Hormone therapy for control of reproduction in mares and stallions

Because the reproductive performance of mares is lower than that of any other domesticated species, hormone therapy is important in ensuring fertility and proper management of pregnancy. Current techniques of hormone therapy are discussed.     

High prevalence of mycoplasmas in the genital tract of asymptomatic stallions in Austria

Mycoplasma equigenitalium and M. subdolum have been implicated in genital disorders and infertility of horses. The reported cytopathic effects of M. equigenitalium observed in vitro underscore its potential pathogenic role in reproductive dysfunction in mares. This study was initiated to determine the prevalence of mycoplasmas in the genital tract of stallions in relationship to age, clinical signs, geographic location and semen quality. For this purpose the mycoplasma flora of the genital tract of 116 stallions of the Noric breed was determined by isolation and colony immunoblotting and by polymerase chain reaction (PCR) assays. Of 438 swabs from the genital tract, pre-ejaculatory fluid and semen samples, 352 (80%) samples were positive by PCR and 125 (29%) were positive by culture. Mycoplasmas were isolated predominantly from the fossa glandis and urethra and less frequently from the penis shaft and from semen. M. equigenitalium (89 isolates) and M. subdolum (70 isolates) were the predominant species identified. M. equirhinis and M. felis were detected in 27 and 8 samples, respectively. Comparison of these isolations with clinical signs, semen quality, and age of the stallions revealed no significant correlation. However, geographical location of the stallion significantly correlated with mycoplasma detection. These results suggest that mycoplasmas are present as commensals in the genital tract of stallions. Thus, clinically healthy stallions may present a permanent reservoir for infection of mares via venereal transmission.     

The effect of the age of stallions and mares on their fertility

The study was based on the documentation of the Napajedla Stud Farm of the English Thoroughbred horse for 1888-1972. Evaluating the effect of the age of stallions on their fertility (leaving aside the variability of the age of their mothers), such an effect was found to be significant only in four out of the 26 studs evaluated. In 65% of the selected stallions, the correlation coefficients were found to be negative, but without statistical significance. However, the objective of the study was to evaluate stallions and mares parallelly as to their age variability and fertility. The relationships of the effect of the age of the stallion and of the mare on fertility were evaluated by different modificatons of the value chi2. The prerequisite for the analyses of the effect of different stallion age at a constant age of mares was the calculation of the global chi2 used jointly for the evaluation of the variable age of stallions and mares. The result are varied and report on the individuality of the effect of stallions, giving no clear basis for generalizing any fertility-decreasing tendency with the higher age of the parents. The problem is analyzed from the physiological viewpoint.     

Anti-oxidative status and semen quality during cooled storage in stallions

Activity of the anti-oxidative enzymes glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and catalase (CAT), content of thiobarbituric acid reactive substances (TBARS) and SH-groups were determined in native stallion semen (n = 8 stallions). Semen was then diluted in Kenney extender, EquiPro((R)) extender either with or without addition of N-acetyl cysteine or phosphate-buffered saline (PBS) and stored for 72 h at 5 degrees C. Correlations between initial activity of enzymes and development of semen motility and membrane integrity were calculated. Activities of GSH-Px, SOD and CAT immediately after semen collections were 10.0 +/- 0.6 picokatals, 0.40 +/- 0.03 SOD units and 0.70 +/- 0.05 nanokatals/10(6) spermatozoa respectively. TBARS content was 0.06 +/- 0.01 nmol and SH-group content 1.7 +/- 0.5 mmol/10(6) spermatozoa. The loss of motile spermatozoa during storage did not differ between extenders. N-acetyl cysteine had no effect on semen motility and membrane integrity. The loss in membrane-intact spermatozoa was highest (P < 0.05) in semen diluted in PBS. Motility and membrane integrity after addition of extender were positively correlated with GSH-Px and CAT, indicating that anti-oxidative mechanisms contribute to the initial high percentage of motile and membrane-intact spermatozoa. However, in these samples the decrease in semen quality was most pronounced. No correlations existed between initial activity of anti-oxidative enzymes, peroxidation products and semen quality during storage. This indicates that once extender has been added, peroxidative damage to sperm membranes is not the predominant cause of losses in semen quality.     

Reproductive efficiency of Flatrace and National Hunt Thoroughbred mares and stallions in England

REASONS FOR PERFORMING STUDY: Previous surveys of reproductive efficiency in British Thoroughbreds included only mares and stallions standing on studfarms in and around Newmarket. The present study was widened to compare Flatrace (FR) (Group A) and National Hunt (NH) (Group B) mares and stallions on studfarms throughout England. OBJECTIVES: To assess the influences of mare type, status and age, and veterinary manipulations on reproductive efficiency parameters. To compare the inherent fertility of stallions, based on singleton and twin pregnancy rates and pregnancy loss rates, in Groups A and B Thoroughbred breeding stock. METHODS: Managers of 24 FR and 9 NH public studfarms were asked to complete a questionnaire for each mated oestrous cycle shown by 2321 Group A and 1052 Group B mares throughout the 2002 mating season. Parameters such as per cycle singleton and twin pregnancy rates, and pregnancy loss rates were noted, and the success of hormone treatments to induce oestrus and ovulation assessed. The number of matings per oestrus and per pregnancy were recorded, together with the incidence and effectiveness of uterine and other veterinary treatments. The inherent fertility of 84 Group A and 43 Group B stallions in the study, as measured by the singleton and twin early pregnancy rates and the pregnancy loss rates recorded in the mares they mated, was also estimated. RESULTS: Per cycle early pregnancy (Days 13-16) was 63.2% for Group A and 65.3% for Group B mares; and 10.3% and 13.1%, respectively, of those pregnancies were twins or triplets. Early, middle and late pregnancy loss rates were 7.2% vs. 8.0% (Days 15-42), 3.6% vs. 6.1% (Days 42-1st October) and 2.7% vs. 2.1% (October-foaling), respectively. Matings per oestrus and per early pregnancy were significantly higher in Group B vs. Group A mares. For stallions that mated > or = 30 mares, overall early pregnancy rates per cycle in mares mated ranged from 30-89% across the 2 groups. CONCLUSIONS: No major differences in reproductive efficiency were identified between FR and NH mares and stallions. Increasing mare age was the single biggest limiting factor to an otherwise high rate of fertility in well-managed English Thoroughbreds. POTENTIAL RELEVANCE: This study identified factors that influence reproductive efficiency in the Thoroughbred.     

