Acetate in low doses in order to produce a cystic
ovarian condition in the mare used during collection.
The mare was fed 0.5 mg of MGA dissolved in alcohol and
soaked into a sugar lump for eight days. At the end of
this time she was showing signs of heat and we were able
to use her for the collecting. This mare showed signs
of going out of oestrus after 5 - 6 weeks and it was
necessary to re-administer MGA for a period of 4 - 5
days. All through the winter however she was used
without a break, in the period when mares are normally
anoestrus, and no further MGA was given until the
return of the breeding season, when she again began to
fall off in sexual activity. Further administration

of MGA soon restored the collecting mares sexual
function. It is also interesting to note that when

the mare's sexual permissiveness waned, then the time
taken for the stallion to mount increased and the
volume and motility of the sample was affected
adversely.

By administering a low dose of MGA it was possible
to supress ovulation but not follicular development and
therefore a condition was produced in the mare which is
paralleled in cystic ovarian disease in the cow. These

cystic follicles remained for a considerable time, and
during the period of anoestrus right round until the
next breeding season, suggesting that the ovaries
remained in this same stage all through the winter,
until a new cycle was triggered off in the spring.

Two conclusions can be drawn from this small
experiment. One is the fact that low doses of MGA
act in the mare rather as they do in the sow where
progestogens seem prone to cause cyst formation
(Narlbandov). Progesterone also has this potential
possibility but to a lesser extent. In a previous
experiment (1965) using Progesterone in Avachis oil
(50 mg per day) it was found that one mare became
cystic to a degree and this persisted to the end of
the breeding season. This effect of progesterone has
also been reported by Loy in California and it would
seem advisable not to use progesterone in the mare at
a low dose level, say 50 mg daily. Pascoe in
Queensland has had greater success using slightly
larger doses of progesterone (around 100 mg per day)
in about 100 cases and it may well be that at this
level follicular development and ovulation are both
supressed. Care must however be taken in using either

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