University of Kentucky College of Agriculture, Food & Environment


Gluck Center > Equine Disease Quarterly > October 2006


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The basic message of “Economics of Broodmare Reproduction” by Dr. Shannon Neibergs in this issue is that increased reproductive efficiency is critical to enhanced profitability of the Thoroughbred breeding operation. Dr. Neibergs’ analysis is derived from the results of a study recently completed by Dr. Karin Bosh while a graduate student at the Maxwell H. Gluck Equine Research Center. Dr. Bosh examined the influence of farm management and veterinary practices on reproductive efficiency. The research was done on 13 Thoroughbred farms in Central Kentucky between 2004 and 2006 and involved 2,000 mares.

The primary goal of the breeding operation is to produce a live foal from each mare for as many years as possible without interruption. The annual live foal rate on the 13 farms was 78%, but only 20% of mares produced a live foal continuously over the first seven years of their reproductive life. On average, mares fail to produce a live foal in two out of seven years. One reason was the drift in a mare’s foaling date, which in the study averaged 13 days. Only 31% of mares experienced no drift, i.e., foaling on the same day or earlier in the subsequent year. These observations suggest a more aggressive approach to breeding maiden, barren, and early foaling mares at the beginning of the season, including judicious breeding on foal heat, would have a beneficial impact on reproductive performance.

Factors which increased reproductive performance over an extended time period were foaling before April of each year and selection of mares with a history of foaling each year. Factors which decreased reproductive performance were the increasing age of the mare and multiple breeding of a mare during the season.

Of increasing impact on performance as it applies to Kentucky is the trend toward increasing book size (the number of mares covered by a stallion during the breeding season). Figures published by the Jockey Club indicate the average book size for Kentucky stallions in 1995 was 35, whereas in 2005 it had risen to 58—compared to a national average of 17. Interestingly, this trend is consistent with an increased live foal percentage, confirming the very high standards of farm and veterinary management, which contributed to an increase in per-cycle pregnancy rate among the population of mares examined.

Breeding costs comprising veterinary and vanning charges represent a very small percentage of the overall annual cost, which includes the stud fee, maintenance of the mare, and annual mare capital cost (depreciation). Yet it is the breeding cost that has the greatest impact on reproductive performance. Investing in the mare over the long term is also emphasized by Dr. Neibergs. However, the considerable unknowns associated with Thoroughbred breeding inevitably confound interpretation of an economic model. They include variation in quality of the broodmare, which influences the purchase and sale value; the length of time the mare is owned; the variation in yearling sale value; and individual investor requirements.

Nevertheless, the study provides a prototype from which farms may develop a program based on high reproductive performance combined with selection criteria for dispersal of poorly performing mares.

Dr. David G. Powell, (859) 257-4757,
Maxwell H. Gluck Equine Research Center
University of Kentucky, Lexington, Kentucky


Second Quarter 2006

The International Collating Center, Newmarket, England and other sources reported the following disease outbreaks:

Contagious Equine Metritis (CEM) was confirmed among mares and stallions on several non-Thoroughbred breeding premises in Switzerland. Abortions attributable to equine herpesvirus- 1 (EHV-1) were reported from France among non-Thoroughbred trotting mares, from Japan on three premises among Thoroughbred mares, and the United Kingdom on five premises. A fatal case of neonatal disease due to EHV-1 and two fatal cases due to EHV-4 were diagnosed in the United Kingdom.

Respiratory disease due to EHV was widely diagnosed among several breeds of horses throughout France and three cases of Coital Exanthema (EHV-3) were diagnosed in the United Kingdom among non-Thoroughbreds.

The outbreaks of Equine Infectious Anemia (EIA) reported from Italy and Ireland in June continue to be investigated and further cases have been diagnosed. The origin in both countries is considered to be the administration of an infected equine biological product. Equine influenza was widely reported in France among several breeds and in a livery stable in the United Kingdom. A sporadic case of Mare Reproductive Loss Syndrome (MRLS) was diagnosed in Kentucky during late April and in New Jersey in June.

West Nile Virus (WNV) infection was diagnosed for the first time in Argentina during February and March. Three deaths resulting from neurological disease were identified among horses on separate premises. In the United States equine cases of WNV were reported by the end of June from Iowa, North Dakota, Wisconsin, and Wyoming with human cases reported in California, Mississippi, and Texas.


