Thoroughbred breeding stallions truly have joined the jet set. These four-legged  Romeos are flying from one part of the world to another these days as they perform breeding duties on both sides of the equator. Hundreds of stallions from other breeds also have joined the jet set, but in less dramatic fashion. Because artificial insemination is permitted in most breeds except the Thoroughbred, these stallions remain at home, but their semen is sent to mares in other lands.

Given the speeds that jets can travel, fresh, cooled semen can be collected in Europe and hours later arrive in the United States. Frozen semen also is utilized, but its viability does not yet match that of fresh, cooled semen.

Shuttling Thoroughbred stallions and shipping semen for other breeds have truly "shrunk" the horse world. A Thoroughbred stallion which bred a mare this spring or early summer in the United States might be standing at stud in Australia or New Zealand this fall and winter.

Warmblood stallions in Europe with sterling credentials can be bred to mares in the United States without ever leaving the home farm.

Although shuttling stallions and shipping semen have opened the door of opportunity to breeders in many parts of the world, there is inherent danger involved. Moving stallions from one hemisphere to the other and shipping semen from country to country increase the possibility of spreading infectious venereal diseases, such as contagious equine metritis (CEM) and equine viral arteritis (EVA). (See related articles in The Horse: CEM, March 1998 issue, EVA, February 1999 issue.)

There have been limited problems to date; however, says Peter Timoney, MVB, PhD, FRCVS, of the Gluck Equine Research Center at the University of Kentucky in Lexington, there is "significant risk" of spreading diseases from one country to another both by shuttling stallions and by transporting cooled and frozen semen.

Unfortunately, he says, the temperature at which fresh, cooled semen must be kept for survivability also is the temperature at which disease organisms thrive.

Timoney, an expert in the field of infectious venereal disease, was a speaker on the topic at the Stallion Reproduction Symposium conducted by the American College of Theriogenologists in conjunction with last December’s American Association of Equine Practitioners convention in Baltimore.

Before we hear more from Timoney, it would be well to note how the business of shuttling stallions and shipping semen has grown in the past several years. First, a look at shuttling stallions.

As recently as 1989, only seven stallions were shipped from the Northern Hemisphere to the Southern Hemisphere for breeding. By 1994, the number of shuttled stallions was still under 20. Last year, just four years later, some 80 stallions were shuttled from one hemisphere to the other.

Originally, the shuttles were only to Australia and New Zealand. Today, the geographic locations have grown to include a number of other countries.

Involved in shuttling today, in addition to the United States, Ireland, Australia, and New Zealand, are such countries and areas as Japan, Europe, South Africa, Chile, Argentina, Venezuela, Peru, and Colombia. A stallion, for example, might stand in the United States during our breeding season, then be shipped to Australia for the breeding season "Down Under." Once that season is concluded, he might be returned to the United States, or he could be sent somewhere else, such as Japan, to stand a season.

Shuttling means that a given stallion could conceivably cover 200 or more mares in a single year. When the shipment of semen is involved in breeds that permit artificial insemination, the number of mares that a single stallion could breed in a single year is significantly greater than 200.

A major stimulant in this market involves economics. It takes only basic math to realize that much more money can be made from a stallion covering 150 to 200 mares than from one which covers 50.

The driving force behind stallion shuttling has been Coolmore Stud in Ireland, the Thoroughbred breeding and racing entity founded in the early 1970s by the triumvirate of Robert Sangster, Vincent O’Brien, and John Magnier. In the beginning, much of the emphasis was on developing racehorses, under O’Brien’s tutelage, that could become breeding stallions and mares when their racing careers ended.

The trio was not shy about spending money to get what was wanted in the way of yearlings for Coolmore. They frequently were among the final bidders on high-selling yearlings at Keeneland and Fasig-Tipton sales in Kentucky. They concentrated on Northern Dancer sons and grandsons and soon had reached the point where they, themselves, were selling high-priced yearlings.

Coolmore has continued to grow and enlarge. Today, it operates in Ireland, Australia, and the United States. The U.S. stallion station is Coolmore-owned Ashford Stud near Versailles, Ky. Today, Ashford stands 17 stallions and is planning ultimately to expand to about 25.

