurements by
radioimmunoassay as a measure of physiological stress associated with surgical
castration and post-operative recovery were obtained from all colts.
d) Growth rates of the colts were measured on D0, D180 and D 360 using a
combination of: wither height, girth measurement, body weight and a monthly
radiographic lateral view of the right cannon bone.
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