Winter coat retention
I haven't posted for a while since my horse has been "stabilized" with
pergolide and proper diet. Now that Spring is here, I am concerned that
she is not shedding. My other horse is losing her coat dramatically! I
have read that a reduction in pergolide dose seems to help the coat
thickness problems. I wouldn't mind the thick coat but she seems hot
now and the temperatures are not even very high yet. When they get
higher, she will melt!
Her ACTH had gone from 132 in Nov to 24.5 in Feb. Her attitude and
general demeanor were greatly improved, as well. Is it correct that
ACTH levels drop from Spring into Fall?
I'd appreciate any input if someone has the opportunity.
Eleanor Kellon, VMD
--- In EquineCushings@..., "horsecorrect"
Now that Spring is here, I am concerned that
she is not shedding. My other horse is losing her coatdramatically! I
have read that a reduction in pergolide dose seems to help the coatWhat we know about shedding so far is (this is normal horses):
- early spring is the only time the pituitary is sensitive to
melatonin, the hormone that is released during darkness.
- beginning sometime in February to April (some individual
differences), prolactin levels in the pituitary begin to rise
- decreasing melatonin levels in the spring may trigger a surge of
prolactin, or change the sensitivity of the target cells to
prolactin, which in turn causes both shedding and resumption of
- ACTH levels are elevated in September, may still be elevated in
January, are low in May
What we don't know is what, if anything, happens to ACTH during the
spring transition period. Like ACTH and the other POMC derived
pituitary hormones, Prolactin secretion is suppressed by dopamine.
Blocking dopamine (dopamine inhibition) also releases the block on
ovarian activity in the winter so, conversely, dopamine also
suppresses ovarian activity.
We know that Cushing's and the elevated ACTH and prolactin (? some, ?
all) that goes along with it is caused by loss of dopaminergic
hormones. So far so good. Where the connection gets shakey is that
you then would predict the horse would shed. I don't think we have a
very good handle on why they don't.
Some/most horses shed on pergolide, some don't. Some even
paradoxically grow a longer coat. That latter group may be horses
that really didn't need it, since increasing dopamine activity and
suppressing prolactin release would be expected to mimic the fall and
cause a longer hair coat to grow.
If this seems rambling, it is - because I'm not sure there's an
answer to the questions. My "best guess" would be that the ones that
are not shedding may have oversuppression of the seasonal prolactin
rise that normally triggers shedding. If that's the case, lowering
the pergolide dose (after making sure ACTH is indeed controlled)
might indeed trigger shedding.
That doesn't really explain why Cushing's horses have long coats in
the first place though. If prolactin rises along with the pituitary
hormones (and we know it does at least in some mares), why don't they
shed instead of growing a long coat? Maybe they become insensitive to
Prolactin by having constantly high levels.
At 1:32 PM +0000 3/25/08, Eleanor wrote:
Blocking dopamine (dopamine inhibition) also releases the block on ovarian activity in the winter so, conversely, dopamine also suppresses ovarian activity.This is interesting, because last summer, Penny had very subtle heats, not like every year previous to getting pergolide, when she was a sex maniac when she came into heat. I guessed that the change was because of some aspect of her treatment: pergolide, Thyro-L, or diet and nutrition.
I wonder if pergolide might make a mare less fertile, not that I want to breed Penny. Does how overt heat seems to be relate to fertility? In Penny's case, it seems she'd be less willing to breed, but if she was bred, would it be harder for her to conceive?
I guess it doesn't really matter, except if it affects Penny's general health in some way.
Penny is shedding a lot, so that issue doesn't seem to be a problem for her. She's still got lots of hair to go yet, but it's coming out in heaps, though maybe a bit less than last spring. Then again, this winter, I think she wasn't as shaggy as last winter.
Eleanor Kellon, VMD
--- In EquineCushings@..., Sandra Su <ssu@...> wrote:
I wonder if pergolide might make a mare less fertile, notIntensity of estrus isn't related to fertility. The ladylike mares are
just as fertile as the shameless ones! In the case of a mare with
Cushing's, the normalization of hormones would tend to make them more