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.

CEM Investigation Expands to 20 States: Virginia Horse Farms Quarantined

(State of Virginia news alert)

Dr. Richard L. Wilkes, State Veterinarian with the Virginia Department of Agriculture and Consumer Services (VDACS), today placed full or partial quarantines on farms in Floyd and Goochland counties. Mares at these farms have had contact with a stallion in Kentucky that tested positive for Contagious Equine Metritis (CEM).

State animal health officials are trying to verify the location of one other Virginia mare that may have been exposed to the same stallion.

Since the CEM positive stallion was identified in Kentucky last week, animal health officials have identified 20 other states that may have mares that have been exposed to infective semen.

“We don’t know yet if the Virginia mares are infected,” said Wilkes, “but since CEM is not normally found in the US., we have placed the two farms under quarantine to protect other horses while we test the individual mares.”

CEM is a highly contagious venereal disease, which usually results in temporary infertility. Its effects are restricted to the reproductive tract of the mare. Transmission is usually due to sexual contact or artificial insemination but can occur by other types of contact. The disease is diagnosed using special bacterial culturing techniques and has a 100 percent success rate for treatment.

In severe cases, symptoms include an obvious discharge from the vagina. In other cases, mares may be infected with less obvious symptoms or no symptoms at all. Infected mares may fail to become pregnant after breeding or rarely, may abort their foals. Infected stallions usually do not show any symptoms.

The State Veterinarian has quarantined the farms to prevent spread of the disease while exposed mares are evaluated. On farms with isolation capability, only that isolated area is quarantined. Farms that cannot isolate the individual mare are under full quarantine, which restricts movement of any horses on or off the grounds.

For more information on the Virginia suspect cases, click here.

For more information on CEM, click here.

Scroll down to read more posts on this blog containing information from the state of Kentucky, where the infected stallions have been breeding.

Australian Research Confirms Link Between Caterpillars and Equine Fetal Death

An Eastern Tent Caterpillar, typical of the eastern USA; this is the species linked to 2002's Mare Reproductive Loss Syndrome (MRLS) problem on Kentucky horse farms.

Researchers from The University of Queensland have found hairy caterpillars are responsible for causing abortions in Australian mares. Dr. Judy Cawdell-Smith and Professor Wayne Bryden, from UQ's School of Animal Studies, found that mares exposed to caterpillars were likely to miscarry.

"This is an unusual form of abortion that was first reported in Australia in 2004 and is similar to a condition reported in Kentucky in 2002," Dr. Cawdell-Smith said. "Researchers in Kentucky identified Eastern Tent Caterpillars as the cause of the US equine condition, (which came to be known as) Mare Reproductive Loss Syndrome."

Similar equine abortion cases were reported in Australia's Hunter Valley in New South Wales in 2004. The Hunter Valley is Australia's largest Thoroughbred breeding area.

"Studies conducted by veterinary epidemiologist, Professor Nigel Perkins, suggested the abortions were caused by caterpillars or poisonous plants," Professor Bryden said. "No poisonous plants were found on any of the stud farms where mares aborted. Caterpillars were identified as the cause of the US problem but the same caterpillars don't exist in Australia. However, other related caterpillars were found on the affected Australian stud farms.

"If you've ever seen a hairy caterpillar, it is unlikely that a horse would eat a whole one," he continued. "What's more likely is that the caterpillar's exoskeleton – which is much harder to see in the grass – is picked up by the horse while it is grazing. In our studies, both whole caterpillars and exoskeleton caused mares to abort."

The researchers believe ingestion of the caterpillar changes the permeability of the intestinal wall, allowing bacteria to pass into the horse's circulation and through the placenta.

"The subsequent infection caused by the bacteria in the fetus results in abortion," Dr. Cawdell-Smith said. "These bacteria are found in the intestine of mares and normally don't cause a problem. Interestingly, mares that abort have no ill effects or evidence of illness."

Thanks to the University of Queensland for this report.

Mom Always Liked You Best: Wild Horse Research Shows That Mares Pamper Colts More than Fillies

Wild horse mares and foals in Australia are also being studied by the Wild Horse Research Group at the University of Queensland's School of Veterinary Science. GPS transmitters have been attached to some horses to monitor their location and the distances covered. Learn more about the Australian studies at www.wildhorseresearch.com. Australia has more wild horses (and wild camels) than any country on earth. (Photo by Dr Chris Pollitt)

What will a mother sacrifice for her child? Lots more for her son than for her daughter, if she's a wild horse mare.

Researchers from the University of Pretoria in South Africa trekked to the mountains of New Zealand to observe wild horse parental behavior, and suggest that the behavior mirrors human tendencies.

The mares often sacrificed more for colts in order to provide more milk and spent more time playing with colts than with fillies. Physical condition of mares raising colts was often worse than those raising fillies. Researchers presume that the most active and best fed colts developed into the strongest and healthiest stallions. Since horses are polygynous, the mare's genetic influence is increased by a colt who will go on to breed more offspring.

