Quarter Horse Stallion Research Articles

Effect of nutraceutical supplementation on semen quality in stallions.

The use of reproductive biotechnologies in equine practice has shown that some stallions are subfertile, so ways to improve fertility have been sought. This study aimed to evaluate the effect of nutraceutical supplementation on improving semen quality in Quarter Horse stallions. Semen from six Quarter Horse stallions was assessed for 4 months every 20days using the computer-assisted semen analysis system. They were evaluated for 60days before supplementation; then, the same stallions were re-evaluated for 60days with nutraceutical supplementation (30g/day). Volume showed no significant difference (p>0.05) with nutraceuticals. Sperm concentration (10x6 ) was significantly higher with supplementation (339.4±17.5 sperm/mL) than without supplementation (224.6±19.9). Sperm abnormalities (%) were significantly (p<0.05) lower with supplementation (14.3±0.6) than without supplementation (19.1±0.4). Sperm kinematic parameters, total motility (TM), progressive motility (PM), rectilinear velocity (VSL), the velocity of the trajectory (VAP) and curvilinear velocity (VCL), were significantly better with supplementation (p<0.05). Based on the results, it is concluded that nutraceutical supplementation improved semen parameters in Quarter Horse stallions.

142 Methods to concentrate stallion semen for storage

It has been demonstrated that removal of seminal plasma and resuspension of the sperm pellet in various diluents will improve the post storage motility of spermatozoa from some stallions. This normally involves centrifugation. However, a sperm filtering device marketed by Botupharma (Phoenix, AZ) allows removal of seminal plasma without use of a centrifuge. This study was designed with the objective of comparing spermatozoa recovery rates using this device vs. centrifugation with and without a cushion. Thirteen ejaculates were collected from 3 Quarter Horse stallions. Before treatment aliquots were diluted with Dulbecco's modified PBS at a dilution rate of 1:1. For the 2 centrifugation treatments, 12 mL of the diluted semen was placed in a 15 mL conical bottom tube and centrifuged for at 1000g for 20 min with Red Cushion, (Botupharma), or at 400g for 10 mintues without a cushion. Aliquots for the third treatment were also diluted 1:1 and 20mL of the solution and poured into a SpermFilter (Botupharma) for separation. To determine % of sperm recovered, the concentration of aliquots before and after filtration or centrifugation was measured using a densimeter device (ARS, Chino, CA). Data were analyzed by one-way ANOVA with Tukey's test used for pairwise comparisons. Average % recovery rates were 69.4%, and 60.9% for aliquots centrifuged without and with a cushion as compared with 77.6% for the SpermFilter treatment. In this experiment the % recovery was lower (P < 0.02) for those aliquots which were centrifuged with Red Cushion compared with those separated with the SpermFilter. These results could differ if the same procedures were compared with a different technician. Furthermore, because of the diluent used following separation no attempt was made to compare motility following the separation procedures.

Equine cutaneous habronematidosis

Clinical history: A 4-year-old Quarter Horse stallion was unsuccessfully treated for a circumscribed and ulcerated lesion of unknown duration located lateral to the prepuce. Microscopic description: The superficial and deep preputial dermis contains multifocal to coalescing, well-demarcated eosinophilic granulomas characterized by a central area of abundant eosinophilic necrotic debris mixed with degenerate eosinophils surrounded by numerous epithelioid macrophages and occasional multinucleated giant cells (foreign-body type), rimmed by ill-defined layers of fibrous connective tissue. In the center of the granulomas, there are cross-sections of degenerate nematode larvae. The adjacent dermal collagen is expanded by dense inflammatory infiltrate composed mainly of eosinophils and a few lymphocytes and plasma cells. The dermal microvasculature is prominent, with hypertrophic reactive endothelial lining. There is also vascular proliferation amidst perpendicularly oriented plump fibroblasts embedded in collagen (granulation tissue). In addition, there are numerous shrunken, hypereosinophilic, fragmented or hyalinized collagen bundles, occasionally surrounded by degranulated eosinophils.

