Breeding Stallions Research Articles

Adição de alanina, glicina e glutamina ao meio crioprotetor seminal de garanhões Mangalarga Marchador

Objetivou-se neste trabalho verificar o efeito da adição de alanina, glicina e glutamina ao meio crioprotetor seminal de garanhões Mangalarga Marchador. Foram utilizados cinco garanhões provenientes do haras Lugavi. Três ejaculados de cada garanhão, após coleta e avaliação, foram divididos em seis tratamentos: sem adição de aminoácidos, adição de 40 mM de alanina, adição de 40 mM de glicina, adição de 60 mM de glutamina, adição de 7 mM de alanina + 7 mM de glicina + 20 mM de glutamina e adição de 40 mM de alanina + 40 mM de glicina + 60 mM de glutamina ao diluente de congelamento convencional. Foram avaliados os parâmetros motilidade total, motilidade progressiva, retidão, linearidade, velocidade média do percurso, velocidade linear, velocidade curvilínea, amplitude lateral de cabeça e frequência de batimentos dos espermatozoides por meio de análise espermática assistida por computador (CASA), funcionalidade da membrana plasmática por choque hiposmótico e integridade de membrana acrossomal pelo teste FITC-PSA. Não houve melhora nos parâmetros de motilidade e cinética espermática nem na funcionalidade de membrana, entretanto, a adição de aminoácidos ao meio crioprotetor seminal aumentou o número de espermatozoides com membrana acrossomal íntegra. Os melhores resultados neste teste são obtidos com 40 mM de alanina (78,6 ± 13,6), 40 mM de glicina (74,7 ± 19,6) ou 7 mM de alanina + 7 mM de glicina + 20 mM de glutamina (76,8 ± 17,5), porém outros estudos devem ser realizados para determinação da concentração ideal desses componentes.

Review on Effects of Fescue Grass Ergot Alkaloids in the Horse and Preliminary Study on Effect of Fescue Grass Ergot Alkaloid in the Stallion

Feed with ergot alkaloids ingested by horses has a deleterious clinical and economic impact on the industry. The clinical manifestation of the effects in mares is early embryonic mortality, abortions, prolonged gestation, dystocia, thickened (edematous) or retained placental membranes, agalactia, and increased rates of newborn mortality. For the stallion, very little is known, although ergot alkaloids decrease the ejaculate volume. However, a large number of breeding stallions graze endophyte infected (E+) pastures. This is especially true in the southeastern United States, and clinically we do not perceive that any stallions have any defined problems that could be attributed to ergot alkaloids. However, the number of spermatozoa produced by any stallion might mask the effects. The effects on fertility may be more subtle and only evident with sperm cell manipulation such as chilling or freezing. A preliminary study was performed on six breeding stallions fed feed containing infected fescue seed. We were not able to determine any significant ( P < .05) detrimental effects on sperm motility, number morphology, and sperm morphology when compared with controls.

Characteristic of selected rheological parameters of stallion ejaculate

Abstract. Dynamic viscosity of native (30 minutes after ejaculation) and 24 hours stored (at 4 °C) stallion ejaculate was measured. The ejaculate from 10 breeding stallions was examined in three different experimental series. The average value of dynamic viscosity at shear rate 1.02 s−1 was found to be 416.8 ± 10.1 mPa.s. The correlation between ejaculate volume, sperm concentration and viscosity was tested. The experiments resulted in finding a dependence between increasing viscosity and decreasing sperm concentration (rp = −0.67; P&lt;0.05). Performed experiments with changing shear rate demonstrated non-Newtonian characteristics of stallion ejaculate with a clear shear-thinning behaviour. Stallion ejaculate appeared to be slightly time-dependent liquid.