The scientists did mention the catch that if a colt does not grow up to be a dominant male, he will not be able to pass on the mother's genetic code, whereas chances are good that fillies do at least produce a number of offspring over their lifetime.

The scientific research will be published in an upcoming issue of the journal Animal Behavior, but is capsulated in a terrific article prepared by the Discovery channel's web site. Comparisons are made to sex-preference studies in human mothers.

I have read studies like this before but this report is interesting because of the focus not just on the size of colts vs fillies but also the physical activity levels. Do colts play more and grow larger and stronger because they receive better care and nutrition from the mares? Or does their larger size and activity level require more nutrition and attention?

Are You My Mother? Surrogatehood Surges in Sport Horse Scene

Lucinda Fredericks (human on right) hopes to ride her mare Headley Britannia (center) in the Olympics this summer. The other two mares, Bear and Pippa, will be carrying the star event horse's foals, sired by French show jumper Jaguar Mail.

It was a wry chuckle heard round the horse world: On April 1, the venerable British horse sports weekly Horse and Hound stuck its tongue in its veddy Briddish cheek and announced that an exclusive new four-star three-day event would be held in England. What's the hitch? All entrants must prove that record-setting Badminton and Burghley winner Headley Britannia is their mother. April Fool!

Or was it?

In reality, both Headley Britannia and her semen-provider-by-courier, the top French show-jumping stallion Jaguar Mail, could both be competing in Hong Kong at the Olympics this summer, while their offspring are in utero back home in England, thanks to receiver mares. Their first foal was born to the surrogate dam this spring and is already being syndicated by Headley Brittania's owner, Australian team rider Lucinda Fredericks.

One can joke about the popularity of embryo transfer in performance horses, but the reality is that more and more owners of valuable mares--regardless of age--are opting to use their horses as cash cows while the market is strong for sport or performance horses of fashionable bloodlines.

Embryo transfer calls for the breeding of the mare, usually by artificial insemination, when she comes into her normal cycle. The developing embryo is then flushed from her uterus and implanted in a receiver or "surrogate" mare whose cycle coincides with the genetic mother's. The surrogate is often a less valuable horse who might not normally be reproducing. The genetic mother mare is back in training within a few weeks of the breeding and never suffers any of the risks or hardships of pregnancy or motherhood.

Embryo transfer can be done any number of times and there seems to be no limit to the embryos a mare can produce (hence the jokes about Headley Britannia), other than that only one embryo per cycle can be harvested.

The new technology means that mare owners can potentially receive some financial rewards from the mare, just as performance stallion owners harvest semen during a break from showing.

Embryo transfer in the USA took off in Texas and Oklahoma about ten years ago with the reining and cutting horse mares and now owners of show jumpers and dressage mares are lining up for the breeding stocks. Palm Beach Equine Clinic in Wellington, Florida recently acquired a reproduction-specialty facility in Aiken, South Carolina where 90 receiver mares are stabled and undergo the inbound transfer. The embryos travel by Federal Express from Wellington.

Mare owners can breed a young mare a couple of times a year, with potential for more than 15 years of multiple offspring without losing performance time. Mares as young as two may be bred.

There are ethical concerns, of course. In this age of unwanted horses and uncertain finances, do we really need to mushroom the foal crop of warmbloods? Should the ethical decision of "to breed or not to breed" be based on the perceived monetary value of a horse? Is it ok to keep flushing embryos out of an unsound mare if the owner happens to be able to acquire some semen from a fashionable European sire? Are mare owners shrinking the gene pool?

Many mares in training have been on hormones or Regumate-type steroid compounds to control their cycles, and now the trend is to revert to encouraging cycling again, when and if it is convenient, of course.

Many people opted out of breeding this year because they have believed the information fed to them that there is an over-population of horses in this country. Many people are opting for expensive surgery and special shoes and rehab programs for injured horses rather than engaging in the "throw away" economy of horse ownership in which trainers pressure owners to always have a number of horses in training for different divisions or of different ages.

There are no regulations on embryo transfer. If you think your mare is wonderful, and you can afford it, you can keep breeding her and keep flushing her, regardless of whether there is a potential market for her offspring.

The potential benefits of embryo transfer are huge for mares with good breeding value who should not or cannot task the risks of pregnancy or motherhood, particularly mares with laminitis, for whom full-term pregnancy can be painful or life-threatening.

Perhaps mare owners should go through ethical counseling before they make the decision to cash out their mares. Are they simply maximizing a cash investment or are they consciously breeding for the future of the American horse industry?

A demand has been created on the producer side and the veterinary profession is happy to oblige. Whether the demand exists on the buyer end of things remains to be seen. It's a matter of dollars and sense.

To learn more: Read an article in today's Palm Beach Post about the new embryo transfer services offered at Palm Beach Equine Clinic. The article includes a very good explanation of the process and how Palm Beach Equine is managing this new service.

Sport horse mares are better investments than ever, thanks to breeding technology. Palm Beach Post photo.