Modulating reproductive activity in stallions: A review

Limited association between stallion-like behavior and hormonal indicators of testicular remnants in geldings

Persistent stallion-like behavior is a common sign of cryptorchidism in supposed geldings. The presence of testicular tissue can be evaluated by analyzing hormones such as testosterone and anti-Müllerian hormone (AMH). Here, we used hormonal analysis to investigate relationships between the likely presence of testicular tissue and stallion-like behavior in samples submitted from presumptive geldings (n = 1,202), retrospectively. Most geldings with stallion-like behaviors had serum concentrations of testosterone (851/1,056; 80.6 %) and AMH (682/877; 77.8 %) below the laboratory reference range for cryptorchids (< 60 pg/mL and ≤ 0.15 ng/mL for testosterone and AMH, respectively). A total of 13 samples (13/716; 1.8 %) showed AMH concentrations typical for geldings but testosterone above the cryptorchid range. Conversely, 31 samples (31/716; 4.3 %) had high AMH, suggesting cryptorchidism, but testosterone concentrations implied no testicular tissue. Among the cryptorchid stallions, the AMH and testosterone concentrations did not vary based on the season. However, age categories affected the concentration of both hormones among the presumptive true cryptorchid stallions. The results of this study demonstrate that undesirable behavior in geldings is rarely associated with the presence of testicular tissue, as assessed by these two hormonal biomarkers. This information highlights the complexity of behavior and demonstrates that persistent stallion-like behavior in geldings could be related to factors other than the presence of testicular tissue.

Sperm Quality Assessment in Stallions: How to Choose Relevant Assays to Answer Clinical Questions

Stallion sperm analysis is indicated for infertility diagnosis, pre-sale expertise, production of fresh or frozen doses, and frozen straw quality control. Various collection methods are described, and numerous assays can be performed on semen. Determining an approach for each of these cases is challenging. This review aims to discuss how to obtain relevant clinical results, answering stallion owners' concerns. Semen can be collected with an artificial vagina on a phantom or a mare, by electro-ejaculation under anesthesia, or after pharmacological induction. The collection method influences the semen volume and concentration, while the total sperm number depends on the testicular production and collection frequency. In the seminal plasma, acidity, pro-oxidant activity, and some enzymes have repercussions for the semen quality and its conservation. Moreover, non-sperm cells of seminal plasma may impact semen conservation. Motility analysis remains a core parameter, as it is associated with fresh or frozen dose fertility. Computer-assisted motility analyzers have improved repeatability, but the reproducibility between laboratories depends on the settings that are used. Morphology analysis showing spermatozoa defects is useful to understand production and maturation abnormalities. Staining of the spermatozoa is used to evaluate viability, but recent advances in flow cytometry and in fluorochromes enable an evaluation of multiple intracellular parameters. Spermatozoa protein expression already has clinical applications, for example, as a fertility and freezing ability predictor. At present, stallion semen analysis ranges from macroscopic evaluation to assessing spermatozoa proteins. However, clinically, all these data may not be relevant, and the lack of standardization may complicate their interpretation.

Development of a chronic focal equine arteritis virus infection of a male reproductive tract cell line

Equine arteritis virus (EAV) is an Alphaarterivirus (family Arteriviridae, order Nidovirales) that frequently causes an influenza-like illness in adult horses, but can also cause the abortions in mares and death of newborn foals. Once primary infection has been established, EAV can persist in the reproductive tract of some stallions. However, the mechanisms enabling this persistence, which depends on testosterone, remain largely unknown. We aimed to establish an in vitro model of non-cytopathic EAV infection to study viral persistence. In this work, we infected several cell lines originating from the male reproductive tract of different species. EAV infection was fully cytopathic for 92BR (donkey cells) and DDT1 MF-2 (hamster cells) cells, and less cytopathic for PC-3 cells (human cells); ST cells (porcine cells) seemed to eliminate the virus; LNCaP (human cells) and GC-1 spg (murine cells) cells were not permissive to EAV infection; finally, TM3 cells (murine cells) were permissive to EAV infection without any overt cytopathic effects. Infected TM3 cells can be maintained at least 7 days in culture without any subculture. They can also be subcultured over 39 days (subculturing them at 1:2 the first time at 5 dpi and then every 2-3 days), but in this case, the percentage of infected cells remains low. Infected TM3 cells may therefore provide a new model to study the host-pathogen interactions and to help determine the mechanisms involved in EAV persistence in stallion reproductive tract.

