Necropsy Report
Date:                          1/1/10
Prepared by:           Albert Kane, DVM, MPVM, PhD
Location/Event:      Calico Complex Gather
Animal ID:           6 month old, dark bay/brown, colt
History:  The pilot reported this colt lied down twice while moving just ½
mile from the original location of the band of horses. The second time he
radioed to the trap for wranglers to come with a trailer and assist the
colt as he seemed unlikely to make it to the trap. I accompanied the
wranglers to the location. We arrived to the colt’s location about 10
minutes after the call from the pilot. On arrival he was found dead, lying
in left lateral recumbency, with no signs of struggle or agonal movements
apparent in the surrounding snow.
Examination: Alan Shepherd accompanied me during this necropsy examination.
The carcass was rolled onto the right side, no external abnormalities were
noted. Front right leg was lifted and reflected dorsally. On opening the
chest cavity negative pressure was apparent. There was no blood present in
the trachea. There was a large amount of free blood in the chest cavity.
The lungs were pink and airy with no abnormalities noted.
On examination in-situ a hole was apparent in the pulmonary artery at the
base. The left ventricle was thickened and larger than expected and the
atria were thin and without muscular tone. There was an area of thinning
and apparent aneurysm on the left atrium.
The abdominal cavity was examined with no abnormalities noted. Body
condition was moderately thin with only small amounts of subcutaneous and
abdominal fat noted.
Conclusion/Differentials/Dx: Left side heart failure.
Death caused by acute pulmonary artery rupture attributable to a
pre-existing, probably congenital heart condition.
Gather related but attributable to a pre-existing condition
Albert J. Kane, DVM, MPVM, PhD
Veterinary Epidemiologist
Senior Staff Veterinarian
APHIS/BLM Wild Horse and Burro Partnership
- - -
(Comments added by Tracie L. Thompson)
Basically, the foal died from Acute Pulmonary Aneurysm Secondary to Left Ventricular
Hypertrophy. This condition is genetic, is a pulmonary condition, and is a congenital
heart defect. So, based on this report’s information, the answers to the questions above…
Was this foal’s death a direct result of the gather? Yes, if this foal was not
being gathered, he would not have died at that time.
Could this foal’s death have been prevented? No, this foal’s death was imminent.
It is likely that the foal was in pain daily until his death, suffering from symptoms
such as shortness of breath, fatigue, nutritional deficiencies, just to name a few. It
is highly unusual for foals with this condition to live past the age of 6 months age and
in some cases even 1 month of age without medical and/or surgical intervention.
What were the actual circumstances? The only information that is available at this
time as to the actual circumstances of this foal’s death from an official accounting is
the necropsy report above. Other reports have not become available at the time of this
writing. As mentioned above, there are several second and third party reports available
on the internet.
The BLM states that it is common to have injury, illness and sometimes death during gather
operations. They state however, the rate is very low.. According to some sources, the rate
is as low as 1%. Other sources place the rate much higher.
There is also protocol for the pilot to follow should he see a horse not able to keep up
with the movement of the herd. If the pilot observes such a situation, he is to radio the
gather officials to request assistance for the horse, and he is to reduce his pursuit of
the horse and/or cease his pursuit of the horse. This is to ensure that the horse is not
pushed beyond his physical limitations. According to the necropsy report above and sources
within the BLM, this was the case during the development of this situation.
- - -
We asked Corrine Davis, DVM, PHD, a retired university veterinary pathologist, wild horse
advocate and an adopter of a several wild horses (and a burro) to review the necropsy
report.  Her comments are as follows.
This exam as described could easily be carried out in the field. The chest being full
of blood and the finding of a ruptured pulmonary artery are consistent and could easily
explain acute death.  The exact nature of the heart defect was not described. The
ventricular hyperplasia and dilated atria could have been secondary to a primary heart
defect.  The usual congenital defects are either septal defects (holes), malpositioning
of great vessels, or failure of fetal structures to close. I saw no estimate of weight of
the animal.  I think the conclusions are valid and that the cause of death was due to
rupture of an aneurysm in a great vessel.
Cardiac defects are relatively common congenital defects in many species including man.
- - -
(Additional information provided by Tracie L. Thompson) 
The following are links to educational sites if you would like to learn more about this condition:
The Merck Vet Manual, Heart Failure
Answers to Equine Cardiology Practice Problems: LAMS 5313 Dr. Barton, Case Studies
UC Davis, Center for Equine Health, The Equine Heart