At least a dozen of the 17 stallions now at Ashford were to be shuttled abroad when the breeding season in Kentucky ended last month (July), according to Norman Umphenour, DVM, Ashford’s resident veterinarian.

While other farms in America now are playing the game, the major player worldwide remains Coolmore. In 1995, there were 28 stallions shuttled from England or Ireland to Australia—which received the vast majority—and New Zealand. Of that 28, a total of 23 were Coolmore stallions.

That same year, there were 18 stallions from the United States which were shuttled from America to either Australia or New Zealand. Again, Australia was the prime recipient. Of the grand total of 46 stallions shuttled, only seven were sent to New Zealand that year.

From a breeding fee point of view, the shuttling of Thoroughbred stallions appears to be highly successful. Last year, Coolmore’s sire Danehill commanded a $100,000 breeding fee in Australia. Number two on the price list was Ashford Stud’s Woodman—standing part of the year in Australia for a breeding fee of $60,000. The lowest stud fee for a shuttled stallion in Australia last year was Royal Abjar from Rathbarry Stud in Ireland. He stood for a fee of $4,000.

It also appears that the foals of shuttle stallions are commanding higher prices in Australia than foals from domestic horses. During the yearling sale in Sydney over Easter, yearlings from shuttle stallions were responsible for significantly raising the sale average.

Then, too, Timoney believes, there is the matter of improving a good stallion’s chances of siring stakes winners. By putting him first to top mares in the United States or Ireland—or whatever country serves as his home base— then allowing him to spend a season breeding top Australian, New Zealand, or South American mares, the stallion’s odds of producing good runners increase significantly.

Of course, it is not all financial roses. There is a good deal of expense involved in shipping a horse from the United States to Australia or vice versa, for example. The ticket, one way, can run up to $14,000. Then there is the matter of insurance and the cost of quarantine testing procedures that are required before the horse leaves and after it arrives.

One of the first health-related questions that surfaces when discussing shuttling stallions involves an individual horse’s ability to remain fertile when covering up to 200 mares during a year.

To date, according to David Powell, BVSc, also of the Gluck Center in Kentucky, no loss of fertility has been demonstrated in the shuttled stallions. In fact, says Powell, the reverse is true. The shuttled stallions had a higher live-foal rate than did their non-shuttled counterparts.

For the 1992 covering season, Powell said, the shuttled stallions as a group obtained live-foal percentages of 66% from matings in both hemispheres. In 1993, that figure had risen to 70.5%. Those figures exceeded the 61% average live-foal percentage reported by The Jockey Club for North American stallions from the breeding seasons of 1992 and 1993.

Powell said he hasn’t continued a definitive study of live-foal rates involving shuttled stallions, but believes it is now even higher than that reported for 1992 and 1993.

The figures above are a strong indication that traveling around the world to cover larger books of mares does not seem to have a negative effect on a stallion’s sperm production. Another significant factor, Powell believes, involves the excellent care and management involved with the shuttled studs.

Incidentally, the stallion which in the 1993 breeding season had the highest live-foal percentage among stallions that covered 100 or more mares was Woodman. Today, Woodman, as noted above, is a shuttle stallion that stands in the Southern Hemisphere after completing his North American obligations.

Both Powell and Timoney noted that the death loss of stallions being shuttled is low. To date, according to known data, only two stallions have died during the shuttle process in the last decade. Neither was afflicted with a venereal disease. Instead, pneumonia appeared to have played a prominent role.

One of the reasons that many of the stallions do not suffer from the stress of travel, Umphenour believes, is that they are already veterans as a result of their experiences as racehorses. Most of the stallions which arrive at stud farms, he points out, already have been flying from one part of the United States to another and even to foreign countries as part of their racing careers. This means, in many cases, that air travel is old hat to them.

Before being shuttled, the stallions have demonstrated both libido and fertility, so those two issues have been settled.

To date, Umphenour said, Ashford stallions have done very well in handling the stress of traveling and covering a large book of mares in two hemispheres. He said that he does know of cases, however, where either the stress of travel or of the additional covers has been harmful to a stallion’s libido, and he just simply refuses to breed. When that is the case, he says, the solution is a simple one—the horse remains in one hemisphere or the other and is not shuttled.