Sperm morphology and chromatin integrity in Swedish warmblood stallions and their relationship to pregnancy rates

BackgroundArtificial insemination is not as widely used in horses as in other domestic species, such as dairy cattle and pigs, partly because of the wide variation in sperm quality between stallion ejaculates and partly due to decreased fertility following the use of cooled transported spermatozoa. Furthermore, predictive tests for sperm fertilising ability are lacking. The objective of the present study was to assess sperm morphology and chromatin integrity in ejaculates obtained from 11 warmblood breeding stallions in Sweden, and to evaluate the relationship of these parameters to pregnancy rates to investigate the possibility of using these tests predictively.MethodsAliquots from fortyone ejaculates, obtained as part of the normal semen collection schedule at the Swedish National Stud, were used for morphological analysis by light microscopy, whereas thirtyseven were used for chromatin analysis (SCSA) by flow cytometry. The outcome of inseminations using these ejaculates was made available later in the same year.ResultsRanges for the different parameters were as follows; normal morphology, 27–79.5%; DNA-fragmentation index (DFI), 4.8–19.0%; standard deviation of DNA fragmentation index (SD_DFI) 41.5–98.9, and mean of DNA fragmentation index (mean_DFI), 267.7–319.5. There was considerable variation among stallions, which was statistically significant for all these parameters except for mean_DFI (P < 0.001, P < 0.01, P < 0.001 and P < 0.2 respectively). There was a negative relationship between normal morphology and DFI (P < 0.05), between normal morphology and SD_DFI (P < 0.001), and between normal morphology and mean_DFI (P < 0.05). For specific defects, there was a direct relationship between the incidence of pear-shaped sperm heads and DFI (P < 0.05), and also nuclear pouches and DFI (P < 0.001), indicating that either morphological analysis or chromatin analysis was able to identify abnormalities in spermiogenesis that could compromise DNA-integrity. A positive relationship was found between normal morphology and pregnancy rate following insemination (r = 0.789; P < 0.01) and a negative relationship existed between DFI and pregnancy rate (r = -0.63; P < 0.05). Sperm motility, assessed subjectively, was not related to conception rate.ConclusionEither or both of the parameters, sperm morphology and sperm chromatin integrity, seem to be useful in predicting the fertilising ability of stallion ejaculates, particularly in determining cases of sub-fertility.

A cross-sectional survey of Thoroughbred stud farm management in the North Island of New Zealand

AIM: To obtain initial baseline data on the management of Thoroughbred stud farms in the North Island of New Zealand. METHODS: Data on the management of Thoroughbred stud farms were collected from a sample of 22 stud farms located in the south Auckland/Waikato region (n=15) and lower North Island (n=7) of New Zealand, using a face-to-face survey. The studmaster provided information on the size, scope and management of the farms during the 2004/2005 breeding season. Analysis was based on the location of the farm and size of the breeding operation (number of resident mares). RESULTS: Effective farm size ranged from 20 to 526 ha and averaged 167 (standard error (SE) 36) and 88 (SE 49) ha in the south Auckland/Waikato and lower North Island areas, respectively. Some farms in the Auckland/Waikato region stood shuttle stallions. The median number of stallions per farm was three (range 0.9), and the median mare-to-stallion ratio was 43 (range 10.250). The farms had a mean of 50 (range 7.180) wet mares and 21 (range 0.100) dry mares. The number of mares per breeding stallion increased with increasing size of breeding operation (p=0.04), being 28 (95% confidence interval (CI) = 10.56) vs 40 (95% CI=16.74) vs 74 (95% CI=44.113) for moderate (≤70 mares), medium (90–199 mares) and large (≥200 mares in total) operations, respectively. Seventy-one percent of farms aimed to breed dry mares early in the breeding season, and used a combination of lights, hormone therapy, and rising plane of nutrition to achieve this. Foaling took place in foaling paddocks monitored using a night foaling attendant (17/22) or with foaling alarms (5/22). At birth, 17/22 studmasters routinely administered antibiotics, 14/22 administered tetanus antitoxin, 9/22 administered an enema to foals, and 2/22 did not routinely administer prophylactic treatments. Weaning occurred at 5 (range 3.7–7) months of age, and foals were confined to a box for 1–2 weeks on 16/22 farms. Weaned foals were drenched with anthelmintics every 7 (range 4–9) weeks, and were fed 2.9 (range 1–6) kg of concentrate feed while at pasture until intensive management associated with preparation of the horses for auction began 13 (range 6–20) weeks before the yearling sales. Eight farms weighed the weanlings, at least monthly, to monitor growth. CONCLUSIONS AND CLINICAL RELEVANCE: The management of Thoroughbred horses was relatively consistent throughout the regions surveyed. Utilisation of breeding stallions tended to be more efficient on the larger stud farms in the south Auckland/Waikato region. Even though foals are grown at pasture they are often provided with large quantities of concentrate feed.