Surgical treatment of exuberant granulation tissue of the glans penis and paraphimosis in a stallion

SummaryA 15‐year‐old male Quarter Horse stallion was referred with paraphimosis and suspected exuberant granulation tissue (EGT) of the glans penis. Physical examination revealed a painful, voluminous, pink, irregular, cauliflower‐shaped lesion on the penis. Based on the history, anatomical location and clinical presentation EGT was suspected. Histopathology confirmed the diagnosis with no evidence of neoplasia. To obtain breeding soundness, surgical excision of the EGT and reconstruction of the glans penis was recommended. Following surgical removal of the granulation tissue, the stallion recovered without complications and returned to breeding with satisfactory performance including normal libido and mating behaviour.

Two Variants of KIT Causing White Patterning in Stock-Type Horses.

Over 30 polymorphisms in the KIT Proto-Oncogene Receptor Tyrosine Kinase (KIT) gene have been implicated in white spotting patterns ranging from small areas to full dermal depigmentation in the horse. We performed a candidate-gene exon sequencing approach on KIT and MITF, 2 known causatives of white spotting patterns, within 2 families of horses of unknown white spotting. Family 1 (Fam1, N = 5) consisted of a Quarter Horse stallion and 4 offspring with white spotting pattern ranging from legs, lower ventral, and head regions with jagged borders, to almost complete white. The second family (Fam2, N = 7) consisted of 6 half-sibling American Paint Horse/Quarter Horse and their dam, demonstrating unpigmented limbs with belly spots and an extensive white patterning on the face. This approach resulted in 2 variants significantly associated with familial phenotypes, where Fam1 variant is an indel leading to a frameshift mutation, and Fam2 a non-synonymous SNP. We validated the variants within an unrelated population of horses (Fam2 variant, P = 0.00271944) as well as for protein functional impact with ExPASy, Protter, Phyre2, SMART, PROVEAN, SIFT, and I-TASSER, confirming the reported associations. Fam1 associated variant, deemed W31, alters the protein sequence, leading to an early stop codon truncating the normal amino acid sequence from 972 to just 115 amino acids. Fam2 associated variant, deemed W32, may have a subtle impact on receptor function or could be in linkage with a non-coding or regulatory change creating the mild spotting pattern observed in this family.

Successful pregnancies in a mare after laparoscopic unilateral ovariohysterectomy

A 6 year old Thoroughbred mare was presented for investigation of infertility. Over 3consecutive seasons, she had been bred naturally (14 controlled estrous cycles) with 3 Thoroughbredstallions and did not become pregnant. The mare was bred artificially over 3 estrous cycles withsemen from a Quarter horse stallion (known for excellent fertility). Both ovaries appeared functional.During embryo collection on day 7 postovulation, failure of appropriate dilation of left uterine hornwas noticed after embryo collecting medium was infused. Diagnostic hysteroscopy was performedand partial patency defect of the left uterine horn was identified. After sedation and local anesthesia, aunilateral laparoscopic ovariohysterectomy was performed while the mare was standing.Approximately 80% of the left uterine horn was removed using a vasculature sealing device toprovide hemostasis and intracorporeal suturing technique was used for uterine closure. Subsequently,the mare became pregnant and foaled twice.

Chromobacterium violaceum Infection in a Horse

Chromobacterium violaceum is an opportunistic pathogen of mammals that produces characteristic violet pigment in bacterial culture. We report pneumonia and septicaemia caused by C. violaceum in a horse. Necropsy examination was performed on a 3-year-old Quarter Horse stallion with a history of recurrent episodes of pneumonia, fever, dyspnoea and sanguineous nasal discharge. The lungs were not collapsed, but they contained dark red foci mixed with white areas, and multiple nodules of firm consistency. Within the liver and kidney there were randomly distributed, multifocal, white pinpoint lesions (0.1-0.5cm diameter) in the capsule and extending into the parenchyma. The brain and spinal cord contained numerous petechiae. Microscopically, the lung had severe multifocal to coalescing infiltration of degenerate neutrophils within the alveoli and parenchyma associated with extensive areas of necrosis and haemorrhage. Rod-shaped bacteria were often present in the centre of the lesions. There was intense intra-alveolar exudation of fibrin and fibrinoid degeneration of blood vessels associated with thrombosis and ischaemic necrosis adjacent to areas of severe haemorrhage. Similar lesions were present in the liver and kidneys. A pure culture of C. violaceum was obtained from samples of the lung and liver. The identity of the organism was confirmed by amplifying and sequencing the 16S rRNA gene with subsequent analysis of sequence similarity.

