Veterinary session

The sexual activity of mares interrupts from late autumn until the next spring. The spontaneous resumption of the cyclic ovarian function naturally starts in the middle of April, which means several problems for stud farms, because the mares cannot be bred at the beginning of the official breeding season. It is the goal to achieve an official birthday for foals at 1st January (Northern Hemisphere) each year, in order to produce mature yearlings and precocious two- year- old horses. Foals from a late conception in the year are obviously handicapped against their older counterparts.

In order to shorten the transition period, breeders and veterinarians perform the following methods: gestagen treatment, luteolysis of the persistent corpus luteum, slow release GnRH implant and light program.

Additional light, starting in the middle of December, can hasten the first ovulation of the year by 2 ½ months. Recent studies indicate, that light of 446 – 477 nm wavelength (blue light) is the most effective light to prevent melatonin production, which is responsible for anestrus during winter. Based on this finding a special mask has been developed, emitting a blue coloured light to one eye of the mare between 16 and 23 p.m. every day for minimum 90 consecutive days.

We allotted 15 mares into the following three experimental groups:

1. Equilume group: five mares have been treated with the Equilume light masks (from 3rd December until 26th March).

2. Regumate group: five mares received 22 mg altrenogest daily for 15 consecutive days, followed by a single luteolytic dose of PGF2alpha.

3. Untreated control group: five mares received no treatment at all.

All mares have been checked daily for heat symptoms and signs of cyclic activity. Blood samples have been taken once a week for Progesterone analysis.

All five light treated mares started cycling, three of them in the middle of March, and the other two in April. All of them have been inseminated, four became diagnosed as pregnant, the fifth mare returned to heat several times and is still waiting for pregnancy diagnosis. Out of the five Regumate treated mares, four started to cycle already in early March, one did not show cyclic ovarian activity until the end of April. By end of June, all the five mares were cycling and have been inseminated. All of them are diagnosed as pregnant.

In the untreated control group, two animals were cyclic already in February, the third started to cycle in the middle of April and the other two did not cycle until end the of June.

Our preliminary experiment demonstrates, that both, the Equilume light treatment and the long-term Regumate-treatment, are able to trigger the cyclic ovarian function early in the transition period. Further experiments are needed to elucidate the background mechanism of these treatments and to refine the experimental setup on a larger group of animals.