A polymorphism within the equine CRISP3 gene is associated with stallion fertility in Hanoverian warmblood horses

Fertility of stallions is of high economic importance, especially for large breeding organisations and studs. Breeding schemes with respect to fertility traits and selection of stallions at an early stage may be improved by including molecular genetic markers associated with traits. The genes coding for equine cysteine-rich secretory proteins (CRISPs) are promising candidate genes because previous studies have shown that CRISPs play a role in the fertilising ability of male animals. We have previously characterised the three equine CRISP genes and identified a non-synonymous polymorphism in the CRISP1 gene. In this study, we report one non-synonymous polymorphism in the CRISP2 gene and four non-synonymous polymorphisms in the CRISP3 gene. All six CRISP polymorphisms were genotyped in 107 Hanoverian breeding stallions. Insemination records of stallions were used to analyse the association between CRISP polymorphisms and fertility traits. Three statistical models were used to evaluate the influence of single mutations, genotypes and haplotypes of the polymorphisms. The CRISP3 AJ459965:c.+622G>A SNP leading to the amino acid substitution E208K was significantly associated with the fertility of stallions. Stallions heterozygous for the CRISP3 c.+622G>A SNP had lower fertility than homozygous stallions (P = 0.0234). The pregnancy rate per cycle in these stallions was estimated to be approximately 7% lower than in stallions homozygous at this position.

Expression and bioactivity of a single chain recombinant equine luteinizing hormone (reLH)

To study structure–activity relationships and the role of equine gonadotropins in the normal and pathophysiology of equine reproduction, the availability of purified hormones is essential. Previous expression studies in transfected CHO cells showed inefficient assembly of the human and bovine α and β subunits, resulting in low levels of recombinant LH. The ability to express a single chain bearing genetically linked α and β subunits bypasses this rate-limiting assembly step. A chimera was constructed by overlap PCR in which the carboxy terminal end of the eLHβ subunit was genetically fused to the amino end of the α subunit. This gene was transfected into CHO cells and the recombinant product was purified through multiple steps, including a Fractogel resin separation. Serial dilutions of pituitary derived native eLH and the single chain reLH were compared in an eLH radioimmunoassay (RIA); the concentration curves between the single chain recombinant eLH and the native eLH standard were parallel. The biological activity of the analog was determined in vitro and in vivo using homologous equine models. Testicular tissue from five colts was processed for Leydig cell cultures. Increasing doses of reLH were incubated with equine Leydig cells for 24 h in vitro and testosterone production was determined by RIA. Recombinant eLH stimulated a greater than 15-fold increase in testosterone production in a dose-dependent manner. Quarter Horse breeding stallions were treated with either reLH ( n = 5) or saline ( n = 3) and plasma testosterone concentrations were measured by RIA. Recombinant eLH stimulated a four-fold increase in circulating testosterone concentrations compared to the saline control. Therefore, the single chain recombinant will be effective for a variety of structure–function analyses and for breeding management in the horse.