The relationship between mitochondrial DNA copy number and stallion sperm function

Mitochondrial DNA (mtDNA) copy number has been utilized as a measure of sperm quality in several species including mice, dogs, and humans, and has been suggested as a potential biomarker of fertility in stallion sperm. The results of the present study extend this recent discovery using sperm samples from American Quarter Horse stallions of varying age. By determining copy number of three mitochondrial genes, cytochrome b (CYTB), NADH dehydrogenase 1 (ND1) and NADH dehydrogenase 4 (ND4), instead of a single gene, we demonstrate an improved understanding of mtDNA fate in stallion sperm mitochondria following spermatogenesis. Sperm samples from 37 stallions ranging from 3 to 24 years old were collected at four breeding ranches in north and central Texas during the 2015 breeding season. Samples were analyzed for sperm motion characteristics, nuclear DNA denaturability and mtDNA copy number. Mitochondrial DNA content in individual sperm was determined by real-time qPCR and normalized with a single copy nuclear gene, Beta actin. Exploratory correlation analysis revealed that total motility was negatively correlated with CYTB copy number and sperm chromatin structure. Stallion age did not have a significant effect on copy number for any of the genes. Copy number differences existed between the three genes with CYTB having the greatest number of copies (20.6 ± 1.2 copies, range: 6.0 to 41.1) followed by ND4 (15.5 ± 0.8 copies, range: 6.7 to 27.8) and finally ND1 (12.0 ± 1.0 copies, range: 0.4 to 26.6) (P < 0.05). Varying copy number across mitochondrial genes is likely to be a result of mtDNA fragmentation and degradation since downregulation of sperm mtDNA occurs during spermatogenesis and may be important for normal sperm function. Beta regression analysis suggested that for every unit increase in mtDNA copy number of CYTB, there was a 4% decrease in the odds of sperm movement (P = 0.001). Influential analysis suggested that results are robust and not highly influenced by data from individual stallions despite the low number of stallions sampled with low sperm motility. Further genome sequencing is necessary to investigate if mutations or deletions are the underlying causes of inconsistent copy numbers across mitochondrial genes. In conclusion, we show, for the first time, that increased mtDNA copy number is associated with decreased total sperm motility in stallions. We therefore suggest that mtDNA copy number may be an indicator of defective spermatogenesis in stallions.

Identification ofCorynebacterium pseudotuberculosisisolated from muscular abscesses in two horses: First report in Mexico

Summary Two Quarter Horse stallions from the same region in Mexico presented with pectoral abscesses and lameness. Exudate samples were taken from drained muscular abscesses and Corynebacterium pseudotuberculosis, identified by bacteriological techniques and multiplex polymerase chain reaction, was obtained in a pure isolation culture from both samples. The sequences of a hypervariable region of the rpoB gene showed 100% and 99% identity to C. pseudotuberculosis 316 biovar equi (CP003077.1) isolated from a horse. Both strains' sequences were located in the same phylogenetic cluster as other biovar equi strain sequences obtained from GenBank. Both horses responded satisfactorily to treatment, which included surgical procedures and wound management. These study cases proved the infection of Mexican horses with C. pseudotuberculosis; however, the prevalence of this pathogen remains unknown.

