Having had two horses that had
"heaves", aka Emphysema, I understand what is being said below. The exhale
is also called "double expiration." One of my favorite horses developed
this around the age of 27, for what reason I have no idea. I gave him
Ventro-pulmin on the advice of our vet, but it did not help enough. Poor
old horse, he could just barely walk up an easy slope to his shelter for his
hay. Time came when I figured he needed release from this misery and I
had him euthanized. Our youngest daughter's childhood horse, a very
dear QH, developed it when he was about 13, but feeding him pellets instead of
hay kept him functional for many years, and I think he was put down due to old
age after a second career of being a kids' learning horse. Kids used to
climb on him, under him, over him, slide off his rump; he adored
children.
It's the visible line at the junction of the tendinous
and muscular parts of one of the abdominal muscles (external abdominal
oblique), caused by hypertrophy (increase in size) of the muscle fibers. This,
and other abdominal muscles are used in the "abdominal press" to move things
into and out of the abdomen, and sometimes as in this case out of the thorax.
It's caused by a condition called COPD (Chronic
Obstructive Pulmonary Disease), or just "Heaves". These horses lose lung
compliance, and in order to still satisfy oxygen needs, breathe at higher lung
volumes than normal. Due to the decease in lung compliance, expiration is no
longer a passive process, and they have to use abdominal press to expire, and
so you see an increase in size of this muscle.
Just had a test on this material, figured i'd share.
:-)