EVA Outbreak in New Mexico

An outbreak of Equine Viral Arteritis (EVA) occurred on a Quarter Horse breeding farm in New Mexico in June of this year and the ensuing dissemination of infection to farms both within and outside the state raises significant issues and conclusions. These issues include the management and veterinary procedures employed by the Quarter Horse industry to maximize reproductive performance by extensive use of artificial insemination and embryo transfer, which contributed to the spread of EVA. When an infectious disease outbreak occurs, it is imperative that a prompt and accurate diagnosis is obtained. Preventive measures can then be immediately implemented to restrict the spread of infection and mitigate serious disease and economic losses. Accepting that EVA has now become established within the Quarter Horse population, it will be necessary to introduce a preventive program of vaccination accompanied by appropriate monitoring to determine the extent of this infection within the population.

In early June the farm owner, a veterinarian, became concerned that mares previously identified as pregnant were, upon re-examination, found to be “empty.” By June 16 the increasing number of losses prompted the owner to seek advice as to the possible cause. Sera and semen samples were submitted to the Maxwell H. Gluck Equine Research Center. The center made the recommendation, which was accepted, that shipment of semen from stallions on the farm be halted. On June 23 results revealed very high antibody titers to equine arteritis virus in the majority of the sera, and by June 26 the virus had been isolated from the semen of two stallions. These findings provided very strong circumstantial evidence of recent exposure to the virus, which was later confirmed by examination of paired sera from individual animals.

The owner promptly informed clients that had recently received semen from the infected stallions as well as those who had moved the many donor and recipient mares on and off the farm. The state veterinarian for New Mexico was informed, and the farm was placed under quarantine, prohibiting movement of animals. Following extensive communication and submission of numerous samples to the Gluck Center by farms that had recently received semen or mares from the index farm, it was confirmed that equine arteritis virus infection had become widely disseminated to farms both within the state and in six other states.

With considerable historical information provided by the index farm, it was determined that infection was most likely introduced in late May, with four stallions becoming infected in early June, three of which began to “shed” virus in their semen. Serological examination of over 200 animals on the farm confirmed an extremely high prevalence of infection, with every mare, foal, and stallion on the farm found seropositive. A third of the yearling colts were also positive, with the yearling fillies being serologically negative. Despite the high level of exposure, the reported clinical signs were minimal.  A few animals were reported to have fevers, dependent limb edema, and mild respiratory signs, with the majority of animals experiencing sub-clinical infection. However, the number of pregnant mares losing their pregnancies during early gestation was very high. The initial spread of infection was considered to have been through aerosol transmission from direct contact with animals in the acute stage of infection. This transmission was compounded by the high concentration of animals on the premise. Secondarily, it was thought to be spread by venereal transmission once stallions became semen “shedders” and carriers of equine arteritis virus.

Vaccination of non-exposed yearlings using the modified live vaccine ARVAC® (Fort Dodge Animal Health) was undertaken on the farm, and other animals considered at risk on other farms involved in the disease occurrence also were vaccinated. Because of previous low demand, limited supplies of vaccine were available within the United States, and these supplies were quickly used up, creating an immediate lack of vaccine availability. The supplier, Fort Dodge, has undertaken to manufacture a large batch of vaccine, which should be available in October, in time to initiate a vaccination program prior to the onset of the 2007 breeding season.

Over the last two years there has been increasing evidence of equine arteritis virus infection within the Quarter Horse population when compared to the results of the National Animal Health Monitoring Survey (NAHMS) published in 1998. That survey indicated that the prevalence of infection within the breed was as low as 0.5%.

At a meeting of Quarter Horse breeders, owners, trainers, and veterinarians, held at Ruidoso Downs in New Mexico August 17 coinciding with the annual sales, the feasibility of embarking on a vaccination program of stallions and possibly mares was addressed. Currently this proposal is under consideration. If there is agreement on a policy of vaccination, this policy will need to be implemented prior to the commencement of the 2007 breeding season.

Dr. David G. Powell, (859) 257-4757,, or
Dr. Peter Timoney, (859) 257-4757,

Maxwell H. Gluck Equine Research Center

University of Kentucky, Lexington, Kentucky


Economics of Broodmare Reproduction

A recent study by Dr. Karin Bosh at the Maxwell H. Gluck Equine Research Center examined the influence of management and veterinary factors on Thoroughbred broodmare reproductive efficiency. This article summarizes the development of an economic model as part of the study.

