important than dose, and 7–8 mL of a 2% lidocaine solution is sufficient to
block the perineal region of a 500 kg horse.
Morphine does not affect the nerve conduction responsible for skeletal
muscle motor control, and thus will not cause recumbency. In other words
it provides perineal and hindlimb analgesia but not anaesthesia
Epidural administration of alpha2 agonists provides analgesia of longer
duration than systemic doses. These drugs do not give a complete
sensory block at clinical doses. High doses can block all types of fiber,
causing
ataxia/paresis.
Systemic
effects
(sedation,
hypertension/hypotension, bradycardia) are common.
An epidural block typically takes 15 minutes to develop. Volumes <10 ml
can be injected in less than a minute. Volumes >10 ml should be injected
slowly (5–10 min), due to mechanical compression of nerve endings in the
epidural space resulting recumbency.
Motor blockade (e.g. ataxia, recumbency) may be caused by local
anesthetics and α2 agonists (high doses). Ataxia and weakness may not
be evident while the horse is standing in the stocks, so it is essential to
evaluate the horse before attempting to move it! If a satisfactory response
to an epidural block is not obtained after the appropriate time, it may be
best to delay surgery for a few hours or elect general anaesthesia.
Repeatedly topping up an epidural that “is not working” runs a high risk of
inducing recumbency and panic in the horse if the accumulated dose
starts to take effect.
Horses which become unexpectedly recumbent in this manner may panic
and make frenzied attempts to st and, posing a danger to themselves and
handlers. In case of recumbency, sedation or even general anaesthesia
may be necessary to maintain the horse in this position until motor
function is regained. Where feasible, moving the horse to a padded
induction room is the safest option for recovery.
Don’t tie weights to a retained placenta
Retained placenta is reported to be the most common postpartum
problem in the mare. The most obvious sign of a mare with retained
fetal membranes is the appearance of tissue protruding from the vulva.
There is a reported higher incidence after dystocia, prolonged
gestation, Caesarian section and placentitis. Mares over 15 years old
have a significantly higher incidence of retained placenta than younger
mares. Mares that have had retained placentas before demonstrated a
3 x greater probability of having retained placenta after foaling than
mares without this history. A possible reason for this increase is that
formation of pathological adherences between the endometrium and
chorion during the first retention of the placenta may recur at
subsequent pregnancies. Mares that develop uterine or systemic
15-‐18
February
2016
East
London
Convention
Centre,
East
London,
South
Africa
79