Contagious equine metritis in Australia.

Contagious equine metritis (CEM) was first diagnosed in Australia in August 1977 and it has since been found on 6 farms in 3 states, having been isolated from about 24 mares and 2 stallions. Details are given of the epidemiology and control procedures used to combat CEM on one farm. Difficulty was experience in successfully treating one infected stallion; this was thought to be associated with inadequate cleaning and treating of the diverticulum of the urethral fossa. Introduction of the disease has had far-reaching consequences and may well result in the adoption of routine bacteriological tests on stallions and mares of unknown or dubious breeding history and other measures to minimize the possibility of spread between farms.     

Retrospective and statistical analysis of breeding management on the Italian Heavy Draught Horse breed

This study investigated some aspects of breeding management in the Italian Heavy Draught Horse breed, aiming at improving its efficiency at stud farm level. A first aim was to evaluate the risk of unsuccessful reproduction in mares after an early (3 years) or normal (4 years) age at first foaling, in interaction with different stud rearing systems. A second objective was the examination of the mean time length in which young 2-year-old stallions maintain a genetic superiority on older proven stallions, identifying a ‘genetic lifespan’ in which young stallions can be safely used for reducing the cost of services. Reproductive performance at first and second foaling of 1513 mares were used. Mares had a normal first foal at 3 (n = 745) or 4 years of age (n = 768) in stud farms on the basis of stable (n = 488), feral (n = 345) or semi-feral (n = 680) rearing systems. Logistic regression analysis was performed by modeling the risk of unsuccessful reproduction in the subsequent season (i.e., results at second foaling), as affected by the interaction of age at first foaling × rearing system (six classes). Genetic lifespan of young stallions was estimated by regressing the least square means from a mixed model analysis for repeated measures of individual differences in ‘total merit’ estimated breeding values (EBVs) between young stallions (mean no. of 45/year) and the mean EBV of all proven stallions in a given year of genetic evaluation (mean no. of 483/year). Young stallions born between 1999 and 2005 were used, following each generation (i.e., birth year) from 2 to 7 subsequent yearly genetic evaluations. In comparison with the best reproductive success of second foaling at 4 years in stable systems, the greatest risk of unsuccessful reproduction was at 3 years in feral (+167%) and 3 years in semi-feral conditions (+91%). Young stallions showed a 0.50 s.d. greater EBV at the first evaluation than proven stallions, with a mean annual decrease in EBV of 0.07 s.d./year on proven stallions. Optimal breeding management could be obtained in stud farms by limiting foaling at 3 years, particularly in feral and semi-feral rearing systems, and using young stallions for 3 to 4 years to maintain a perceptible selection differential with older proven stallions and to reduce cost of services. Later, the selection differential with proven stallions become less consistent and genetic improvement could be slowed down.     

A survey of the fertility of Icelandic stallions

Very limited information is available on the breeding performance of Icelandic stallions, let alone the effect that management practices may have had on such performance. As an extensively kept, largely genetically isolated breed of horse it provides a good model for the study of factors that affect reproductive performance without the additional complication of selective breeding, infectious infertility and breed effect. A survey was conducted using 27 Icelandic stallions covering 1590 mares within the normal Icelandic breeding system (May to September). During the season, stallions cover mares within three periods of time, each period being of a similar length (average 35.5 days). During period 1, mares are covered in hand and at pasture. During periods 2 and 3, all mares are covered at pasture. The overall fertility rate for Icelandic stallions was calculated. The effect of a range of variables on fertility was investigated statistically using a number of models in an attempt to minimise the effect of confounding factors. An overall adjusted fertility rate for Icelandic stallions of 67.7% was obtained. The following factors were shown to have a significant effect on fertility: age of mare (P<0.001), training level of stallion (P<0.05) and method of breeding (P<0.05). For some individual stallions reproductive status of the mare also had a significant (P<0.001) effect. Many of these factors have been observed to effect FR in other more intensively managed equine populations. However, the less dramatic detrimental effect of age and the lack of a significant effect of mare reproductive status in most stallions suggests that infertility problems are less evident in Icelandic mares, possibly due to less emphasis on selection for athletic performance and the accepted culling of subfertile stock.     

