Certain plant oils have proved effective in suppressing unwanted oestrus behaviour in mares.
Researchers believe a combination of fatty acids in the coconut and peanut oils used were responsible for the result, which could ultimately provide a practical means of suppressing unruly and difficult behaviour from mares in season.
The oils were used inside the mares’ uterus.
The mare’s oestrus cycle consists of two phases.
In the follicular phase the predominant hormone is oestrogen. It makes the mare receptive to the stallion. It is during this phase that some mares become difficult to manage.
The luteal phase follows ovulation. A “corpus luteum” forms at the site of the recently ovulated ovarian follicle. The corpus luteum secretes progesterone, which prepares the uterus for pregnancy.
If the mare does not become pregnant, the uterus releases hormones – prostaglandins – which break down the corpus luteum (“luteolysis”), allowing the cycle to be repeated.
In the pregnant mare, the uterus recognises the presence of the embryo and does not release prostaglandins. The corpus luteum persists to maintain the pregnancy.
To prevent behavioural signs associated with the mare coming in season it is necessary to maintain adequate levels of progesterone.
This can be achieved by getting the mare pregnant. But pregnancy itself may interfere with the mare’s ability to perform. Other methods include progesterone by injection or the daily administration of synthetic progesterone-like drugs (progestagens) in the food.
Research at the Paul Mellon Laboratory of Equine Reproduction, Newmarket, England, showed that certain plant oils administered into the uterus prevented mares coming back in season.
Sandra Wilsher and Professor Twink Allen were investigating the mechanisms of maternal recognition of pregnancy – in particular, the role of oestrogen on luteal function.
They found that intrauterine administration of oestrogen in fractionated coconut oil prevented mares returning to oestrus.
However, they also found that the coconut oil alone (without oestrogen) had a similar effect, as did peanut oil.
Fractionated coconut oil was most effective when given 10 days after ovulation – luteolysis was delayed in 11/12 mares (92 per cent).
It was not as effective on days 8-12, although the difference was not statistically significant. When administered on the 6th day after ovulation, it inhibited luteolysis in only 25% of mares.
Oestrogen in mineral oil, or mineral oil on its own did not block luteolysis when given 10 days after ovulation.
So it seems unlikely that embryonic oestrogens are important in the maternal recognition of pregnancy.
Fractionated coconut oil and peanut oil each contain various different fatty acids.
The researchers were unable to identify an individual component that was responsible for inhibiting luteolysis. Instead, they suggested that it is likely that a range of fatty acids are capable of causing luteal persistence.
Further work is required to determine how the vegetable oils have this effect. However, it does seem that they may provide a practical way of preventing unruly behaviour in oestrus mares.
Intrauterine administration of plant oils inhibits luteolysis in the mare, S Wilsher, WR Allen. Equine Vet J (2011) 99- 105.
Article originally published on Horsetalk.co.nz in April, 2011.