Developments in European Horse Breeding and Consequences for Veterinarians in Equine Reproduction

The liberalization of European animal breeding legislation and an increasing diversity of equestrian sports have led to a constant rise in the number of horse breeds and breed registries. In addition to the trend towards more and smaller breed registries, there is another trend towards an international expansion of the bigger established sport horse breeds. Regional breeds, at least in smaller countries, may no longer be able to run an independent breeding programme. The typical horse breeder, in the future, will be a female and qualified in equestrian sports. Artificial insemination (AI) mainly with fresh or cooled-transported semen has become a major breeding tool, allowing breeders all over Europe to benefit from the best stallions of most breeds. New AI techniques such as low-dose insemination may remain restricted to individual stallions and also the interest of breeding programmes in sex determination of foals via semen sorting is limited. Embryo transfer and associated techniques, although allowed by most breeds, have not contributed significantly to genetic progress in European sport horses so far. A potential use of cloning may be to produce gonad-intact copies from geldings that have performed to a superior level. With a more open and international structure of horse breeding and increased use of AI, equine reproduction and biotechnology should be emphasized by veterinary curricula and continuing professional education programmes.

Can early training of show jumpers bias outcome of selection events?

Abstract Evaluation of free jumping at sub-maximal heights is common practice within selection procedures for young breeding stallions. Early training might cause an unjustified bias. To investigate this, data from a 5-year longitudinal study on 30 horses were used. Half of these horses (experimental group) had received early training between 6 months and 4 years, the other half (control group) had not. Between 4 and 5 years, all horses had received standard training under saddle. At the age of 5 years, the horses were tested in a puissance competition and the 7 best and 6 worst jumpers were used for the present study. Kinematic variables that were different at ages 5 years and 6 months, and had been shown to be predictive for performance in earlier studies, were analysed at the age of 4 years. It showed that early training had effaced the differences between potentially good and less good show jumpers in 3 of 3 predictive variables and had introduced a (false, because not related to performance) difference between the trained and untrained horses in one of them and a nearly significant trend in another. Early training may to a certain extent obscure differences in talent among individuals at the age at which selection events occur. Experienced judges may be able to account for this, but studbooks and judges should be aware of this possible pitfall.

Sperm morphology in Estonian and Tori Breed Stallions

The standard procedure for assessing the breeding potential of a stallion includes the parameter total number of spermatozoa classified as morphologically normal. This study investigated sperm morphology of fresh semen in randomly chosen Estonian (E, n = 8) and Tori (T, n = 7) breed stallions with proven fertility. Two ejaculates were examined from each stallion. An aliquot from each ejaculate was fixed in 1 mL formol-saline immediately after collection and examined with phase-contrast microscope at a magnification 1000× for all types of morphological abnormalities. Furthermore smears were prepared and stained according to Williams (carbolfuchsin-eosin) for a more detailed examination of the sperm heads with light microscope at a magnification 1000×. Analysis of variance was applied to the data, and results are presented as LSmeans (± SE). One T stallion that had a disturbance in the spermatogenesis and one 22-year-old E stallion were not included in the analyses. The T stallions had on average 57.5 ± 4.1% and the E-stallions 74.4 ± 3.8% morphologically normal spermatozoa (p = 0.012). In 4 of 7 T stallions and 7 of 8 E stallions both ejaculates had >50% morphologically normal spermatozoa. There was a significant difference between breeds in mean percentage of proximal droplets (17.3 ± 2.7% and 2.9 ± 2.5% for T and E stallions, respectively; p = 0.003).