Effects of two different management systems on hormonal, behavioral, and semen quality in male dromedary camels

Effects of two different management systems on male dromedary camel hormones, behaviors, and semen parameters were documented. Camels (n=6) were tested under two management systems: (i) housed in single boxes with 1-h freedom (H23); (ii) exposed to females for 17 h (from 3.30 p.m. to 8.30 a.m.) and then housed (ConExF). Blood was collected every morning; camel behavior was recorded twice a day: (i) from 7:00 to 8:00 a.m. to determine the short effects; (ii) from 2:00 to 3:00 p.m. to determine the long effects. Each camel underwent a female parade and semen collection thrice a week; sexual behavior, libido, and semen parameters were assessed. Testosterone and cortisol concentrations were higher in ConExF than H23. Compared to the H23 group, ConExF group spent more time walking, standing tripods, and looking outside their pen/box but they spent less time eating, ruminating, resting, standing, and showing stereotypical behaviors. In the morning, ConExF group spent more time walking, ruminating, and showing typical sexual behaviors compared to themselves during afternoon time and the H23 group. However, in the afternoon time, ConExF camels put more time their heads outside the box through the window and showed higher frequencies of stereotypies, probably due to a higher level of frustration. While the sexual behavioral score was higher and ejaculates showed a higher fraction of milky white and white-colored semen in ConExF than H23 group, their libido was similar. Overall, 17 h of exposure led to an increase in testosterone and cortisol levels, enhancing sexual behavior and semen color, but leading to frustration.

Case Report: Suppression of Harem Stallion Behavior and Fertility Following Anti-Gonadotropin-Releasing Hormone Vaccination of a Captive Wild Przewalski's Horse (Equus ferus przewalskii)

This report describes an option to modulate the testicular function of wild horses and field methods to assess it. Non-surgical castration of a captive wild Przewalski's stallion with anti-gonadotropin-releasing hormone (GnRH) immunization was performed by sub-cutaneous injection of two doses of 450 μg (3 ml) of GnRH conjugated to diphtheria toxin, further repeated every 6 months. Semen quality was assessed after collection by electro-ejaculation under general anesthesia. Endocrine and behavioral consequences were studied during a 2-year follow-up period. The procedure of electro-ejaculation was safe and effective to collect spermatozoa. Motility was low but was improved by a significant dilution of sample (1v/4v−1v/5v) after collection. Immuno-neutering resulted in a decrease of the total spermatozoa number and motility 1 month after primary vaccination. However, infertility could not yet be guaranteed. Six months post-vaccination, serum testosterone concentrations had decreased and the treated stallion had lost his harem stallion role. Moreover, at the same time, the total spermatozoa number was near zero with no motile spermatozoa, and offspring was no longer observed. As a conclusion, electro-ejaculation under general anesthesia is suitable on wild horses to obtain spermatozoa that should be washed or largely diluted before use for artificial insemination (AI) programs. Anti-GnRH immuno-neutering protocol led to a dramatic decrease of spermatozoa number, motility, and testosterone production. This also induced deep changes in the social structure of the band. Such technique could be considered as an alternative to surgical castration in wild horses.

Half a century of equine reproduction research and application: A veterinary tour de force

Over the past 50 years, per season pregnancy rate in Thoroughbred mares have risen from 70 to >90% and foaling rates from 55 to >80%. Some of the significant pharmacological treatments and diagnostic methods which have driven this marked improvement in breeding efficiency are reviewed. They include the application of artificial lighting to hasten the onset of ovulatory oestrous cyclicity in early Spring, rapid steroid hormone assays to aid in determining the stage and normality of the mare's cycle, prostaglandin analogues, synthetic progestagens and Gonadotrophin-releasing Hormone (GnRH) analogues to better control and manipulate her cycle to good effect, transrectal ultrasound scanning to monitor follicle growth, endometrial architecture and ovulation and to allow accurate, early pregnancy diagnosis thereby enabling successful ablation of one of twin conceptuses. Also, flexible videoendoscopy to monitor physiological and pathological changes in the uterine endometrium and rigid laparoscopy to apply prostaglandin to the oviducts to dislodge and clear suspected blockages of them to restore fertility. The outbreak of Contagious Equine Metritis in Newmarket in the spring of 1977 and the swabbing-related changes to mare and stallion management, plus the improved veterinary hygiene methods, which followed are also recounted. The past half century has witnessed many technical and therapeutic advances that have enhanced tremendously the diagnostic and treatment capabilities of studfarm veterinary surgeons. They, in turn, have improved greatly the efficiency of breeding Thoroughbreds and other types of horses.

Effects of a GnRH administration on testosterone profile, libido and semen parameters of dromedary camel bulls

GnRH treatment has been suggested to increase testosterone levels temporarily and to stimulate libido in stallions, but its use has not fully ascertained in dromedary camels. The aim of this work was to study the effects of administering 100 μg of GnRH on testosterone profile, libido and semen parameters in dromedary camels. The same bulls were used as self-controls and experimental group. Blood samples were collected every 20 min (T0-T12) for 4h, and semen collections were performed over a 2-hour period after T12. GnRH was administered immediately after T0. In GnRH-treated bulls, testosterone levels showed an upward trend, peaking after 140 min, and then slowly decreasing. GnRH administration also led to a decrease in mating time and an increase in spermatozoa concentration. Overall, it seems that administration of 100 μg GnRH might increase testosterone levels temporarily and enhance camel reproduction performance.