Ultrastructural mitochondrial alterations in Equine myopathies of unknown origin

Background: Very few mitochondrial myopathies have been described in horses.Objective: To examine the ultrastructure of muscle mitochondria in equine cases of myopathy of unknown origin.Materials & methods: Biopsies of vastus lateralis of the Musculus quadriceps femoris were taken predominantly immediately post mortem and processed for transmission electron microscopy. As a result, electron micrographs of 90 horses in total were available for analysis comprising 4 control horses, 16 horses suffering from myopathy and 70 otherwise diseased horses.Results: Following a thorough clinical and laboratory work-up, four out of five patients that did not fit into the usual algorithm to detect known causes of myopathy showed ultrastructural mitochondrial alterations. Small mitochondria with zones with complete disruption of cristae associated with lactic acidemia were detected in a 17-year-old pony mare, extremely long and slender mitochondria with longitudinal cristae in a 5-year-old Quarter horse stallion, a mixture of irregular extremely large mitochondria (measuring 2500 by 800 nm) next to smaller ones in an 8-year-old Hanoverian mare and round mitochondria with only few cristae in a 11-year-old pony gelding. It remains uncertain whether the subsarcolemmal mitochondrial accumulations observed in the fifth patient have any pathological significance.Conclusions: Ultrastructural alterations in mitochondria were detected in at least four horses. To conclude that these are due to mitochondrial dysfuntions, biochemical tests should be performed.Practical applications: The possibility of a mitochondrial myopathy should be included in the differential diagnosis of muscle weakness.

Eficiência dos diluidores Tris e Botu-crio® sobre os parâmetros seminais de garanhões das raças quarto de milha e mangalarga marchador

O principal fator a limitar o processo de criopreservação de sêmen equino está relacionado à própria espécie, por apresentar uma grande variabilidade nas características dos ejaculados pós-descongelação. O objetivo desta pesquisa foi avaliar a viabilidade espermática pós-descongelação, do sêmen de garanhões das raças Quarto de Milha e Mangalarga Marchador utilizando-se dois diluentes (Tris e Botu-crio®) na criopreservação. Para tanto, foram analisadas as características físicas do sêmen fresco, funcionalidade da membrana espermática pelo Teste Hiposmótico (HOST), motilidade total e vigor pelo Teste de Termoresistência (TTR), motilidade progressiva pelo sistema computadorizado CASA (Computer Assisted Sêmen Anlyses) e integridade da membrana espermática, do acrossoma e funcionalidade de mitocôndria por microscopia de epifluorescência. O diluente Botu-crio® preservou melhor os valores de motilidade e vigor e a integridade de membrana plasmática, pós-descongelamento. Não houve diferença significativa entre as raças quanto à motilidade total e vigor no sêmen fresco, bem como para a análise desses parâmetros no Teste de Termoresistência pós-descongelamento. Garanhões da raça Quarto de Milha apresentaram percentual maior de defeitos maiores na análise de patologia espermática.

Dexamethasone treatment of stallions impairs testosterone biosynthesis at a late step: Glutathione S-transferase A3 isomerization of Δ5-androstenedione

Dexamethasone, a synthetic glucocorticoid, is used as an anti-inflammatory agent in horses. Similar to endogenous stress hormones, dexamethasone lowers serum testosterone within 4 h with levels recovering as early as 24 h post-injection. Weeks later, numbers of motile sperm with normal morphology decrease greatly. To explore the mechanism by which dexamethasone down-regulates testosterone biosynthesis, four adult Quarter Horse stallions were injected i.v. with 0.1 mg/kg dexamethasone while four others received saline. Within 10 h of dexamethasone injection, serum testosterone and cortisol were decreased by 60% and 87%, respectively. Twelve h after injection, stallions were castrated and testes recovered. Testis RNA samples were analyzed on Codelink microarrays carrying 55,000 probes for human mRNAs, as described in Davidson et al. (Cancer Res 64: 6797-6804, 2004). A novel gene, glutathione S-transferase A3 (GSTA3), was discovered to be down-regulated by dexamethasone. GSTA3 is a member of a closely related family of enzymes. While GSTA1, GSTA2 and GSTA4 genes arewidely expressed across tissues, GSTA3 gene expression is restricted to steroidogenic tissues in species using the D5-pathway of steroidogenesis, which include livestock species and humans but not rodents. Quantitative PCR, using primers that distinguish GSTA3mRNA from the other GSTAmRNAs, detected a 49% decrease in GSTA3 mRNA concentrations in testes of dexamethasone-treated stallions. The same primers were

