|Glacier Creek Stable is a riding
stable operating as a concession in Rocky Mountain National
Park, outside of Estes Park, Colorado. The stable is allowed
up to 80 horses by the National Park Service. The company,
Hi Country Stables, has always mixed mares and geldings
in the horse herd there. Many horse operations do not like
to mix the sexes because of fighting and injuries that may
result. Some owners prefer geldings because they believe
them to be more even tempered. The management at Glacier
Creek Stable has found, over the last 10 summer seasons,
that, although there may be some behavior problems associated
with mares, that mares are the majority of their most athletic
long distance horses. Because of the athletic ability and
durability of the mares, the management would like to eliminate
problems associated with mixing the sexes.
To this end,
they tried an interesting experiment during the summer of
This is strictly an anecdotal
experiment on a small band of mares. For advice on
your own horses, please contact your local veterinarian.
Newer commercial equine preparations may achieve similar
results. This article is intended only as a suggestion
that extraneous behavior in mares may be suppressed by pharmaceutical
On June 5, 1997, at the beginning
of their busy summer season, the Hi Country company veterinarian
implanted 24 stable mares with a progesterone implant. He
did three more on June 7th and a final two on July 14th
for a total of 29 mares. Another company stable had another
veterinarian implant about 10 mares the previous summer,
and although not as carefully documented, the people in
charge of the horses said they would implant all the mares
again if the opportunity arose. Another local stable had
about 4 of their mares implanted in 1997 and reportedly
were happy with the results.
Patrick McCue from Colorado State University conferred with
the local veterinarian on optimum dosages. Dr. McCue works
with a product called Synovex S which has been used as a
growth hormone for beef steers. He tested doses of 8, 32,
and 80 implant pellets. All mares still had standing heats.
Sixteen pellets, however, is the usual dose and may control
some unwanted behavior, but is not heat suppressive. Sixteen
pellets of Synovex S releases only 3 mgm. per day of progesterone.
50 to 100 mgm. are needed to suppress heat. Other products
available did not seem to do the wanted job well or at a
reasonable cost. Regumate was the only sure way to suppress
heat. Regumate comes in a syrup form and is given orally
on a daily basis. It is also quite expensive for a 21 day
cycle. The mare will come into heat immediately when the
Regumate treatment is discontinued. It is used by breeding
farms to help settle mares for breeding. Progesterone injections
are also expensive and are not tolerated well by the mares.
The drugs DepoProvera, Norgestamate, and Synchromate B,
that are used to synchronize breeding cycles in beef cattle,
did not work as desired.
The Hi Country veterinarian followed
a 3-step procedure for implanting the mares, treating up
to five head in a group.
1. The mare was injected intravenously
with 1.5cc. of Rompun as a sedative.
2. When the mare exhibited the maximum
sleepy state from the sedative, the area of the implant
was deadened with injections of Procaine.
3. A special injection gun with an
8 gauge needle was used to insert two doses of eight progesterone
pellets subcutaneously in the front of the right pectoral
muscle on each animal. The second dose was placed about
a half inch away from the first, using the same entrance
The Hi Country veterinarian stated
that, although the dosage will not stop the heat cycle in
the mares, the aberrant behavior exhibited during heat in
many mares should be reduced or eliminated in up to 80%
of the animals. He stated the effects should be visible
within a few days and should continue for approximately
The vet made follow-up visits the
next day, and the third day to assess any swelling of the
brisket. Some swelling was visible in most of the mares,
but none were unusual and all were back to normal size within
a week. One mare had been seemingly unaffected by the Rompun
sedative. She was given a second Rompun injection and still
had to be restrained with a leg hobble and twitch. She was
sore for about three days from fighting the restraints.
Only one other mare required any restraint and she was leg
hobbled. She did not fight the hobble.
Definite improvement was noticed
in at least 10 of the mares. Mares that were "kickers"
and not able to be used on trail rides except as guide horses
or at the end of a line, were much better behaved and could
be used as needed in the line. Five of the treated mares
were shipped from the stable before the end of the summer.
One was shipped due to chronic colic, but she had been noticeably
improved in her behavior. One was shipped for chronically
lying down on rides. And three were shipped out for kicking
and behavior problems that had not been significantly improved
by the implants. The three with behavior problems were new
to this horse herd and had not established themselves well
in the herd pecking order. The balance of the mares were
all well behaved, but may have been that way anyway.
Ten of those had been with this horse herd for years and
were usually problem free. Five were new to the herd but
had no major problems with the other horses. Fewer bites
and kicks were observed than in previous seasons. The horse
herd seemed much quieter at night and during the day. Attention
to mares in heat by the proud-cut geldings was almost non-existent.
In the opinion of the Hi Country Stable management at that
time, the procedure had been a success and they would not
hesitate to repeat it again another time.