Actually, the only common denominator between the species is the depression
in prolactin secretion. You don't see the reproductive problems in cattle
that you do in horses, possibly because the progesterone and estrogen profiles
during pregnancy are the exact opposite from a horse--so depressing progesterone
and increasing estrogen probably wouldn't have as big of an effect. We
know that ergot alkaloids can cross a ruminant placenta and reach the fetus, but
to my knowledge the steroids are not influenced by the fetus in ruminants like
estrogen is in horses. The cattle physiologists insist that horses do
everything backwards, and they may be right.
As for the milk production and udder development issues, we don't see those
in cattle either--they have a backup hormone called placental lactogen (produced
by the placenta), which works like prolactin, so even if prolactin is reduced in
a pregnant cow, she'll still develop an udder and start the initial process for
secreting milk prepartum.
The biggest problems in cattle are divided into 3 groups--summer syndrome,
fescue foot, and fat necrosis. Summer syndrome is characterized by
elevated body temperatures, reduced feed intake, weight loss, and altered
grazing behaviors, and from what we know of feedlot performance, it takes steers
a while to recover (sometimes up to 2 months) once they are removed from
infested pasture. Fescue foot is seen in colder months, and this is what's
similar to ergotism--we see a dry gangrene of the extremities. (Traditional
forms of gangrene weep). They often lose the tips of their ears and tails,
and in severe cases they slough their hooves (much like you see in chronic
selenium toxicity). The reason for both problems is that the alkaloids
constrict the veins in the ears, tail, and legs, so adequate blood circulation
is lost--keeping the blood in the core of the body raises the body temp in the
summer, and in the winter the cold makes the problem worse. Cattle can't
sweat to decrease body temp like a horse can, so we don't see the temp-related
problems in horses that we see in cattle.
Fat necrosis is an odd duck. It's more likely to turn up in brood
cows, and instead of being a traditional necrosis (rotting tissue), the fat
contains a higher mineral content that normal. As a result, it's like
hardening of the arteries, the fat tissue loses it's "give", and can create
problems with digesta passing through the gut or with a fetus being
delivered.
(Can't tell this stuff is ingrained in my brain, can you? LOL)
Lisa
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