Administration of oxytocin immediately after insemination does not improve pregnancy rates in mares bred by fertile or subfertile stallions

It is probable that reduced pregnancy rates in mares bred to subfertile stallions is attributable, in part, to the reduced number of normal spermatozoa that colonize the oviduct. Administration of oxytocin stimulates both uterine and oviductal contractility. The hypothesis that oxytocin may enhance sperm transport to/into the oviducts, and thereby increase pregnancy rates, was tested in 2 trials. For both trials, fertile estrous mares with follicles > or = 35 mm in diameter were inseminated once at 24 h after administration of 1500 to 2000 U hCG. The inseminate dose was limited to 100 million spermatozoa in order to lower pregnancy rates and thus increase the chance of detecting a treatment effect. Pregnancy status was determined by transrectal ultrasound examination 14 to 16 d after insemination. In Trial 1, 49 mares were inseminated with 4 mL extended semen from 1 of 3 stallions (1 fertile and 2 subfertile males). Immediately after insemination, the mares were administered either 20 U oxytocin or 1 mL saline intravenously. In Trial 2, 51 mares were inseminated with 4 mL extended semen from 1 of 4 stallions (1 fertile and 1 subfertile male used in Trial 1, and 2 additional fertile males). Immediately after insemination, and again 30 min later, mares were administered either 5 U oxytocin or 0.25 mL saline intramuscularly. To test for effects of treatment with oxytocin and for the interaction between semen quality and treatment, a generalized linear mixed regression model was used that accounted for the split-plot design (treatment within stallions), the random effect of stallion, the fixed effect of semen quality, the binary outcome of a single breeding trial, and the varying number of trials per stallion/treatment groups. Three treatment protocols or regimens were used: placebo, 5 U oxytocin injected twice intramuscularly, and 20 units oxytocin injected twice intravenously. Semen was classified as high (fertile stallions) or low (subfertile stallions) quality. No interaction between semen quality and treatment was detected (P > 0.10). The pregnancy rate of mares treated with oxytocin immediately after insemination was 30% (15/50) compared with 50% (25/50) for mares treated with saline immediately after breeding. Administration of oxytocin did not affect pregnancy rates (P > 0.10).     

Sexual behavior following introduction of a stallion into a group of mares

A rested stallion was introduced daily for 30 days into each of three herds of 20 mares. Observations of sexual and mating behavior were made for one hour. The stallion remained with a herd until another stallion was introduced the following day. Other mares were isolated from stallions and were bred by artificial insemination. The diameter or growth rate of the preovulatory follicle for the six days preceding ovulation and the length of the interovulatory interval for mares which did not become pregnant were not affected significantly by the presence of a stallion. The number of breedings per hour of observation (2.4 ±0.2) and the length of the interval from introduction of a stallion into the herd of mares to first breeding (12 ±1 min) were significantly different among stallions, but the length of the interval between breedings (17 ±2 min) was not. The mean number of breedings per stallion per hour was not affected significantly by the number of posturing (estrous) mares. The number of times that the stallion rebred the same mare when more than one mare postured during the observation hour (49%) was greater (P<0.01) than what would be expected to occur by chance (30%). The hypothesis that breeding occurs preferentially in those estrous mares that are closest to ovulation was not supported, except for significantly lower breeding activity in posturing mares on days 8 and 7 before ovulation and on days 0 (day of ovulation) and ?1 (26% bred) than on days 6 to 1 (52%).     

