Page 445 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

420 CHAPTER 2

VetBooks.ir Artificial lighting popular in Thoroughbred stud practice to allow
mares to have light stimulation and encourage early
Day length is an important stimulus for the oes-
trous cycle of the mare and the provision of arti-
expense of stabling (Fig. 2.22).
ficial lighting is the best method of advancing the cycling while being kept at grass and thus avoids the
date of the first ovulation. Several methods have
been described to offer the mare artificial lighting Mare management
conditions. Twenty-four hours of lighting is actually All barren and maiden mares should be examined
detrimental. early in the year per rectum for an active CL and,
A 16-hour light period (16 hours light: 8 hours dark) if necessary, blood samples taken for plasma pro-
starting in early December (northern hemisphere) gesterone levels to confirm the presence of any
(early June in southern hemisphere) advances the first active luteal tissue. Those mares with progesterone
ovulation by around 60–80 days. A 150W clear bulb levels <3.18 nmol/l (1 ng/ml) should be placed on
per 16 m is required. A general rule of thumb is that progesterone withdrawal therapy or GnRH. Those
2
the dark corners of the stable need to have sufficient mares with luteal tissue are cycling and can either
light to be able to comfortably read a book by! be induced into oestrus by exogenous prostaglan-
Adding 2–3 hours of light at the end of the natural din therapy or be monitored for the onset of natural
daylight (as dusk falls) is also effective, but the mares oestrus.
have to be kept outside to receive as much natural
light as possible. Hormonal methods
Another method reported is the ‘flash’ or ‘pulse’ Hormonal treatment regimes added to the end of
system, which delivers 1 hour of light 9.5 hours after the artificial lighting period can further advance the
the onset of darkness. This system is not widely used first ovulation date.
commercially. (Note: If the lighting system fails for
more than 2–3 days, then the mare will go back to Progesterone
where she was before the light treatment.) Daily intramuscular injections of 150–200 mg of
A recently available head-collar light (Equilume™) progesterone in oil +/- 10 mg oestradiol 17β for
utilising a specific wave length blue light has become 10 days, or 0.044 mg/kg of the oral progestagen
altrenogest daily for 10–15 days usually stops pro-
longed spring oestrous behaviour in 1–5 days.
Silastic intravaginal progesterone-releasing devices
2.22
have also been used with success. Following cessa-
tion of the treatment, the onset of oestrous behav-
iour occurs within 1–5 days and ovulation should
occur within 7–10 days. Some clinicians combine
this regime with a prostaglandin injection on the last
day to ensure that any luteinised tissue in the ovary
will be lysed and ovulation will occur. This addi-
tional step is unnecessary if the ovary is monitored
ultra sonographically and no luteal tissue is noted.

Dopamine antagonists
Drugs of this class (e.g. sulpiride and domperidone)
have been used to hasten the onset of the first ovula-
tion in experimental studies. They can be very use-
ful, particularly in the post-foaling mare that is slow
Fig. 2.22 Mare wearing an ‘Equilume™’ to encourage to cycle, and a beneficial side effect of domperidone
early oestrous activity through light simulation. in these mares is the increase in milk production.