The relationships between scrotal surface temperature, age and sperm quality in stallions

In horses, spermatogenesis normally occurs at an average intratesticular temperature of 35°C; therefore, mechanisms for testicular thermoregulation are essential. Measuring the scrotal surface temperature by thermography is one of the methodologies used to evaluate the effectiveness of testicular thermoregulation. The objective of this study was to determine the relationship between the control of scrotal surface temperature and sperm quality in horses of different ages. In total, 24 Quarter Horse stallions were divided into three groups: YS (young stallions), AS (adult stallions) and OS (old stallions). Initially, we calculated the testicular volume (TV) and evaluated various aspects of the semen (sperm kinetics, plasma membrane integrity and sperm morphology) for all the animals. We also evaluated rectal temperature (RT), body surface temperature (BST,) and average scrotal surface temperature in the testicular region (SST) before (M0) and after sun exposure (M1). Differences were observed (p<0.05) between the RT and BST before and after sun exposure in all three groups. However, there were no differences (p>0.05) in the SST values at these two time points, thus demonstrating the efficiency of the mechanisms for testicular thermoregulation. The SST was similar (p>0.05) among all three groups. Based on these results, we conclude that fertile stallions of different age groups are able to maintain SST and measuring the heat radiating from the scrotum using a digital infrared thermographer. We can also conclude that measuring the heat radiating from the scrotum using a digital infrared thermographer is a practical and efficient tool for monitoring SST in horses.

Management and Outcome of a Non-iatrogenic, Nearly Circumferential, Full-thickness Retroperitoneal Rectal Tear in a Horse

An 8-year-old Quarter Horse stallion presented to the Veterinary Teaching Hospital for evaluation of acute colic and a suspected rectal tear. Clinical examination revealed a nearly circumferential retroperitoneal full-thickness rectal tear. Exploratory laparotomy was performed, and medical management of the tear continued for 6 weeks. Multiple attempts at direct suturing of the tear were unsuccessful. Despite intensive medical management, the horse was not able to defecate, and the tear did not heal adequately, so the horse was humanely euthanized. Necropsy revealed complete obliteration of the muscular layers of the rectum with only a small area of rectal mucosa intact dorsally. There is limited information available on the management of circumferential rectal tears. Based upon this experience and other historical reports, a poor prognosis may be expected for circumferential full-thickness retroperitoneal rectal tears involving the ventral aspect of the rectum.

Ultrastructural Mitochondrial Alterations in Equine Myopathies of Unknown Origin

Background: Very few mitochondrial myopathies have been described in horses.Objective: To examine the ultrastructure of muscle mitochondria in equine cases of myopathy of unknown origin.Materials & methods: Biopsies of vastus lateralis of the Musculus quadriceps femoris were taken predominantly immediately post mortem and processed for transmission electron microscopy. As a result, electron micrographs of 90 horses in total were available for analysis comprising 4 control horses, 16 horses suffering from myopathy and 70 otherwise diseased horses.Results: Following a thorough clinical and laboratory work-up, four out of five patients that did not fit into the usual algorithm to detect known causes of myopathy showed ultrastructural mitochondrial alterations. Small mitochondria with zones with complete disruption of cristae associated with lactic acidemia were detected in a 17-year-old pony mare, extremely long and slender mitochondria with longitudinal cristae in a 5-year-old Quarter horse stallion, a mixt...