The dynamics of hoof growth of the primitive Konik horses (Equus caballus gmelini Ant.) in an annual cycle

The annual growth rate of the horny wall of the hoof was investigated in 38 horses—31 mares and seven stallions. Experimental subjects were Konik horses kept in a conservative breeding herd. The horses hooves of both limbs: the right fore limb and the right hind limb were measured and next growth rate of the horny wall was analysed at five points of the hoof capsule. On the basis of Principal Component Analysis it was found that the subjects needed to be considered in three groups: three-year old mares, older mares and stallions. Next the growth increments were averaged in each investigated group and compared. The dynamics of hoof horn growth turned out to be the highest in the group of young mares, followed by the group of stallions and the group of adult mares. In the winter months the lowest growth increment of the hoof horn was observed in all the analysed groups. In the period of the elongating solar day, i.e. from May to July, the growth was rapid and reached the highest values. Starting from August the growth of the hoof horn decreased.     

Contagious equine metritis--outbreak of the disease in Kentucky and laboratory methods for diagnosing the disease.

Contagious Equine Metritis (CEM) was initially reported during the 1977 breeding season in England (Crowhurst, 1977) and Ireland (Timoney, Ward & Kelly, 1977. The disease has also been diagnosed in France and Australia (Huges, Bryden & MacDonald, 1978). The first occurrence of CEM in the United States followed the importation or 2 stallions from France late in 1977 which resulted in an outbreak early in the 1978 breeding season (Swerczek, 1978). Mares usually develop clinical signs of CEM 8--10 days after being covered by an infected stallion, when a copious, greyish discharge is seen. Other mares may not show any outward signs of disease, but may have a shortened dioestrous period. Many mares recover spontaneously from the disease, but a small proportion become carriers of the CEM organism. The stallion does not show any clinical signs of disease, but remains a carrier. In this paper we recommend various laboratory procedures for the diagnosis of CEM in mares and stallions.     

Tests for cooperative behaviour between stallions

Breeding groups with multiple stallions occur sympatrically with single-stallion breeding groups in feral horse, Equus caballus, populations. Mutualism and reciprocal altruism between stallions have been proposed to explain the origin and functioning of multistallion bands. However, empirical support for these hypotheses is contradictory and incomplete. Furthermore, there are no explicit tests of the predictions that each hypothesis makes about stallion behaviour and social structure. We compared nine multistallion and 18 single-stallion bands in the Kaimanawa Ranges, New Zealand. Compared with agonistic behaviours, affiliative behaviours were relatively unimportant in the relationships between stallions within bands. The number of stallions in the band did not have a positive influence on mare group size, stability, home range quality or reproductive success in bands. Furthermore, there was a positive relationship between aggression ('intolerance') by the dominant towards subordinate stallions and the subordinates' effort in mare group defence ('helping') but a negative relationship between helping effort by subordinates and their proximity to, and mating with, the bands' mares. Therefore, the predictions of the mutualism and reciprocal altruism hypotheses were not supported. Indeed, for some of the predictions we found the opposite outcomes to be true. Multistallion bands had significantly poorer reproductive success, and dominant stallions were less tolerant of subordinates that helped most and reduced their access to mares. Nevertheless, in all other respects Kaimanawa stallions in multistallion bands behaved like those described elsewhere. Thus, we reject cooperative hypotheses for multimale breeding groups in horses and discuss the mate parasitism and consort hypotheses as better alternatives. Copyright 2000 The Association for the Study of Animal Behaviour.     

Equine frozen semen: freezability and fertility field results

The freezability of stallion semen defined as the number of selected ejaculates/total number of ejaculates frozen from 161 different stallions was analyzed. Of the stallions, 19, 30, 27 and 24% had a freezability of 0%, 0 to 33%, 33 to 66%, over 66%, respectively In 85 different stallions, the correlation of freezability between first and second year was 0.60 (P < 0.001). The relationship between fertility with fresh and frozen semen and freezability was analyzed in 40 stallions whose freezability and fertility information was recorded during 5 years. There was a strong relationship between fertility of fresh semen and semen freezability (P < 0.001). However, the relationship between fertility of frozen semen and freezability was not as marked (P < 0.05). Analysis of the field fertility per cycle results when mares were bred with 300 or 150 x 10(6) total spermatozoa at different frequencies until ovulation indicated that mares that were inseminated 2 times or more per estrus show an improved fertility in comparison with mares inseminated only once (34%, n = 1576 vs 26%, n = 626; P < 0.001). Foaling rate when mares were inseminated with frozen semen (1858 mares during 8 breeding seasons) was mainly influenced by mare age (< 16 years: 54% vs >/= 16 years 42% p < 0.001). Date of first insemination (before May 15: 58% vs after May 15: 37%) also had a significant effect on foaling rate (P < 0.001).     