To date, there has been no known instance where an infectious venereal disease was carried from one country to another by a shuttle stallion.

Will the shuttling of stallions continue to grow? Will there be a saturation point? Timoney and Powell answer in the affirmative to both questions, but with qualifications.

To date, shuttled stallions have been bred to some of the top mares in the countries to which they have been shipped. It is just now that the offspring of many of those matings are making it to the track. If they are successful runners, it is logical to assume that shuttling will increase in the next few years. However, if the number of shuttled stallions increases year after year, a point will be reached where the major market, Australia, will be saturated. There are in the neighborhood of 28,000 to 30,000 Thoroughbred broodmares in the country, and few of them are of a quality to justify breeding fees such as those commanded by Danehill and

However, there is another possibility. As high-quality stallions from countries like the United States and Ireland breed high-quality mares in places like Australia, there might well be an emergence of breeding stock that, in turn, will headquarter in Australia and be shuttled to the United States and Ireland.

It is the potential growth in shuttling stallions and the shipping of semen that sets off some infectious disease alarms with Timoney. Japan is becoming a significant shuttler. CEM, says Timoney, is endemic in Japan.

There is little doubt the South American program will expand. Piroplasmosis, notes Timoney, is present in a number of South American countries.

Semen Transportation

Time to turn now to transported semen and a discussion by Timoney concerning the diseases that can be transmitted through semen as well as by horses involved in live cover.

Timoney opened his talk at the Baltimore gathering with these words: "Of the various modes of transmission involved in the spread of infectious diseases, the venereal route is one of the most effective in ensuring the dissemination of specific pathogens."

The majority of these diseases, he said, are bacterial and include Streptococcus zooepidemicus, Klebsiella pneumoniae, Pseudomonas aeruginosa, Taylorella equigenitalis and Salmonella abortus equi. Listed as viral diseases were equine viral arteritis and equine coital exanthema. One venereal disease—dourine—results from protozoan infection.

However, Timoney added, in addition to the above mentioned diseases, there are a number of others which, though as yet scientifically unproven, could potentially be spread venereally by the stallion:

"Equine infectious anemia (EIA) and piroplasmosis are the most likely diseases in which this might take place," said Timoney. "Both are characterized by occurrence of the carrier state and long-term persistence of the respective etiologic agents in the bloodstream. The latter could provide a ready source of infection for contamination of semen or other body fluids. The remaining diseases which could potentially be spread venereally by the stallion are African horse sickness, Venezuelan equine encephalomyelitis, vesicular stomatitis, and Q fever. In the case of each of these diseases, however, transmission by the venereal route would only be possible during the acute phase of infection when high levels of respective pathogens are likely to be present in the bloodstream.

"Of the group of equine pathogens or diseases which have been confirmed to be venereally transmitted by the stallion, all but contagious equine metritis, dourine, and salmonellosis due to S. abortus equi occur in the USA.

"In the past 20 years, two of this group of diseases have gained a great deal of notoriety because of their impact on the international movement of horses. These are CEM and EVA, both of which are widely considered the diseases of greatest economic significance for breeding horse populations throughout the world at the present time."

Timoney then focused on CEM and EVA in his address.

Contagious equine metritis, he said, is a highly transmissible venereal infection that first was reported in the Thoroughbred breeding populations of England and Ireland in 1977. It is caused by a bacterium that had previously been undescribed—T. equigenitalis. The bacterium is a gram-positive organism with "fastidious growth requirements and relatively unreactive, biochemically." The disease can cause widespread, short-term infertility in mares and can establish the carrier state in both stallions and mares.

Interestingly, the disease is restricted to horses, although donkeys have been infected with CEM under experimental conditions. However, attempts by researchers to infect cattle, sheep, swine, and cats in the same manner have been unsuccessful.

Since CEM was first reported in 1977, it has been recorded in the horse populations of various countries throughout the world. Some of the countries—Australia and the United States to be specific—have eradicated CEM from their respective horse populations.

