In vitro comparison of 3 techniques of prosthesis attachment to the muscular process of the equine arytenoid cartilage.

OBJECTIVE: To determine the degree and ease of arytenoid abduction achieved with abaxial placement of a FASTak II suture anchor compared to 2 suture patterns with different directions of insertion-caudomedial to craniolateral and medial to lateral. STUDY DESIGN: Ex vivo experimental. STUDY POPULATION: Cadaveric larynges from 10 Standardbred racehorses. METHODS: Each larynx was sequentially instrumented with all 3 arytenoid suture attachment in random order: (1) abaxial placement of a FASTak II suture, (2) caudomedial to craniolateral suture, and (3) medial to lateral suture placement. Each construct was abducted at 5N increments from 0 to 25N and the left to right quotient angle ratio (LRQ) measured from digital pictures acquired at each sequential increment. RESULTS: Arytenoid abduction (higher LRQ) was greater with FASTak II construct than either of the suture patterns. The largest difference occurred at 5N. Approximately 50% less force was required to achieve an LRQ of 1.0 with the FASTak II anchor compared to the suture patterns. No difference was detected between the 2 suture constructs throughout the study. CONCLUSION: Use of the FASTak II suture anchor improved arytenoid abduction compared to 2 suture patterns and minimized the suture loads required to achieve maximum arytenoid abduction. CLINICAL RELEVANCE: Use of the FASTak II anchor may decrease the suture load required to achieve arytenoid abduction in clinical cases. This may reduce the load placed on the laryngoplasty, thereby, minimizing postoperative loss of abduction.

Standing left recurrent laryngeal neurectomy for prospective evaluation of laryngeal hemiplegia evaluated by a high-speed treadmill test.

OBJECTIVE: To describe left recurrent laryngeal neurectomy (LRLn) performed under standing sedation and evaluate the effect of LRLn on upper respiratory tract function using a high-speed treadmill test (HST). We hypothesized that (1) unilateral LRLn could be performed in standing horses, resulting in ipsilateral arytenoid cartilage collapse (ACC); and (2) HST after LRLn would be associated with alterations in upper respiratory function consistent with dynamic ACC. ANIMALS: 6 Thoroughbred horses. METHODS: The horses were trained and underwent a baseline HST up to 14 m/s at 5% incline until fatigue. Evaluation included; airflow, pharyngeal and tracheal pressures, and dynamic upper respiratory tract endoscopy. Trans-laryngeal impedance (TLI) and left-to-right quotient angle ratio (LRQ) were calculated after testing. The following day, standing LRLn was performed in the mid-cervical region. A HST was repeated within 4 days after surgery. RESULTS: Standing LRLn was performed without complication resulting in Havemayer grade 4 ACC at rest (complete paralysis) and Rakestraw grade C or D ACC (collapse up to or beyond rima glottis midline) during exercise. Increasing treadmill speed from 11 to 14 m/s increased TLI (P < .001) and reduced LRQ (P < .001). Neurectomy resulted in an increase in TLI (P = .021) and a reduction in LRQ (P < .001). CLINICAL RELEVANCE: Standing LRLn induces laryngeal hemiplegia that can be evaluated using a HST closely after neurectomy. Standing LRLn may be useful for future prospective evaluations of surgical interventions for laryngeal hemiplegia.

Yearling laryngeal function in Thoroughbreds that underwent a laryngoplasty differs from controls.

BACKGROUND: Yearling laryngeal function (YLF) is frequently assessed at the time of sale and the outcomes of these assessments can have significant economic implications. The YLF of horses that subsequently underwent a prosthetic laryngoplasty (PL) is unknown. OBJECTIVES: We hypothesised horses with YLF ≥grade II.2 would be at increased risk of requiring PL, compared with YLF

Implementation of a prototype dynamic laryngoplasty system in standing sedated horses provided arytenoid abduction control at seven days postoperatively.

OBJECTIVE: Evaluate a prototype dynamic laryngoplasty system (DLPS) in horses; a feasibility study. ANIMALS: 7 healthy Standardbred adult horses. METHODS: This was an in vivo experimental study. Horses had a standing surgical procedure to induce complete laryngeal hemiplegia, which was subsequently treated using the dynamic laryngoplasty system (DLPS). Activation of the DLPS was achieved using an injection port exiting through the skin (n = 2) or a subcutaneous injection port (n = 5). For each horse, endoscopic examinations of the upper respiratory tract were performed preoperatively, intraoperatively, and 7 days postoperatively. Left-to-right quotient ratios calculated during inactivated and activated states were obtained from still images of the rima glottidis acquired during day 7. In 3 horses, the device was intentionally overinflated to evaluate for device failure, and postmortem examinations were performed on day 7. For the remaining 4 horses, upper respiratory tract endoscopy was repeated at 1 month postoperatively, with no subsequent postmortem exam. RESULTS: No perioperative complications occurred, and the DLPS was effectively delivered in all horses under standing sedation. The left-to-right quotient ratio at day 7 postoperatively could be altered from a resting position of 0.76 (± 0.06) to a maximum of 0.97 (± 0.06; P < .05). The degree of arytenoid abduction could not be significantly altered after 1 month of device implantation, suspected to be due to peri-implant fibrosis. No coughing nor tracheal contamination was observed at all time points or during inflation. CLINICAL RELEVANCE: The ability to alter the degree of abduction at 7 days postoperatively with the DLPS may be beneficial in selective cases.