The equine frozen semen industry.

Recent acceptance of frozen semen as a method to produce registered foals by two of the worlds largest breed associations, the American Quarter Horse and American Paint Horse, has stimulated new interest in frozen semen technology. This review will: (a) attempt to identify the major impediments to the development of the frozen semen industry, (b) suggest alternative methods for marketing and application of frozen semen, and (c) present the results of a recent study in our laboratory. The objective of which was to compare pregnancy rates of insemination with cooled and frozen semen. Major impediments to the development of the frozen semen industry include 1. Lower fertility with frozen semen as compared to cooled semen for many stallions. 2. Increased costs associated with management of mares for AI with frozen semen using current insemination protocols. 3. Unfavorable marketing practices for frozen semen. Reports of fertility with cooled transported semen in commercial breeding programs indicate seasonal pregnancy rates ranging from 60 to 90%. We compiled data from three commercial transported cooled semen programs in which semen from 16 stallions was used for insemination of 850 mares throughout North America by local veterinarians. During the 1999 and 2000 breeding seasons, first cycle and seasonal pregnancy rates of 59.4 and 74.7% were obtained. During that same period, first cycle and seasonal pregnancy rates of 51.3 and 75.6% were obtained following insemination of 876 mares with frozen semen from 106 different stallions processed by our laboratory and distributed through our commercial distribution program. First cycle and seasonal pregnancy rates were higher for mares bred outside of North America than for mares bred within North America (53.5 and 81.9 versus 49.4 and 65.6%, respectively). Seasonal pregnancy rates were higher presumably because of the better mare management employed for mares bred with exported semen and the fact that some of the domestic mares were switched to cooled semen insemination after a failed first cycle attempt with frozen semen. These data support the position that comparable seasonal pregnancy rates may be obtained using frozen and liquid cooled semen in a commercial setting.     

Management and fertility of mares bred with frozen semen.

Semen quality, mare status and mare management during estrus will have the greatest impact on pregnancy rates when breeding mares with frozen semen. If semen quality is not optimal, mare selection and reproductive management are crucial in determining the outcome. In addition to mare selection, client communication is a key factor in a frozen semen program. Old maiden mares and problem mares should be monitored for normal cyclicity and all, except young maidens, should have at least a uterine culture and cytology performed. Mares with positive bacterial cultures and cytologies should be treated at least three consecutive days when in estrus with the proper antibiotic. With frozen semen, timing the ovulation is highly desirable in order to reduce the interval between breeding and ovulation. The use of ovulation inducing agents such as human chorionic gonadotropin (hCG) or the GnRH analogue, deslorelin, are critical components to accurately time the insemination with frozen semen. Most hCG treated mares ovulate 48h post-treatment (12-72h) while most deslorelin (Ovuplant) treated mares ovulate 36-42h post-treatment. However, mares bred more than once during the breeding cycle appear to have a slight but consistent increase in pregnancy rate compared to mares bred only once pre- or post-ovulation. In addition, the "capacitation-like" changes inflicted on the sperm during the process of freezing and thawing appear to be responsible for the shorter longevity of cryopreserved sperm. Therefore, breeding closer to ovulation should increase the fertility for most stallions with frozen semen. Recent evidence would suggest that breeding close to the uterotubal junction increases the sperm numbers in the oviduct increasing the chances of pregnancy. Post-breeding examinations aid in determining ovulation and uterine fluid accumulations so that post-breeding therapies can be instituted if needed. Average pregnancy rates per cycle of mares bred with frozen semen are between 30 and 40% with a wide range between sires. Stallion and mare status are major factors in determining the success of frozen semen inseminations. Pregnancy rates are lower for barren and old maiden mares as well as those mares treated for uterine infections during the same cycle of the insemination. To maximize fertility with frozen semen, a careful selection of the stallions and mares, with proper client communication is critical. Dedication and commitment of mare owner and inseminator will have the most significant impact on the pregnancy rates.     