109REFREEZING STALLION SPERMATOZOA FOR ASSISTED REPRODUCTION

Equine semen is commonly frozen in 0.5-mL straws at a concentration of 400 million spermatozoa per mL. Equine pregnancies have been produced in the past few years using assisted reproduction techniques that require very few sperm, such as sperm injection and gamete intrafallopian transfer. Consequently, thawing even a single straw would waste a high percentage of the sperm. The goals of this study were to: (1) evaluate the motility and viability of cryopreserved spermatozoa that had been thawed and refrozen, and (2) compare the effect of serial dilution on refreezing parameters. It was hypothesized that both motility and viability would be significantly decreased as a consequence of refreezing, but sufficient live, motile spermatozoa would be present for assisted reproductive techniques. Semen from six stallions of mixed light horse breeds was collected, evaluated, and frozen in lactose-EDTA in 0.5-mL straws. Semen from each stallion was subsequently thawed, held at room temperature for 10 minutes, and then refrozen in 0.25-mL straws. Additional semen from the initial freeze was thawed, diluted in the original extender, and refrozen at concentrations of 40×106, 4×106, 4× 105, and 4×104 spermatozoa per mL. Refrozen semen was evaluated for motility visually and by CASA. Viability of refrozen semen was determined by flow cytometry following staining with propidium iodide (PI). Percentages of motile spermatozoa prior to freezing, after the first freezing, and after the second freezing were compared using the PROC GLM model in SAS. All values are presented as the mean±standard deviation. Total motility decreased sigificantly (P&amp;lt;0.05) from 91.8±3.1% prior to freezing to 64.2±7.7% after the first freezing and 45.7±10.4% after the second freezing. However, only a tendency (P=0.09) toward a decrease in sperm viability following refreezing as measured by PI staining was noted. Dilution of sperm prior to refreezing did not significantly effect (P&amp;gt;0.05) subsequent motility or viability parameters. This study demonstrated that refrozen equine semen retained approximately 70% of the initial post-thaw motility. Dilution prior to refreezing would allow for the reallocation of a single 0.5-mL straw into hundreds or thousands of smaller straws for future use in assisted reproduction. Refreezing would allow for the judicious use of valuable stallion semen in limited supply.

Testicular measurements and daily sperm output of Tori and Estonian breed stallions.

Evaluation of testicular measurements and daily sperm output (DSO) yields valuable information for predicting the reproductive capacity of stallions. The present study evaluated testicular measurements (height, length, width and circumference) and DSO of eight Tori and eight Estonian breed stallions. One ejaculate of semen was collected daily for 10 subsequent days from each stallion. The gel-free volume of semen was measured with a graduated glass cylinder and the sperm concentration was assessed with a Chorjajev chamber. The volume of gel-free fraction was multiplied by the sperm concentration to give the total number of spermatozoa (TSN). The DSO was calculated as mean TSN of collection on days 8-10 in Tori breed stallions and on days 4-10 in Estonian breed stallions. The DSO of Tori breed stallions was 12.9 x 109 spermatozoa and of Estonian breed stallions 4.5 x 109 spermatozoa (p < 0.001). Testicular measurements (in cm) 1 day after the last semen collection were as follows: left testis- height 7.3, length 10.4 and width 7.3 in Tori breed stallions, and 5.9, 8.1 and 5.9, respectively, in Estonian breed stallions; right testis- height 7.4, length 10.6 and width 7.4 in Tori breed stallions, and 5.5, 7.4 and 5.3, respectively, in Estonian breed stallions. All these testicular measurements were significantly smaller in Estonian than in Tori breed stallions (p < 0.001). Testicular circumference was 45.4 and 35.4 cm in Tori and Estonian breed stallions, respectively (p < 0.001). The testicular circumference was correlated with DSO in both Estonian (p < 0.05) and Tori breed stallions (p = 0.071). The results give us valuable information on the reproductive capacity of Tori and Estonian breed stallions.