Timoney gave this description of efforts to eradicate CEM, once it had been discovered and identified:

"Shortly after CEM was first recorded in the late 1970s, voluntary Codes of Practice were developed by certain countries—initially France, Ireland, and the United Kingdom—which provided guidelines for the prevention and control of CEM in breeding horse populations. The principal aims of these codes were twofold: firstly, to screen all stallions and broodmares for the presence of T. equigenitalis and identify any clinically affected mares or asymptomatic carrier stallions or mares; and secondly, to isolate and treat and culture positive animals. Better standards of hygiene on breeding farms were advocated and the use of disposable materials such as specula gloves was recommended to minimize the risk of indirect transfer of infection. Where permissible, the use of artificial insemination was identified as a means of reducing the chances of transmission of T. equigenitalis.

"In most countries which have implemented a rigorous prevention and control program for CEM, the incidence of the disease has been significantly reduced and in certain cases, eradicated."

While diligence and good management practices have brought CEM under control, if not eradicated, in many countries, there has been one failure for science. An effective vaccine to protect against CEM has not been developed.

The shuttling of stallions from country to country, Timoney believes, increases the danger threshold for an outbreak of CEM somewhere in the world.

Timoney offered this suggestion: "Countries which have never had CEM or have successfully eradicated it should ensure that all stallions and mares imported from countries in which CEM is known or suspected to occur, are adequately screened for T. equigenitalis before release from post-importation quarantine.

"While this should apply to all horse breeds, special attention must be paid to non-Thoroughbreds in which there is greater likelihood of infection. Testing of stallions must include both bacteriological examination and test breeding to two susceptible mares, which should be monitored clinically, bacteriologically, and serologically for T. equigenitalis infection.

"Experience gained over a significant number of years has shown that the greatest risk of reintroducing CEM to the United States is through the importation of a carrier stallion and to a much lesser extent, a carrier mare. Regardless of pre-export breeding or testing history, all imported stallions and mares must continue to be rigorously screened for T. equigenitalis in post-importation quarantine, if this country is to maintain its freedom from CEM."

We turn now to another feared venereal disease—equine viral arteritis or EVA, which causes mares to abort. EVA first was confirmed as a separate viral infection of horses in 1953 following an extensive outbreak of respiratory disease and abortion in Standardbred breeding stock in Ohio. In addition to causing mares to abort, the disease can establish a long-term carrier state in stallions.

The good news involving EVA, as opposed to CEM, is that a modified live virus vaccine was developed to prevent its occurrence.

Timoney added that: "The risk of introducing equine arteritis virus onto a premises and exposing stallions and broodmares to the virus can be greatly reduced by isolating any horses returning to the farm from other breeding premises, sales, shows, or racetracks for four weeks. The importance of the carrier stallion in the epidemiology of equine arteritis virus (EAV) and the propensity of the virus to establish the carrier state in a high percentage of infected stallions underscore the importance of preventing and controlling the transmission of EVA in the breeding shed. Major features of current EVA control programs are the identification of carrier animals in a breeding stallion population and annual vaccination of all at-risk breeding stallions at least 28 days before the start of each breeding season. Teaser stallions should also be vaccinated against EVA on an annual basis. Furthermore, first season stallions should be checked for the carrier state before being used for breeding."

Timoney then turned his attention to cooled and frozen semen with these somber, warning comments:

"In view of the significant risk of introducing equine arteritis virus into a susceptible horse population through the use of cooled or frozen semen, appropriate measures need to be taken to prevent outbreaks of EVA resulting from insemination of mares that have not been previously immunized against the disease. There is growing evidence that a percentage of imported frozen semen—especially from Warmblood stallions—is contaminated with equine arteritis virus. In many instances, horse owners and breeders are breeding their mares with imported semen in complete ignorance of its infectivity status for equine arteritis virus and the potential risks involved."

Timoney noted that only two states—Kentucky and New York—have established specific control programs for EVA. Such programs, he feels, should be nationwide.

So, once again, we arrive at a downside to shuttling of breeding stallions and transportation of semen throughout the world. As the number of shuttled stallions increases and as the volume of transported semen continues to rise, so will the risk factors for spreading contagious disease.

About the Author

Les Sellnow

Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at or by calling 800/582-5604.

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