Reproductive performance of Friesian mares after retained placenta and manual removal of the placenta

Because the incidence of retained placenta in Friesian mares is estimated to be high, and no reports have been published on the reproductive performance of Friesian mares after retained placenta, we studied postpartum reproductive performance in Friesian brood mares with (n = 54) and without (n = 50) retained placenta. We defined a retained placenta as the failure to expel all fetal membranes within 3 h after the delivery of a foal. We subdivided the group of mares with retained placenta into mares in which the placenta had been removed manually (n = 30) and mares in which it had not (n = 24). Within each group, we compared reproductive performance after breeding in the foal heat and breeding in a subsequent heat. We also recorded the age of the mares, number of mares treated with antibiotics after insemination, and number of mares treated with prostaglandins. The interval between delivery and conception, efficacy rate (number of served cycles divided by the number of mares that had a positive pregnancy diagnosis), seasonal pregnancy rate, pregnancy rate after first insemination, pregnancy loss rate, and foaling rate did not differ between mares with and without retained placenta or between mares with and without manual removal of the retained placenta. Within each group, the pregnancy rate after first insemination did not differ between breeding for the first time in the foal heat and breeding for the first time in a subsequent heat. We concluded that reproductive performance did not differ between (1) Friesian mares with and without retained placenta and (2) Friesian mares with and without manual removal of the placenta. With regard to reproductive performance, retained placenta and manual removal of the placenta are not valid reasons to avoid foal heat breeding in Friesian mares.     

Capacitation, acrosome function and chromatin structure in stallion sperm

In general, fertility in breeding stallions is lower and more variable than in the other farm animal species, primarily because selection is based on pedigree, looks and/or athletic performance, with little consideration of fertility or fertility potential. Moreover, because the average stallion breeds only a limited number of mares per year and in-field fertility is influenced significantly by non-stallion factors such as management and mare fertility, meaningful fertility data are hard to come-by. Unfortunately, generating usable figures would involve impractically high costs, time and numbers of mares. Instead, a breeding soundness examination (BSE), based on assessments of sperm number, motility and morphological normality and of mating ability, is often carried out with the ostensible aim of identifying animals with the "potential for good fertility". In fact, the BSE generally succeeds only in ruling out those stallions with a very clear reason for sub-fertility, and still fails to identify some seriously sub-fertile animals. Thus, the routine BSE has very limited use as a predictor of subsequent fertility. This paper reviews assays developed for identifying capacitated, acrosome-reacted and DNA-damaged sperm, and assesses their utility for improving our ability to predict a stallion's fertility prior to the onset of his breeding career.     

Association between population structure and allele frequencies of the glycogen synthase 1 mutation in the Austrian Noriker draft horse

The aim of this study was to determine the allele frequency of the glycogen synthase 1 (GYS1) mutation associated with polysaccharide storage myopathy type 1 in the Austrian Noriker horse. Furthermore, we examined the influence of population substructures on the allele distribution. The study was based upon a comprehensive population sample (208 breeding stallions and 309 mares) and a complete cohort of unselected offspring from the year 2014 (1553 foals). The mean proportion of GYS1 carrier animals in the foal cohort was 33%, ranging from 15% to 50% according to population substructures based on coat colours. In 517 mature breeding horses the mutation carrier frequency reached 34%, ranging on a wider scale from 4% to 62% within genetic substructures. We could show that the occurrence of the mutated GYS1 allele is influenced by coat colour; genetic bottlenecks; and assortative, rotating and random mating strategies. Highest GYS1 carrier frequencies were observed in the chestnut sample comprising 50% in foals, 54% in mares and 62% in breeding stallions. The mean inbreeding of homozygous carrier animals reached 4.10%, whereas non‐carrier horses were characterized by an inbreeding coefficient of 3.48%. Lowest GYS1 carrier frequencies were observed in the leopard spotted Noriker subpopulation. Here the mean carrier frequency reached 15% in foals, 17% in mares and 4% in stallions and inbreeding decreased from 3.28% in homozygous non‐carrier horses to 2.70% in heterozygous horses and 0.94% in homozygous carriers. This study illustrates that lineage breeding and specified mating strategies result in genetic substructures, which affect the frequencies of the GYS1 gene mutation.     