Evaluation of cryopreserved stallion semen from Tori and Estonian breeds using CASA and flow cytometry

Methods to evaluate the quality of frozen-thawed stallion semen are still needed, particularly those considering the sperm function. The present study evaluated sperm motility, membrane and acrosome integrity and the capacitation status of frozen-thawed spermatozoa from seven Tori and six Estonian breed stallions by way of computer assisted sperm analysis (CASA), a triple fluorophore stain combination and Merocyanine 540, respectively, the latter ones using flow cytometry. Two ejaculates from each stallion were cryopreserved using the Hannover method in 0.5 ml plastic straws. Two straws per ejaculate per stallion were thawed at 37 °C for 30 s. Motility was analysed with CASA immediately after thawing, while for flow cytometry spermatozoa were cleansed by 70:40% Percoll discontinuous density gradient separation before analysed for sperm viability, acrosome integrity (stained with SNARF, PI and FITC-PSA) and capacitation status (stained with Merocyanine 540/Yo-Pro-1). Results (as least square means) were as follows: the motility of frozen-thawed semen was 43.4% for Tori stallions and 42.3% for Estonian stallions ( P>0.05). After Percoll separation 79.3% of the spermatozoa from Tori stallions had intact acrosomes and 1.7% of them showed early signs of capacitation. The same parameters for Estonian stallions were 84.5 and 2.3%, respectively. There were no statistically significant differences between breeds or ejaculates within breed for any evaluated parameter. We conclude that triple staining and flow cytometry are valuable techniques to evaluate frozen-thawed stallion spermatozoa, and that no differences in quality of frozen semen were registered between Tori and Estonian breed stallions, allowing implementation of this technology in the Estonian horse population.

Cytological identification and quantification of testicular cell types using fine needle aspiration in horses.

Fifteen stallions of different breeds, age 3-11 years, had their right testicles evaluated by fine needle aspiration cytology (FNAC). Cytological analysis showed the following spermatogenic cell types: spermatogonia (1.6% +/- 1.1); spermatocyte I (3.4% +/- 2.2); spermatocyte II (0.8% +/- 0.7); early spermatids (25.5% +/- 9.5); late spermatids (37.0% +/- 9.3). Spermatozoal numbers were expressed as the spermatic index (SI = 31.5% +/- 8.5) and Sertoli cells were expressed as the Sertoli cell index (SEI = 20.9% +/- 17.0) (means +/- s.d). Identification of cell types was relatively easy and no immediate adverse effects of aspiration were noted. The results suggest that FNAC of testis may assist clinical diagnosis in the study of male equine infertility.

Sexual Activity Influences the Secretion of Reproductive Hormones in the Stallion

ContentsThe aim of this study was to investigate the effect of sexual activity on concentrations of reproductive hormones in plasma of stallions. In the first experiment, two groups of stallions were monitored for secretion of luteinizing hormone (LH), testosterone and oestradiol from the beginning until shortly after the end of the breeding season. One group of animals were reserve stallions not used for breeding (group 1, n = 10), the other group consisted of active breeding sires (group 2, n = 8). Blood samples were withdrawn from March to August at 14‐day intervals. In sexually nonactive stallions (group 1), seasonal variations in LH, testosterone and oestradiol occurred and concentrations of these hormones reached a maximum in May (p &lt; 0.05). In the breeding stallions (group 2), no significant changes in the concentrations of these hormones were found between March and August. Concentrations of LH and testosterone were significantly lower in breeding stallions than in reserve stallions at most blood sampling times (p &lt; 0.05). In the reserve stallions, oestradiol concentrations were significantly higher than in the breeding stallions in April and in June (p &lt; 0.05). In a second experiment, the effect of regular sexual activity (semen collection three times per week) on the concentration of LH, testosterone and oestradiol was tested in a group of breeding stallions after a period of sexual rest for several weeks. Blood samples were taken once daily starting the day before the first semen collection was performed. Testosterone concentration significantly decreased in the first days after semen collection started (p &lt; 0.05), while LH secretion was only transiently decreased and no effects on oestradiol concentration were found. In both experiments, semen parameters were within the normal range of fertile stallions. No correlations between the sexual drive of the stallions and concentration of reproductive hormones occurred. It can be concluded that in the stallion the secretion of reproductive hormones is influenced by sexual activity. Regular semen collection seems to inhibit testosterone release by unknown mechanisms while the effects on LH and oestradiol secretion are less pronounced.