157 EFFECT OF DENSITY GRADIENT SELECTION ON EMBRYO RECOVERY RATES OF FRESH AND COOLED STALLION SEMEN

The aim of this study was to improve the spermatic kinetic parameters from stallions with poor quality of fresh and chilled semen by the use of density gradient Equipure™ (Nidacon, Mölndal, Sweden). Semen from 5 Quarter Horse stallions aged 8 and 16 years with history of low embryo recovery rates were used. The kinetics sperm evaluation was performed by computerized semen analysis (CASA) and plasma membrane integrity with fluorescent probes. The average motility parameters for fresh semen before selection were total motility (MT) 60%, progressive motility (PM) 30%, and plasma membrane integrity (IMP) 60% and for cooled semen (24 h at 5°C) were: MT 50%, MP 18%, and 50% IMP. For the group of fresh and cooled semen with no density gradient selection (NS), mares were inseminated with 1 billion viable sperm diluted in skim milk extender in the uterine body, 24 h after ovulation induction with 1 mg of deslorelin. For EquipureTM selection group (SE) semen was concentrated through Spermfilter membrane™ and resuspended in 5 mL of BotuSemenTM (BotupharmaTM, Brazil). In a 15 mL conic tube 5 mL of EquipureTM was added and another part containing 5 mL of the resuspended sperm was slowly added over the EquipureTM column. The 15 mL conic tube was centrifuged at 400g for 20 min. After centrifugation, the sperm pellet was carefully aspirated and to the pellet was resuspended in 4 mL of BotucrioTM. The sperm recovery rate with EquipureTM was 40%. Deep uterine AI was performed 24 h after ovulation induction with 1 mg of deslorelin. Data were analyzed by ANOVA followed by Tukey’s test (P &lt; 0.05). The analysis of semen after EquipureTM selection resulted in average: 75, 35, 65, and 40%, respectively, for MT, MP, and IMP index and sperm recovery. The embryo recovery rate from the 5 stallions showed the following results: Stallion 1 (fresh semen): 12 mares (NS)/4 embryos (33%) and for group SE 22 mares/16 embryos, (72%; P ≤ 0.05). Stallion 2 (fresh semen): 9 mares (NS)/4 embryos, (44%) and for group SE, 12 mares/8 embryos (66%; P &gt; 0.1). Stallion 3 (fresh semen): 4 mares (NS)/1 embryo (25%) and 7 mares for SE/4 embryos (57%; P &gt; 0.1). Stallion 4 (chilled semen): 4 mares (NS)/0 embryo 0% and for SE group 8 mares/6 embryos 75%; P ≤ 0.001). Stallion 5 (chilled semen): 10 mares (NS)/2 embryos (20%) and for SE 6 mares/3 embryos (50%; P &gt; 0.1). For the overall results, 39 inseminations were performed on the no selected group and 11 embryos recovered (28%) for the selected group 55 inseminations and 37 embryos recovered (67%; P &lt; 0.01). The results clearly showed that selection by sperm density gradient EquipureTM was a very effective technique that allowed an improvement on semen quality and fertility. The authors acknowledge support from FAPESP and Botupharma.

The addition of ticarcillin‐clavulanic acid to INRA 96 extender for stallion semen cooling

A commonly used commercial extender (i.e. INRA 96) contains antimicrobials that may have limited effectiveness. Therefore, addition of ticarcillin-clavulanic acid to this extender is a widespread procedure in the equine breeding industry in the United States. However, such practice has not been critically evaluated. To evaluate the addition of ticarcillin-clavulanic acid to INRA 96 and different extender and antimicrobial storage conditions on sperm function and antimicrobial effectiveness. Gel-free semen (42 ejaculates from 14 mature Quarter Horse stallions) was extended with INRA 96 and stored for 24 h in an Equitainer II. The effects of added ticarcillin-clavulanic acid and different extender storage procedures on sperm motion characteristics (by computer-assisted analysis), sperm membrane integrity (by fluorescence-based measurement) and suppression of bacterial growth (by aerobic and anaerobic culture methods) were evaluated using analysis-of-variance and Chi-square statistical methods. The P value for significance was set at < 0.05. Freezing and thawing of modified or unmodified extender prior to use for stallion semen resulted in reduced sperm quality post cooling for 24 h, as evidenced by a significant reduction in sperm motility (i.e. total and progressive) and sperm membrane integrity. Addition of ticarcillin-clavulanic acid to extender resulted in higher sperm velocity when the reconstituted antimicrobial was subjected to cooled storage, as compared with frozen storage, prior to use. Only 28 of 42 ejaculates (67%) yielded presence of bacteria in neat semen but addition of ticarcillin-clavulanic acid to INRA 96 was not different than INRA 96 alone for inhibiting growth of bacteria (98 vs. 94%, respectively). Addition of ticarcillin-clavulanic acid (1 mg/ml) to INRA 96 did not adversely affect sperm quality in extended semen after cooled storage. Extender freezing and thawing prior to use had detrimental effects on sperm quality. These data suggest that INRA 96 should not be frozen and thawed prior to use. Addition of ticarcillin-clavulanic acid to INRA 96 did not impair sperm quality. All extender treatments effectively controlled the bacterial growth compared with neat semen.