The epidemiology of contagious equine metritis (CEM) in England 1977--1978).

Following an outbreak of CEM in England during 1977 a Code of Practice was introduced to control the disease in 1978. The Code recommended a bacteriological screening programme for Thoroughbred mares and stallions and improved standards of hygiene on the stud farm. As a result of the implementation of the Code a number of asymptomatic carrier mares was detected. Stallions which had transmitted CEM in 2977 and were treated did not transmit the disease during 1978. Two small outbreaks of CEM were reported during the 1978 breeding season.     

Quality and fertility of cooled-shipped stallion semen at the time of insemination

Stallion semen processing is far from standardized and differs substantially between AI centers. Suboptimal pregnancy rates in equine AI may primarily result from breeding with low quality semen not adequately processed for shipment. It was the aim of the study to evaluate quality and fertility of cooled-shipped equine semen provided for breeding of client mares by commercial semen collection centers in Europe. Cooled shipped semen (n = 201 doses) from 67 stallions and 36 different EU-approved semen collection centers was evaluated. At arrival, semen temperature was 9.8 ± 0.2 °C, mean sperm concentration of AI doses was 68 ± 3 x 10⁶/ml), mean total sperm count was 1.0 ± 0.1 x 10⁹, total motility averaged 83 ± 1% and morphological defects 45 ± 2%. A total of 86 mares were inseminated, overall per season-pregnancy rate in these mares was 67%. Sperm concentration significantly influenced semen motility and morphology at arrival of the shipped semen. Significant effects of month of the year on volume, sperm concentration and total sperm count of the insemination dose were found. The collection center significantly influenced all semen parameters evaluated. Semen doses used to inseminate mares that became pregnant had significantly higher total and progressive motility of spermatozoa and a significantly lower percentage of morphological semen defects than insemination doses used for mares failing to get pregnant. Results demonstrate that insemination with semen of better quality provides a higher chance to achieve pregnancy. Besides the use of stallions with good semen quality, appropriate semen processing is an important factor for satisfying results in artificial insemination with cooled-shipped horse semen.     

The reproductive performance of Thoroughbred mares treated with intravaginal progesterone at the start of the breeding season

The objective of this study was to investigate the effects of intravaginal progesterone on the reproductive performance of transitional Thoroughbred mares on commercial stud farms. Two hundred twenty-seven (227) non-lactating transitional Thoroughbred mares aged between 4 and 18 y (mean 9.4 ± 3.2 y) located on three stud farms in the Waikato region of New Zealand were used in the study performed during four consecutive breeding seasons (2007-10). Mares were age-matched in pairs and either treated with an intravaginal progesterone releasing device (Cue-Mare, 1.72 g progesterone, 10% w/w) for up to 10 d (Treated; n = 126) or left untreated (Control; n = 101). In both groups, 1,667 iu of hCG was given IV when an ovarian follicle ≥35 mm was detected (in conjunction with estrous behavior) and each mare was bred by natural service. Treated mares were served earlier in the breeding season (mean ± SD interval to first service was 13.9 ± 3.0 vs 26.7 ± 13.2 d for Treated and Control groups, respectively; P < 0.001). In the Treated and Control groups, 95.2 and 42.6% of mares were served within the first 21 d of the season (P < 0.001). Treated mares conceived earlier in the breeding season (mean number of days to conception 37.5 ± 14.2 vs 50.8 ± 21.3 d, P = 0.01). There was no difference between groups in the first service pregnancy rates (53.9 and 50.5% for Treated and Control mares, P = 0.89). Treatment with an intravaginal device increased the number of mares conceiving by the end of the breeding season (91.3 vs 82.3% for Treated and Control groups, P = 0.04). Therefore, this treatment protocol appeared to offer a convenient, economical and reliable method for managing transitional mares on commercial Thoroughbred stud farms.     

