Gluck Researchers Study Ways to Advance Breeding Season

Gluck Researchers Study Ways to Advance Breeding Season

Mares are often are maintained indoors under barn lighting until 11 p.m., which fools the mare's reproductive system into activating earlier in the year.

Photo: Anne M. Eberhardt/The Horse

Researchers from the University of Kentucky (UK) Gluck Equine Research Center recently investigated two ways to help advance the breeding season in mares: using recombinant follicle stimulating hormones and by using mobile light therapy.

Using Recombinant Follicle Stimulating Hormone

Gluck Center researchers recently studied the use of recombinant hormones to induce reproductive cyclicity and advance the breeding season in mares. The study, done in collaboration with the University of California and Colorado State University, was to determine the efficacy of an equine recombinant follicle stimulating hormone (reFSH) in noncycling mares housed under natural light conditions.

The transition from reproductive inactivity during the winter to the breeding season can be a lengthy and complicated process. Increased daylight suppresses melatonin (a natural hormone that prevents a mare from cycling in the winter) and allows secretion of reproductive hormones that are necessary to induce ovulation and reproductive cycles. Mares under natural light do not enter the breeding season until late April. The onset of the transition period is characterized by an increase in follicle development and uterine edema.

Veterinarians have developed various management and therapeutic strategies to shift a mare's first ovulation of the year from April to February. The most common management is light treatment, which should begin in December for mares to begin their reproductive cycles in mid-February.

“Even housed under artificial barn light, the mares may still experience normal length of transition period lasting 50 to 70 days or more, prior to the first ovulation of the season,” said Mats Troedsson, DVM, PhD, director of the UK Gluck Equine Research Center and chair of the department of veterinary science. Therefore, there might be a need for alternative treatments of shorter duration.

In their study, the researchers employed 60 deep anestrous (wintertime, noncycling) mares in California, Colorado, and Kentucky from the end of January until one or more pre-ovulatory follicles developed. They divided the mares into two groups and administered each either 0.65 mg of reFSH or a placebo by random selection. The scientists monitored the mares closely by ultrasound until a 35 mm or larger follicle developed, discontinued reFSH treatment, and administered human chorionic gonadotropin (hCG) to induce ovulation. Mares treated with reFSH all developed follicles after a week, and 23 of 30 mares in this group ovulated within 72 hours after receiving hCG. The control group did not develop follicles during the period.

While reFSH proved successful in this study, stimulating early dominant follicles and ovulation in the seasonally anestrous mares, a continued cyclicity failed to appear. “However, the treated mares returned to anestrus following the induced ovulation and followed the calendar of the control group,” Troedsson said. He suggested that continuous treatment might be necessary in mares that fail to become pregnant following breeding on the induced ovulation.

Mobile Light Therapy Efficacy

Using artificial indoor light to speed up mares' transition to breeding season can be time-consuming and costly in electricity, bedding, and labor.

Researchers at the Gluck Center collaborated with Barbara Murphy, BSc, PhD, a researcher at the University College Dublin, Ireland, who recently developed a facemask with blue light directed at a single eye to suppress melatonin production in mares under natural light. The team set out to determine if the facemask was as effective in advancing the breeding season as traditional indoor barn light.

From mid-December to mid-February 2013, the researchers studied 59 Thoroughbred mares, ages 4 to 17, from farms in Lexington, Ky. They divided the mares into three groups. One group was stalled individually under indoor barn light (250 Lux) that remained on until 11p.m.; the second group housed outside wearing the facemask with timed light (50 Lux blue light) from 4:30 p.m. until 11 p.m. daily. The third group was a control group maintained outside in natural light. The researchers performed transrectal ultrasound examinations of the mares' reproductive tract to determine the presence and size of the follicles on the ovaries in conjunction with sampling serum progesterone to confirm ovulation.

In the group exposed to indoor barn light, 14 of 16 mares showed reproductive activity. Twenty of 26 mares wearing the light masks exhibited reproductive activity. The control group only showed four mares in activity. There was no statistical difference between the two light treatment groups, but all treated horses had advanced reproductive cycles compared to the control mares.

“We concluded that the timed low level blue light was as effective as traditional indoor barn light in advancing breeding,” Troedsson said. “In addition, we emphasize that the mobile head gear saves electricity and labor as the horse can remain in pasture.”

Troedsson added that the light facemask is an excellent alternative to indoor barn light as it also allows the horse more outdoor time in its natural environment.

The head piece provides 50 Lux blue light to the right eye and consists of a leather headpiece with a semi-rigid rubber cup with a single blue LED fitted on the inside of the rubber eye cup. The mask is equipped with adjustable velcro down the center of the head piece. It is not yet commercially available.

Shaila Sigsgaard is an editorial assistant for the Bluegrass Equine Digest.

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