The goal of management is to get the broodmare to conceive at her earliest possible cycle and maintain the pregnancy to produce a live foal. For broodmare economics, a live foal is the critical production measure, because foals are the only source of production revenue. Management practices and veterinary treatments are implemented to achieve early conception. There are many benefits from first cycle conception, including reduced breeding costs from eliminating repeated pre- and post-breeding veterinary treatments and reduced vanning costs. Earlier foaling dates may result in higher valued foals at sale due to greater weanling/yearling maturity and a reduced number of covers a stallion must make within the season. Also, first-cycle conception minimizes the drift in a broodmare’s foaling date over time, which the study has shown to be a significant determinant of live foal rate.

Table 1 presents the typical annual broodmare costs developed for first-cycle conception. Costs were determined by defining best management practices through expert opinion from the panel of farm managers and veterinarians participating in the study. Breeding costs for broodmares conceived on the first cycle are $1,028 for barren broodmares, $902 for maiden broodmares, and $1,249 for foaling broodmares and include veterinary treatments and vanning costs. Costs increase $454 per cycle for each type of broodmare. The maintenance cost includes routine health and farrier costs plus a daily board rate of $26 per day for barren and maiden broodmares. Foaling broodmares have a board rate of $28 per day from March 29 to August 1 to account for the foal by the mare’s side.


Table 1.
Typical First Cycle Conception of Annual Costs by Broodmare Type
Breeding costs
Maintenance cost
Stud fee
Annual Broodmare capital cost (Depreciation)
Total Annual Cost

Two additional major costs of breeding a broodmare are the stud fee and the annualized broodmare recovery cost. The stud fee is the largest production cost and is a highly correlated determinant of yearling value. As stud fee increases, yearling price typically increases. The median stud fee of the broodmares in the study was $30,000 with a live foal guarantee. A broodmare is a capital asset, and depreciation cost recovery rules apply. The depreciation cost recovery period for young broodmares age 12 and under is seven years, and for broodmares over 12, the depreciation recovery period is three years. Depreciation represents the annualized capital cost of the broodmare. The broodmare investment cost is held at $120,000 for all broodmare types, resulting in an annual capital cost of $17,143 for a young broodmare.

Ranking by size of cost shows that the stud fee is the largest annual expense, followed by broodmare capital cost, maintenance cost, and then breeding costs. Although breeding costs are the lowest cost category, they produce the greatest marginal benefit, because these costs maximize reproduction efficiency. Breeders would be willing to invest in higher breeding costs if it increased the likelihood of a live foal.

A broodmare’s annual cost will vary dependent on her quality. Higher quality broodmares have higher value and, therefore, a higher annual capital cost and will also be bred to higher quality stallions with higher stud fees. The annual breeding and maintenance costs are independent of broodmare quality and are the same for all broodmares regardless of quality. Figure 1Figure 1 illustrates the relative importance of breeding and maintenance costs in comparison to broodmare capital cost and stud fee. The graph clearly illustrates that as broodmare quality increases, the stud fees and broodmare capital costs dominate the cost structure of breeding broodmares. For foaling broodmares bred to a stallion with a stud fee of $1,000, the breeding and maintenance costs comprised 88% of the total costs to produce the live foal. For a foaling broodmare bred to a stallion with a stud fee of at least $70,000, the breeding and maintenance costs were less than 10% of the total production costs. The breeding and maintenance costs made up less than 3% of the total production costs for foaling broodmares bred to a stallion with a stud fee of at least $300,000. Similar distributions were observed for maiden and barren broodmares. The level of stud fee/mare quality dictates opportunities for management to influence profitability through cost management practices. At lower stud fee levels, cost management strategies will have greater profitability impacts.   

Assessing reproductive performance in the horse has long been a topic of interest. The Kentucky study examined how farm level management and veterinary practices influence Thoroughbred broodmare reproductive efficiency. The project developed annual breeding and production costs. Work is ongoing to model the multiyear broodmare investment period and to incorporate the broodmare’s reproduction efficiency over time as part of the profitability of a Thoroughbred broodmare investment.

Dr. Shannon Neibergs, (509) 335-6360,
School of Economic Sciences, Washington State University
Pullman, Washington.  


