CEM: Contagious Equine Metritits

This article was originally written for and published in The Quarter Horse Quarterly in 2009

Author Bio:

Jim Dettmer is the owner of Thanks For Com En, double registered Thoroughbred, APHA stallion and AQHA Congress Top Ten, and APHA Championship producer.  Jim runs Dettmers Rising Sun, a breeding facility in Huntington, Indiana, and shows NSBA, APHA and AQHA for a select number of clients.  For more information about standing stallions at Dettmers Rising Sun or breeding information, please visit http://www.dettmersrisingsun.com.

To say the least, this breeding season has been atypical.  Long before the season started, stallion owners and breeding farms were faced with the stark reality of a poor economy, and breedings were clearly going to be down this year. 

Adding insult to injury, there has been an outbreak of contagious equine metritis, (CEM), which has been called by some the most regulated of all equine diseases, even though it poses no risk to humans or to the lives of horses.

Why all the concern?

CEM is a venereal disease that affects mares.  When a mare is infected with CEM, she may have trouble getting in foal or may abort a foal that she is carrying.  It is a metritis, meaning that the infection is limited to the external structures of the horse and does not enter the blood stream. 

Despite much of the attention being on stallions, a stallion does not have any symptoms or effects from CEM.  They are merely carriers for the bacteria.  The implications of a breeding stallion that is a carrier could potentially be huge if he stands to a large book of mares.  It would be a horrible event for a stallion to possibly infect dozens of mares.  However, the risks to mares within the stock horse industry are extremely low if they are using shipped semen.

The cause of CEM is a bacterium called taylorella equigenetalis.  The taylorella bacterium is a relatively sensitive organism.  It is normally susceptible to antibiotics and does not survive well in cool environments.  Those who are familiar with common stallion collection and shipment procedures understand the bacterium will likely be killed by standard breeding practices.  Generally speaking, there are antibiotics in the semen extender used in shipment.  Additionally, the cooled temperature of shipped semen will also kill the bacteria. 

There are some risks associated to breeding shipped semen from an infected stallion though.  Of the over five hundred mares that have been tested that were bred from shipped semen, only three have been found to be positive.  Unfortunately, there has been some question about the validity of some of those tests and independent testing by approved labs was effectively blocked by some state officials. 

Testing and Treatment

As you may have already guessed, treating CEM is a relatively simple process.  It is a matter of using disinfecting scrubs on the affected areas of the mare or stallion as well as topical treatment with an antibiotic ointment.  While some states are requiring oral antibiotics as well, their effectiveness is questionable since the bacterium does not exist in the blood and only in the exterior structures of the horse. 

The difficulty of treating exposed animals comes with regulations imposed by the USDA and state officials.  A practicing veterinarian and approved state veterinarian must oversee testing and treatment because it is such a closely regulated disease.  Owners of affected horses must pay for all of the visits and treatments for their veterinarian and these costs can grow rapidly.  This is despite the fact that many breeding professionals would likely be capable of treating the horses themselves, making the assistance of a practicing veterinarian an unnecessary and costly expense.

Reliability of Testing Among Stallions

The reliability of testing has been a cause for concern by the USDA from the beginning of the outbreak.  This is because much of the case history of CEM in the United States comes from an outbreak among thoroughbred horses in 1979.  Testing of a stallion involves a culture swab of the penis for the bacteria, and then live cover breeding two negative mares who then have to be tested on multiple occasions at a later date.  The USDA requires the live cover breeding because the penis swabs from the 1979 cases were notoriously unreliable. 

However, procedures have improved greatly in the last thirty years, and the USDA is finding that the initial cultures are significantly more reliable than they used to be.  In fact, there has only been one stallion found to be a carrier that was not found on initial cultures. 

There are also many things that can affect the accuracy of the test.  For example, should a stallion happen to be treated by an owner or breeding farm manager before the USDA collects the swab, the antibiotics will make the bacteria significantly harder to catch from the swab because there just aren’t as many active bacteria to find.  Should the treatment on the stallion be ineffective, that stallion could later be found positive after live-covering mares.

Another problem that may have existed was poor culture technique by the practicing veterinarian.  The areas where this bacterium lives are very small and could easily be missed by someone who has not had an opportunity to be exposed to the correct way to collect the cultures. 

Some have also raised questions regarding the chain of custody that cultures are not subject to.  When cultures are collected, they are sealed by the state veterinarian, but inspections by the horse owner or practicing veterinarian and signature are not required.  Because of this break in chain of custody, mistakes would be very difficult to track and eliminate. 

Equity of Costs

When the outbreak was first discovered, Kentucky Commisioner of Agriculture, Richie Farmer requested the Secretary of Agriculture declare this an agricultural animal emergency.  This would allow federal funds be made available to help defray the costs of the outbreak.  Unfortunately, this request has fallen on deaf ears, and there are no plans to reimburse affected states of horse owners for their losses.  Veterinarian costs can easily reach $1000 for mare owners, and are usually higher.  For stallion owners, costs are significantly higher and start at $2000 and go up from there depending on a stallion’s location.  Different states require different types of quarantines which can be more expensive than others.  In fact, some states require exposed horses to go to a specific facility within the state that follows the protocols.  These are the most expensive types of situations. 

The inequity is in that other species such as swine, cattle and sheep, there are similarly regulated diseases that are funded.  This is despite the fact that the horse industry in the United States is a $39 billion a year industry, and has almost ten times the economic impact as the sheep industry. 

The Winds of Change

This outbreak has caused many to look closely at their own breeding practices.  It is believed that CEM could be spread from stallion to stallion by inanimate objects used during the collection of the stallion.  Things like wash buckets used to clean stallions before collection, artificial vaginas, (AVs), and even the dummy mare could be sources of transfer.  It has become increasingly obvious that anything that comes into contact with the stallion’s reproductive organs needs to be clean.  Sanitary procedures such as not sharing AVs between stallions and using bucket liners in wash buckets are necessary precautions that must be made.  Some dummies can be disinfected between stallions if they are made of non-porous materials like vinyl.  However, dummies made of leather will need to have their ends covered by some sort of disposable wrap that is replaced between stallions. 

Mare owners need to be careful to protect themselves as well.  Although the risk of infection is extremely low on shipped semen, the risk of USDA quarantine should be enough to warrant some new questions to stallion owners or breeding managers.  The state of Kentucky has issued a policy that prevents stallions from the state of Wisconsin, the believed source of the outbreak, from coming into the state without negative CEM cultures.  It is advisable that mare owners closely research the stallions they are breeding to.  If there are any connections to Wisconsin or any of the affected farms in Kentucky, the mare owner should be asking for information regarding the risk of exposure the stallion had to CEM.  If the stallion has already been released from USDA quarantine, mare owners can be assured there is no risk of CEM infection.