Effect of different management systems on rutting behavior and behavioral repertoire of housed Maghrebi male camels (Camelus dromedarius)

Camel management has been changing in recent years from an extensive to a semi-intensive or intensive system, particularly for breeding bulls and dairy dromedary camels. Captivity may affect animal welfare, and low libido is the major complaint for housed breeding bulls. Since welfare status could also affect reproductive performance, the aim of this study was to evaluate different management practices on behavior, particularly on sexual behavior, and to identify some behavioral needs of male dromedary camels reared for semen collection. The effects of the following management systems on their behavior were compared: (i) traditional: housing in a single stall for 24 h (H24), (ii) housing in a single stall for 23 h with 1 h free in the paddock (H23), and (iii) housing in a single stall for 22 h and 30 min with 1 h paddock time and 30 min exposure to a female camel herd (ExF). During the trial, blood cortisol concentrations were assessed and camels were filmed daily for 30 min in the mornings and during a female passage in the evenings. Videos were analyzed in order to fill out a focal sampling ethogram and to score sexual behavior. As a result, there were no differences between the H24 and H23 systems, whereas ExF had a significant positive impact on their sexual behavior score and behavioral repertoire, further reducing cortisol levels. Overall, it seems that male dromedary camel welfare status improves when their behavioral needs for social interaction and movement are satisfied.

Use of a deslorelin implant for influencing sex hormones and male behaviour in a stallion - Case report

This case report describes the use of a subcutaneously applied 4.7-mg deslorelin acetate implant in a three-year-old Arabian crossbred stallion showing unwanted strong male behaviour. Following deslorelin acetate implantation the stallion showed a short transitional increase in male behaviour. A 'gelding-like' behaviour was noted 15 days (D15) after treatment. The horse was surgically castrated at the owners request at D52 after treatment. Serum testosterone, oestradiol-17β and oestrone sulphate values decreased after deslorelin acetate implantation, but serum LH and FSH levels remained unchanged. Histopathological analysis of both testes and sperm analysis revealed a reduced spermatogenesis at D52. The testicular volume decreased after treatment. The use of a subcutaneously applied deslorelin acetate implant might be a promising tool to change the behaviour of aggressive stallions.

Effect of pentoxifylline treatment on testicular perfusion and semen quality in Miniature horse stallions

The objective was to investigate the effects of pentoxifylline (PTX) on testicular perfusion and sperm production in stallions. In a preliminary study, six mature Miniature horse stallions were given 0, 8.5, or 17.0 mg/kg of PTX orally, twice daily, for 3 d. Total Arterial Blood Flow Rate (TABFR) was higher (P < 0.05) in all treated versus control stallions during and after treatment. Two months later (during the fall and winter), the same stallions received either 0 or 17 mg/kg of PTX orally, twice daily for 60 d. Resistance and pulsatility indices (RI and PI, respectively) decreased in PTX-treated stallions between Treatment 1 and Post-treatment periods. Arterial diameter, as well as Total Arterial Blood Flow (TABF), decreased in controls between Baseline and Treatment 1 (P < 0.05). A similar decrease in arterial diameter was delayed in Group TREATED, but reached significance during Post-treatment (P < 0.05), whereas TABF did not change in this group. Furthermore, TABFR had a transient tendency to increase during Treatment 1 (P < 0.1), whereas it steadily decreased in controls and reached significance in the Post-treatment period (P < 0.05). Both RI and PI were negatively correlated with end diastolic velocity (EDV) in both groups (P < 0.0001). There were positive correlations between RI and peak systolic velocity (PSV) in treated stallions during Treatment 1 (RI: r = 0.53, P = 0.021; PI: r = 0.59, P = 0.007). Also, there were negative correlations between Time Averaged Maximum Velocity (TAMAX) and Doppler indexes in treated stallions during Treatment 2 period (RI: r = -0.49, P = 0.006; PI: r = -0.47, P = 0.008), and during Post-treatment periods (RI: r = -0.40, P = 0.049; PI: r = -042, P = 0.039). Transient hydrocele occurred in all treated stallions (a potential complication of high-dose PTX). Semen end points were not significantly affected by PTX treatment. In conclusion, PTX delayed the seasonal decrease of testicular perfusion in stallions. Sperm quality and quantity were not significantly affected; perhaps they would have been enhanced by prolonged treatment.