Comparison of sperm DNA fragmentation and motility parameters between Quarter Horse and Mangalarga Marchador stallions

Comparison of sperm DNA fragmentation and motility parameters between Quarter Horse and Mangalarga Marchador stallions

Case Study of Processing and Insemination Techniques: Attempts to Improve Fertility of an Aged Stallion with Dilute Semen of Poor Quality

The objective of this case study was to investigate whether semen centrifugation and low-dose insemination techniques would improve fertility of an aged subfertile Quarter Horse stallion with low sperm concentration, motility, and morphology in ejaculates. Forty-five mares were bred by one of five treatments (n = 9 per group) using the entire ejaculate as follows: (1) Group Body: body insemination with ejaculate diluted 1:1 in TAMU extender; (2) Group Body-Cent: body insemination after centrifugation and re-suspension of sperm pellet to 1 mL in TAMU extender; (3) Group Horn-Cent: deep horn insemination after centrifugation and re-suspension of sperm pellet to 1 mL in TAMU extender; (4) Group Cent-Hys: hysteroscopic insemination onto the uterotubal papilla after centrifugation and re-suspension of sperm pellet to 200 μL in Kenney-Modified Tyrode’s extender; and (5) Group Dens-Hys: hysteroscopic insemination onto the uterotubal papilla after discontinuous density gradient centrifugation and re-suspension of the sperm pellet in 200-μL Kenney-Modified Tyrode’s extender. Pregnancy rates did not differ among treatment groups ( P = .77). Semen centrifugation for low dose insemination did not appear to improve fertility of this subfertile stallion, despite use of entire ejaculates for each individual insemination dose.

HORSE SPECIES SYMPOSIUM: Contagious equine metritis: An insidious threat to the horse breeding industry in the United States1

Contagious equine metritis (CEM) has given rise to international concern since it was first recognized as a novel venereal disease of equids in 1977 and the etiologic agent was identified as a previously undescribed bacterium, Taylorella equigenitalis. Horse industry concerns over CEM centered on the ease with which this bacterium could be disseminated, the significance of T. equigenitalis as a cause of short-term infertility in the mare, and the existence of the carrier state in the stallion and the mare. The first known outbreak of CEM in the United States was in Kentucky in 1978. The economic impact on the Thoroughbred industry in the state was substantial. Before 2008, additional small-scale outbreaks occurred in Missouri in 1979, Kentucky in 1982, and Wisconsin in 2006, nearly all attributed to the importation of carrier animals. On each occasion, appropriate measures were taken to eliminate the infection, resulting in the United States regaining its CEM-free status. With the exception of the 1978 occurrence in Kentucky, none of the subsequent outbreaks significantly affected the horse industry. That changed dramatically in 2008, however, after the discovery of a Quarter horse stallion in Kentucky that cultured positive. Subsequent investigations turned up 23 carrier stallions and 5 carrier mares belonging to 11 breeds and located in 8 states. Shipment of infective semen and indirect venereal contact in stallion collection centers through the use of contaminated fomites were major factors in the spread of T. equigenitalis. Trace-back investigations of some 1,005 exposed and carrier stallions and mares in 48 states have failed to identify the origin of this latest CEM event. Neither clinical evidence of CEM nor decreased pregnancy rates were reportedly a feature in infected or exposed mares. In light of these findings, there was some question of whether or not the considerable expense incurred in investigating the latest CEM occurrence was warranted. Regaining CEM-free status for the United States will present considerable challenges.