Creepy-Crawlies Invade Kentucky Horse Farms: Are Pregnant Mares At Risk Again?

A sure sign of spring: Eastern tent caterpillars are hatching in Kentucky. (South Dakota forestry image)

What on earth could possess them? Researchers tell us today that horses in Kentucky pastures actually do eat eastern tent caterpillars, properly known as Malacosoma americanum (Fabricius). You know them by the damage they do; these little caterpillars spin thick webs on tree limbs...and then munch their way to metamorphosis on emerging young leaves. Once hatched, they fly away, leaving a denuded tree limb behind. But for pregnant mares, they could pose a much greater risk.



Experts at the University of Kentucky today reported that eastern tent caterpillars have begun hatching in central Kentucky and that their population numbers are trending up.

It seems like only yesterday that the horse industry in central Kentucky was devastated by an event known as Mare Reproductive Loss Syndrome (MRLS). The 2001-2002 event caused the loss of an estimated 30 percent of that year's Thoroughbred foal crop, with serious losses suffered by mares of all breeds of horses. After several false tries, the finger of guilt was finally pointed at the caterpillars, which were especially populous that year.

University of Kentucky College of Agriculture entomologist Lee Townsend will be closely monitoring caterpillar development over the next two to three weeks. He and his colleagues anticipate full-grown larvae by the third week of April. From the end of April to the beginning of May, caterpillars will likely leave the trees where they’ve eaten the available foliage and search for additional food to complete their development.

Once the caterpillars have reached these dispersing stages, controlling them becomes much more difficult, Townsend said. If needed, control should target caterpillars while they are gathered together in the trees. Apparently they love ornamental cherry trees, the bright pink-purple blossoms of which are such an exclamation point on spring landscapes.

However, Kentucky's Townsend cautions against spraying too early. That won't work, either. Obviously, timing is everything.

Studies since the 2001-2002 MRLS outbreak revealed that horses inadvertently will eat the caterpillars in the grass. When they do, the caterpillar hairs embed into the protective lining of the alimentary tract. Once that barrier is breached, normal alimentary tract bacteria may gain access to and reproduce in sites with reduced immunity, such as the fetus and placenta. Fetal death or weak foals from these roaming alimentary tract bacteria are hallmarks of MRLS.

UK entomologists recommend that unless horse farm managers have been aggressive in managing eastern tent caterpillars, or removing host trees, they should keep pregnant mares out of pastures bordered by cherry trees or other hosts for the next several weeks.

At many farms, steps have already been taken to cut limbs that overhang or border paddocks. But eastern tent caterpillars are found in many states and horse breeders should be aware of the danger they pose. Apparently the ingestion of the caterpillars does not have known health risks for horses other than pregnant mares.

For a fact sheet about eastern tent caterpillars, as well as periodic updates, please visit the University of Kentucky's special web page on the caterpillar problem. Ohio State University has a helpful web page on how to wage war on eastern tent caterpillars.

What's Killing England's Fell Ponies? Charity Funding for Research Intends to Find Out

Fell ponies look like miniature Freisian horses, but look again: this is a unique breed with a long and glorious history. With long feathers and arched necks, they make the loveliest children's ponies, and the sight of them wandering their native Cumbrian countryside is the stuff that wild horse legends are made of.

But their numbers have dropped since World War II, and the gene pool has shrunken to a bottlenecked puddle. Can this breed be saved? The Horse Trust, a UK charity, has given a donation of more than US$200,000 to the Animal Health Trust, a research center known for its work on strangles and orthopedic problems in horses, and the University of Liverpool. The charity has charged them with the task of finding out how to stop Fells Pony Syndrome (FPS).

FPS is a severe immune system disorder that results in the death of some of the newborn foals, further shrinking the breeding stock available to help the breed survive. The breed is listed as "at risk" by the Rare Breeds Survival Trust.

Foals affected with FPS appear normal at birth but within a few weeks begin to lose condition and suffer diarrhea, coughing and weight loss. Severe anemia and immune dysfunction follows, leading to wasting and finally death. The disease is always fatal.

Studbook analysis and knowledge of affected foals strongly suggests that this is an inherited disease caused by an autosomal recessive genetic mutation. The problem may trace to a single stallion who was a dominant force in the breed. A DNA-based test for this mutation would enable carriers of FPS to be identified and the conception of affected foals prevented.

As well as identifying carriers in the Fell pony population, the project will be used to identify any carriers in other breeds which have been involved in the extensive outbreeding of Fell ponies over the years.

“Breeders are supportive of our attempt to develop a diagnostic test which will help to prevent carrier-carrier matings, one in four of which results in an affected foal,” says project leader Dr June Swinburne, senior post-doctoral equine molecular geneticist at the Animal Health Trust Centre for Preventive Medicine. “Foals affected by the condition inherit an incurable genetic defect which results in severe wasting and a profound anaemia together with multiple infections. Veterinary intervention is in vain and once the condition is diagnosed foals are often euthanized. The gradual but relentless decline in these foals leaves both veterinary surgeons and breeders powerless."

According to the Horse Trust, FPS at the moment is restricted to the Fell pony population but could spread to other breeds at any time. Indeed it may be possible that carriers of the condition already exist in other breeds which have interbred with the Fell pony over many years.

Another rare breed, the Dales pony, and other native British breeds will be randomly tested to detect any further penetration of the defect into the equine population.

To learn more: The Horse Trust has one of the best horse charity web sites anywhere on the web. This remarkably generous and insightful organization funds research and welfare projects that benefit horses all over the world, not just in Britain. The Horse Trust was formerly known as the Home of Rest for Horses and has a long tradition of recognizing the welfare and health needs of horses.

The Fell Pony Society is trying to cope with the devastation of their breeding stock and preserve this lovely breed of pony, which dates all the way to the Roman occupation of Britain.

Photo from the Fell Pony Society.