Reproductive parameters of miniature stallions

Breeding soundness evaluation (BSE) of stallions is a routine component of stud farm practice. Guidelines for assessing satisfactory breeding potential have been developed using data derived from stallions of full-size breeds. In view of the increasing popularity of miniature stallions, knowledge of normal semen parameters of these stallions is important. Therefore, testicular measurements and semen parameters from 216 sexually rested miniature stallions were obtained. Semen was collected twice, 1.5 to 3 h apart, using an artificial vagina. Values were averaged over the 2 collections because of the sexual inexperience of the stallions. The smaller stallions (Group A, 72 to 86 cm; Group B, 87 to 96 cm) had smaller testicles (P<0.05), and Group A stallions had the lowest ejaculate volume (P<0.05) compared with Group C (97 to 104 cm) stallions. Thus, although there was no difference in the concentration of spermatozoa per milliliter between groups of stallions, Group A stallions had fewer total spermatozoa in their ejaculate than Group C stallions (4.31 ± 0.47 × 10 9 vs. 5.41 ± 0.30 × 10 9, P<0.05). Moreover, miniature stallions had smaller testicles and fewer total spermatozoa in their ejaculate than is commonly accepted as normal in full-size stallions. Average total scrotal width of miniature stallions was found to be 7.13, 7.38 and 7.95 cm for Groups A, B and C, respectively. The average total number of spermatozoa in the ejaculates of miniature stallions in this study was 4.94 ±0.22 × 10 9 cells, with 1.75 ± 0.09 × 10 9 total normal, motile spermatozoa. When only stallions <96.5 cm in height were considered (conforming to requirements of the American Miniature Horse Association Registry), the average total number of spermatozoa in the ejaculates was 4.59 ± 0.30 × 10 9 cells, with 1.70 ± 0.11 × 10 9 total normal, motile spermatozoa. Based on these findings, different criteria should be used to evaluate the potential breeding soundness of miniature stallions than are commonly applied to full-size stallions.

Bachelor and Harem Stallion Behavior and Endocrinology1

Horses naturally breed within a harem social unit that typically includes one mature breeding stallion with several mares and their immature offspring. Non-harem stallions comprise relatively stable social groups known as bachelor bands. When a harem position becomes vacant, a stallion emerges from a bachelor band to fill the vacancy. We studied harem and bachelor stallion phenomena using a model of pony stallions pastured together under semi-feral conditions. In this model, one stallion assumed the role of “harem stallion,” vigilantly guarding an area within the stallion pasture along the fence line facing nearby mare pastures. The remaining stallions interacted as a bachelor band. If the harem stallion was removed from the pasture, a stallion from the bachelor group rapidly emerged to fill the position. If we replaced to the pasture a former harem stallion, the former harem stallion typically displaced the incumbent harem stallion back to the bachelor band. Order of emergence from the bachelor band to fill harem position vacancies, while highly repeatable, was not strongly associated with bachelor age, height, weight, testosterone concentrations, ranked level of aggressive behavior, or ranked leader-follower behavior. Emergence from bachelor to harem status consistently resulted in a sudden sharp rise in testosterone concentration, which remained high for the duration of harem status. Displacement from harem status back to the bachelor band was consistently associated with a sharp decrease in testosterone concentration. Testosterone concentrations with harem status were significantly higher than those with bachelor status for all months of the year. These changes in behavior and testosterone concentrations of sexually experienced mature stallions suggest social modulation of behavior and endocrinology, with enhancement of reproductive function as a harem stallion and/or suppression as a bachelor. Extremely wide variation in testosterone concentrations due to sociosexual conditions raises important questions about basic neuroendocrinology of stallions, including methodological concerns. Equally significant are questions raised regarding management of domestic breeding stallions.

Effects of a 3 month endurance training programme on skeletal muscle histochemistry in Andalusian, Arabian and Anglo-Arabian horses.