Isolation of mycoplasmas from bovine semen in Northern Ireland

In a survey of 332 fresh and 137 processed bovine semen samples and 25 preputial washes, mycoplasmas and, or, ureaplasmas were isolated from 46 per cent, 31 per cent and 80 per cent, respectively. Intermittent isolation from different semen collections from the same bull indicated that at least three collections per bull were necessary to determine whether infection was present. When stored processed samples were examined Mycoplasma canadense and M bovigenitalium were isolated from straws taken as long ago as 1975. Addition of lincomycin and spectinomycin to the semen extender eliminated the isolation of mycoplasmas and reduced the rate of isolation of ureaplasmas.     

Persistent vaginal haemorrhage in five mares caused by varicose veins of the vaginal wall

Persistent bleeding from the vulva was the only presenting clinical sign in five non-pregnant pluriparous mares varying in age from eight to 20 years. These were two hunter types, one shire, one thoroughbred and one Arab pony. The haemorrhage originated from ulcerated varicose veins present on the dorsal wall of the vagina adjacent to the vestibulovaginal junction. All five mares were successfully treated, by submucosal resection (two), ligation of vessels (two) or diathermy (one). In four mares there was evidence of vulval incompetence caused by depression of the perineum. The importance of this and the role of impaired venous return during and after pregnancy are discussed.     

Effect of age on immunocytochemical staining characteristics of adenohypophyseal cells in Mongolian pony mares and stallions

OBJECTIVE: To determine the effect of age on immunocytochemical staining characteristics of adenohypophyseal cells of Mongolian pony mares and stallions. ANIMALS: 35 Mongolian ponies. PROCEDURE: Pituitary glands from 1- to 22-year-old horses of both sexes were collected at a commercial slaughterhouse in China and allocated into 7 groups according to age and sex: prepubertal stallions (n = 5; 1 to 2 years old), young stallions (6; 3 to 7 years old), middle-aged stallions (4; 10 to 12 years old), old stallions (5; 15 to 22 years old), young mares (3; 3 to 7 years old), middle-aged mares (5; 10 to 12 years old), and old mares (7; 15 to 22 years old). Pituitary glands were processed for microscopy, and sections were immunocytochemically stained for various pituitary hormones. The percentages and cell areas of 6 types of adenohypophyseal cells were determined by use of morphometry. RESULTS: Age-related alterations in adenohypophyseal cells were detected in horses > 15 years old. Percentage of somatotrophs decreased with age regardless of sex, and percentage of lactotrophs increased with age in stallions. In old mares, percentage of follicle-stimulating hormone cells increased, whereas cell area of follicle-stimulating hormone and luteinizing hormone cells decreased. Differences between sexes for percentage of somatotrophs and lactotrophs, and cell area of follicle-stimulating hormone and luteinizing hormone cells were not evident in old horses. CONCLUSIONS AND CLINICAL RELEVANCE: Differences among percentages and cell areas of pituitary cell types in old horses may be associated with degeneration of the sex organs.     

Thermoregulation of the testicle in response to exercise and subsequent effects on semen characteristics of stallions

Stallions (n = 8) were implanted with a thermal sensory device in the muscle of the neck and the subcutaneous tissue of the scrotum and then assigned to either a nonexercise (Non-EX; n = 4) or exercise (EX; n = 4) group. A motorized equine exerciser was used to work EX stallions 30 min/d for 4 d/wk during a 12-wk period from July through October 2010. Temperatures (subcutaneous scrotal, intramuscular neck, and rectal) were recorded at 0, 22, and 30 min after the start of exercise, as well as 60 and 120 min post-exercise. Hourly ambient temperature and relative humidity data were also obtained. Semen was collected at 0, 4, 8, and 12 wk and analyzed for volume, sperm concentration, total sperm numbers, percentages of total and progressively motile sperm, sperm morphologic characteristics, and sperm DNA quality. No effect (P > 0.05) of exercise was observed on any of the measured semen variables. Implantation of thermal sensory devices had no demonstrable acute or chronic effects on the scrotal or neck tissue, indicating that the thermal sensory devices are a safe and effective way to measure subcutaneous scrotal and neck temperatures. At 22 and 30 min of exercise, rectal and neck temperatures increased (P < 0.0001) approximately 1.9 and 2.4°C, respectively, and scrotal temperatures simultaneously increased, although not significantly (P = 0.33), approximately 0.8°C. Correlations existed between scrotal, neck, rectal, and ambient temperatures, with the correlation between scrotal and rectal temperatures being greatest (r(s) = 0.76; P < 0.0001). Although moderate exercise for a short duration in extreme heat and humidity did significantly increase core body temperatures in stallions, scrotal temperatures did not significantly increase, and sperm parameters were unaffected.