Exposure to stallion accelerates the onset of mares' cyclicity

Horses (Equus caballus) belong to the group of seasonally polyestrous mammals. Estrous cycles typically start with increasing daylight length after winter, but mares can differ greatly in the timing of onset of regular estrus cycles. Here, we test whether spatial proximity to a stallion also plays a role. Twenty-two anestrous mares were either exposed to one of two stallions (without direct physical contact) or not exposed (controls) under experimental conditions during two consecutive springs (February to April). Ovarian activity was monitored via transrectal ultrasound and stallion's direct contact time with each mare was determined three times per week for one hour each. We found that mares exposed to a stallion ovulated earlier and more often during the observational period than mares that were not exposed to stallions. Neither stallion identity nor direct contact time, mare age, body condition, size of her largest follicle at the onset of the experiment, or parasite burden significantly affected the onset of cyclicity. In conclusion, the timing of estrous cycles and cycle frequency, i.e., crucial aspects of female reproductive strategy, strongly depend on how the mares perceive their social environment. Exposing mares to the proximity of a stallion can therefore be an alternative to, for example, light programs or elaborated hormonal therapies to start the breeding season earlier and increase the number of estrous cycles in horses.     

Factors influencing conception rates of Arab mares in Tunisia

In order to investigate the factors affecting the reproduction efficiency of Arab breeding mares in Tunisia, breeding data corresponding to 2340 mated cycles, over 5 years (from 2000 to 2004), from 555 mares offspring of 50 sires and bred with 17 stallions were analysed using a multivariate logistic regression. We chose logit link function and binomial distribution and we used log-likelihood-ratio (LL) and Wald tests (X² Wald) to test the mean values. The factors of variation included in the model were the year, the stallion, the age of the mare at mating, the sire and the category of the mare. Logistic regression results showed that age and sire affected both the overall conception rate and the first-cycle conception rate of the mares whilst category and stallion influenced only the overall conception rate. To our knowledge, this is the first study showing that the sire of the mare can affect both the first-cycle conception rate and the overall conception rate of the mares.     

Epidemiologic aspects of Taylorella equigenitalis

Contagious equine metritis (CEM) is a sexually transmissible disease in mares. Although the disease is commonly diagnosed by culturing the causative bacterium Taylorella equigenitalis (T. equigenitalis) . false negative results do occur. A recently developed Polymerase Chain Reaction (PCR) assay, however, appeared to be much more sensitive, with initial results indicating an unexpected high incidence of the agent in selected horses. In this study, samples from 107 randomly selected mares with no clinical signs of CEM submitted for conventional culture were all negative for T. equigenitalis . but in the PCR-assay 54 (49%) were positive for Taylorella -DNA. Positives in the PCR-assay were found in all breeds tested, even in horses imported from the isolated population in Iceland. These findings suggest that T. equigenitalis was present long before it was first isolated in 1977, The high incidence of Taylorella in horse populations without apparent clinical signs of CEM, the occurrence of incidental clinical case and the known variability between strains, all indicate that Taylorella is endemic in the horse population. In order to explore whether the organism is present in species other than the horse, we also used the PCR-assay on clinically health donkeys (n = 14), zebras (n = 15), Przewalski horses (n = 2) and cows (n = 21). All the animals showed negative results except one of the Przewalski horses, and one cow that was repeatedly found to give positive reaction. We also found that the fertility of 7 stallions with cultures positive for Taylorella (6 used in an AI-program and 1 by natural breeding) was not affected, as shown by the normal range of foaling rates in mares inseminated or bred by these stallions. The overall results may be interpreted to mean that Taylorella is of limited significance in horse breeding.