Proliferative Enteropathy in Horses

Lawsonia intracellularis, a well-known pathogen of swine and hamsters, is now frequently recognized within the equine species. It is an obligate, intracellular, curved, gram-negative bacterium that resides freely within the apical cytoplasm of infected intestinal enterocytes, resulting in a proliferative enteropathy. L. intracellularis has been reported to infect several species, including the pig, hamster, rabbit, non-human primate, dog, guinea pig, rat, mouse, fox, white-tailed deer, ferret, and selected birds.

L. intracellularis most commonly causes proliferative enteropathy in foals 3 to 7 months of age, with a higher incidence in those recently weaned. Older horses also can be affected. A wide range of clinical signs can be associated with the disease, including diarrhea, dehydration, lethargy, colic, progressive weight loss, rough hair coat, poor body condition, and pendulous abdomen (potbelly appearance). Clinical abnormalities encountered with proliferative enteropathy include hypoproteinemia, hypoalbunemia, increased serum creatine kinase, anemia, and transient leukocytosis.

Gross lesions caused by L. intracellularis usually involve the distal jejunum, ileum, and proximal colon, although any portion of the intestinal tract can be affected. Pathologic lesions range from multifocal to confluent regions of mucosal hyperplasia. These hyperplastic mucosal regions can form circumferential areas as well as coalescing prominent folds or rugae (corrugated appearance). The affected mucosal surface may demonstrate variable degrees of erosion and/or ulceration. Ulcerated lesions can oftentimes lead to intestinal perforation and peritonitis.

Microscopic lesions observed in horses with proliferative enteropathy include epithelial hyperplasia of crypt glands, with increased numbers of mitotic figures and decreased numbers of goblet cells. Variable numbers of small and curved bacteria are located within the apical cytoplasm of hyperplastic enterocytes and are readily discernible when silver stains (Warthinstarry and Steiner’s) are applied to affected tissues. Minimal to no inflammation involving mononuclear cells is associated with proliferative enteropathy unless concurrent ulceration is present.

Few diagnostic techniques are available to diagnose proliferative enteropathy. Ultrasonographic evaluations of the intestinal tract may reveal segmental to diffuse thickening of intestinal loops, depending on the severity and stage of the disease process. Additional antemortem diagnostic procedures include serology via ELISA and immunoperoxidase monolayer antigen assay, immunohistochemistry and Polymerase Chain Reaction (PCR) testing of fecal smears, mucosal scraping, and/or biopsies. Postmortem diagnostics include close gross evaluation of the entire intestinal tract during necropsy, silver staining of intestinal segments examined histologically, and PCR testing on mucosal scrapings of affected/diseased intestinal segments. PCR testing of mucosal scrapings is considered the most sensitive and specific of all aforementioned diagnostic procedures. L. intracellularis cannot be cultured using conventional media, although it can be cultured on cell cultures under microaerophilic conditions.

The incidence of young equids acquiring an infection with L. intracellularis has increased over the past five years within Central Kentucky. A total of 354 samples were submitted to the University of Kentucky Livestock Disease Diagnostic Center for PCR testing for Lawsonia between December of 2000 and June of 2006. Samples were received from several counties throughout Kentucky. Seventy-four of the 354 submitted samples had positive PCR results (21%). These positive PCR results were obtained from horses residing on 157 farms within six Kentucky counties. Twenty-six out of the 74 positive PCR results were accompanied by necropsy specimens that demonstrated characteristic histologic lesions suggestive of an infection with Lawsonia (Figure 2).

Figure 2

The preferred location for L. intracellularis is within the apical cytoplasm of enterocytes. Using antimicrobials that have the ability to penetrate cellular membranes is strongly recommended. Reports concerning Lawsonia infections in horses consider an Erythromycin-Rifampin combination to be the preferred and most effective treatment regimen. Additional antimicrobials reported efficacious for treatment include chlortetracycline, penicillin, enrofloxacin, chloramphenicol, and ampicillin.

The epidemiology and exact pathophysiologic mechanisms of this disease in horses remains unclear and is the subject of ongoing research efforts.

Dr. Uneeda K. Bryant, (859) 253-0571,

Livestock Disease Diagnostic Center,
University of Kentucky, Lexington, Kentucky.


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Correspondence should be addressed to the editors,
Department of Veterinary Science, Gluck Equine Research Center,
University of Kentucky, Lexington, KY 40546-0099;
Phone (859) 257-4757; FAX (859) 257-8542;


Maxwell H.Gluck Equine Research Center
Department of Veterinary Science, University of Kentucky
Lexington, Kentucky 40546-0099

Main Office (859) 257-4757
Fax (859) 257-8542