Ergot Alkaloids' Effects on Colts and Stallions
By Erica Larson, News Editor • Oct 18, 2011 • Article #28085
Horse breeders in parts of the country frequented by endophyte-infected tall fescue are likely aware of the problems the forage--more specifically the fungus inside the forage--can cause in broodmares. But this toxin's effects on the other half of the breeding puzzle--stallions--remain widely unknown.
Richard Fayrer-Hosken, BVSc, PhD, Dipl. ACT, ECAR, MRCVS, professor of theriogenology at the University of Georgia College of Veterinary Medicine and author of a preliminary study on the topic, spoke Oct. 11 at the Gluck Equine Research Center Veterinary Science Seminar, in Lexington, Ky., where he explained that the effects of ergot alkaloids in colts and stallions do not appear as negative as those in broodmares.
Tall fescue covers an estimated 35 million acres in the United States, including pastures, high-traffic foot paths, golf courses, and backyards. A majority is endophyte-infected (EI). An endophyte is a fungus that lives symbiotically within the host plant and is not visible to the eye. The endophyte produces toxic alkaloids that, when eaten, cause different disorders including tall fescue toxicosis.
In broodmares, Fayrer-Hosken explained, EI tall fescue can cause numerous problems including increased early embryonic mortality, agalactia (poor milk let-down), placental edema (fluid swelling), retained placenta, increased abortion rate, increased gestational length, and increased rate of newborn mortality.
"But what about the stallion?" Fayrer-Hosken asked. "There is little known."
To test what--if any--effect alkaloids have on the stallion, he and a team fed six Quarter Horse stallions either a high-alkaloid feed or a control feed for 70 days. After a 30-day washout period the groups were swapped and received the opposite feed so as to act as their own controls.
Fayrer-Hosken then relayed that using both chilled and frozen semen, the team evaluated the stallions' sperm quality, quantity, motility, and morphology; the stallions' testosterone levels; and their testicular size to see if any negative effects possibly brought on by alkaloid toxicity had developed.
The team was unable to find any negative effects on the stallions as a result of alkaloid consumption, he said. The only statistically significant difference they found was a smaller volume of ejaculate produced by the alkaloid-fed stallions; however, even with the lower volume, sperm quantity remained unchanged between the two groups.
The team then evaluated the alkaloids' effects on eight yearling colts using the same study design. As with the stallions, no health problems were noted in the high-alkaloid fed yearlings. But interestingly, Fayrer-Hosken found that the colts seemed to be more affected by alkaloids than were the stallions.
He explained that 32% of the colts that consumed high-alkaloid feed also had abnormalities in chromosome pairings; some X and Y chromosomes remained unpaired after meiosis rather than pairing up as normally happens.
"What does this mean? We don't know," he noted. "We really want to pursue this further and follow up on it."
In the meantime Fayrer-Hoskin suggested owners be conscious of fescue growth in their pastures, but he doesn't yet recommend completely reseeding fields to eliminate fescue. He relayed that the only horses EI tall fescue has been observed to negatively affect thus far are late-term broodmares, so the forage shouldn't bother other horses. Additionally, he added that tall fescue is an excellent pasture grass and the cost to completely reseed some pastures is prohibitive.
Fayrer-Hosken said he hopes to follow up and obtain additional information about his findings in colts.