Twenty adult (5 to 14 years old) sedentary stallions of several breeds (8 Andalusians, 7 Arabians and 5 Anglo-Arabians) were endurance-trained for 3 months. Duplicate biopsies from 2 different depths (20 mm, superficial sampling site; 60 mm, deep sampling site) of the gluteus medius muscle were collected before and after training and after 3 months of detraining. Few significant changes in muscle fibre type composition were recorded in response to training. The percentage of type I fibres in the deep sampling site of the muscle in Andalusian horses and of type IIB oxidative fibres in the superficial region in Anglo-Arabians had increased significantly (P < 0.05) after training. The mean type I and IIA cross-sectional area was increased significantly (range P < 0.05 to P < 0.01) after 3 months' training in the deep site of the muscle in Arabian and Andalusian horses, but not in Anglo-Arabians. The changes seen in fibre sizes disappeared after the detraining period. The mean number of capillaries adjacent to type I fibres in the superficial sampling site of the muscle had increased significantly (P < 0.05) in response to training in Andalusian and Arabian horses. However, a significant decrease in the mean number of capillaries in contact with each fibre type relative to the mean area of that fibre type was observed associated with training in the deep region of the muscle for type I and IIA fibres in Arabians (P < 0.01) and for type I fibres in Andalusian horses (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Alternative selection strategies for performance of the Swedish warmblood horse

The Swedish riding horse population includes about 6000 broodmares and 150 breeding stallions. The overall breeding goal is to produce riding horses competitive in several disciplines, i.e. dressage as well as showjumping and eventing. The effectiveness of this multi-purpose objective was studied in alternative strategies for selecting stallions and mares as candidate dams for them. The alternative selection strategies for stallions included 1-stage (conformation), 2-stage (conformation and performance test) and 3-stage (conformation, performance test and competition results at advanced levels) selection schemes. The mare selection schemes included the corresponding 1- and 2-stage selection schemes. The results clearly showed the 2-stage selection procedure to be most efficient, especially for stallions. It is important that the intensity in selection after the performance test is kept high. Differences in defining the breeding objective are less important, provided the selection is based on a performance test including both dressage and jumping. According to the results, the development of the Swedish performance testing scheme, in which now only 30% of the tested stallions are selected for breeding, seems justified. In mare selection schemes, performance tests also seem to be justified, especially if jumping ability is to be improved. Differences between field and station tests are only minor and since the volume of testing can be much higher in the field this would allow a much stronger selection and should thus be preferred.

Imipramine-induced erection, masturbation, and ejaculation in male horses

Imipramine hydrochloride was administered to five male horses (400–500 kg b.wt.): one inexperienced young stallion, two mature normal breeding stallions, one 5-year-old stallion with erection and ejaculatory dysfunction, and one long-term castrated male horse. Oral imipramine treatment (100 to 600 mg, twice daily) led to frequent erection and masturbation while at rest in the stall in a nonsexual context. Intravenous imipramine treatment over a range of doses (50 to 1000 mg) similarly induced erection and masturbation in all animals. Erection typically occurred within 10 minutes after injection, and erection masturbation continued intermittently for 1 to 2 hours. These erections proceeded as during sexual excitement to a normal firmness and eventual engorgement of the glans penis. Two stallions ejaculated while masturbating. Mild ataxia and drowsiness appeared at the higher doses, but the animals remained responsive to auditory, visual, and tactile stimuli. Erection and masturbation were often interrupted by activities about the barn or the approach of the handler, suggesting cortical inhibitory control of the erection. When tested in a sexual context immediately following IV treatment (500 mg), the two mature breeding stallions bred normally. The 5-year-old stallion, which had not ejaculated over several months of breeding attempts, spontaneously ejaculated following IV imipramine treatment. Subsequently, this stallion has ejaculated during copulation while on low dose oral (100 mg, twice daily) imipramine treatment. Plasma total androgens increased during treatment in these stallions. The long-term castrate showed erection and masturbation following IV imipramine treatment, suggesting that the effect of imipramine is not testosterone dependent.