Evaluation of recurrent laryngeal neuropathy in domestic and feral horse populations in Australia using histologic and immunohistochemical analysis: A pilot study.

BACKGROUND: Little is known about potential differences in the left recurrent laryngeal nerve (Lrln) and left cricoarytenoideus dorsalis (LCAD) muscle between domestic and feral horse populations. If a difference exists, feral horses may provide a useful control population for research related to recurrent laryngeal neuropathy (RLN) and increase our understanding of potential population pressures influencing the incidence RLN. OBJECTIVES: The objective of this study was to compare the Lrln and LCAD of domestic and feral horses using histological and immunohistochemical techniques (IHC). METHODS: Sixteen horses, domestic (n = 8) and feral (n = 8), without clinical or ancillary examinations that were processed at an abattoir had the Lrln and LCAD muscle harvested immediately following death. Carcass weights were recorded. Subjective and morphometric histologic assessment were performed on Lrln sections. The LCAD was assessed for myosin heavy chain (fibre type proportion, diameter and grouping using IHC. RESULTS: Fibre-type grouping consistent with RLN was seen in both groups. Regenerating fibre clusters were more common in domestic compared to feral horses (p = 0.04). No other histologic differences occurred between groups. Muscle fibre typing demonstrated a lower mean percentage of type IIX fibres in the feral group compared to the domestic group (p = 0.03). There was no difference in type I or IIA proportions or mean diameter of any fibre type between the groups. CONCLUSIONS: The domestic population showed evidence of nerve regeneration suggesting RLN in this group, yet this was not supported by the higher proportion of type IIX muscle fibres compared to the feral population. Further evaluation to clarify the significance and wider occurrence of the differences is indicated.

The Neuroimmune Interface and Chronic Pain Through the Lens of Production Animals.

Communication between the central nervous system (CNS) and the immune system has gained much attention for its fundamental role in the development of chronic and pathological pain in humans and rodent models. Following peripheral nerve injury, neuroimmune signaling within the CNS plays an important role in the pathophysiological changes in pain sensitivity that lead to chronic pain. In production animals, routine husbandry procedures such as tail docking and castration, often involve some degree of inflammation and peripheral nerve injury and consequently may lead to chronic pain. Our understanding of chronic pain in animals is limited by the difficulty in measuring this pathological pain state. In light of this, we have reviewed the current understanding of chronic pain in production animals. We discuss our ability to measure pain and the implications this has on animal welfare and production outcomes. Further research into the neuroimmune interface in production animals will improve our fundamental understanding of chronic pain and better inform human clinical pain management and animal husbandry practices and interventions.

Continuous Monitoring of the Thermoregulatory Response in Endurance Horses and Trotter Horses During Field Exercise: Baselining for Future Hot Weather Studies.

Establishing proper policies regarding the recognition and prevention of equine heat stress becomes increasingly important, especially in the face of global warming. To assist this, a detailed view of the variability of equine thermoregulation during field exercise and recovery is essential. 13 endurance horses and 12 trotter horses were equipped with continuous monitoring devices [gastrointestinal (GI) pill, heartrate (HR) monitor, and global positioning system] and monitored under cool weather conditions during four endurance rides over a total of 80 km (40 km loops) and intense trotter track-based exercise over 1,540 m. Recordings included GI temperature (T c ), speed, HR and pre- and post-exercise blood values. A temperature time profile curve of T c was constructed, and a net area under the curve was calculated using the trapezoidal method. Metabolic heat production and oxygen cost of transport were also calculated in endurance horses. Maximum T c was compared using an independent samples t-test. Endurance horses (mean speed 14.1 ± 1.7 km h-1) reached mean maximum T c (39.0 ± 0.4°C; 2 × 40 km in 8 horses) during exercise at 75% of completion of T c exercise and T c returned to baseline within 60 min into recovery. However, the mean T c was still 38.8 ± 0.4°C at a HR of 60 bpm which currently governs "fit to continue" competition decisions. Trotters (40.0 ± 2.9 km h-1) reached a comparable mean max T c (38.8 ± 0.5°C; 12 horses) always during recovery. In 30% of trotters, T c was still >39°C at the end of recovery (40 ± 32 min). The study shows that horses are individuals and thermoregulation monitoring should reflect this, no matter what type of exercise is performed. Caution is advised when using HR cut-off values to monitor thermal welfare in horses since we have demonstrated how T c can peak quite some time after finishing exercise. These findings have implications for training and management of performance horses to safeguard equine welfare and to maximize performance.

Effect of head position on radiographic assessment of laryngeal tie-forward procedure in horses.

OBJECTIVE: To assess the effect of head position on relative position of the larynx and hyoid apparatus in horses with palatal dysfunction, and to define a standard position for radiographic assessment of laryngeal tie-forward. STUDY DESIGN: Prospective clinical study. ANIMALS: Adult horses (n=9) with palatal dysfunction. METHODS: Left lateral radiographs of the larynx were obtained pre and postoperatively for 3 different head positions (flexed=90 degrees ; neutral=100 degrees ; extended=115 degrees ). Distance between thyrohyoid bone and thyroid cartilage was measured. Data were analyzed to investigate differences between head positions, and to compare differences between pre- and postoperative measurements. RESULTS: Head position had a significant effect on relative position of the larynx and hyoid apparatus preoperatively. There was no significant difference in postoperative measurements of the 3 head positions. A significant difference between pre- and postoperative measurements was found with the head in the neutral or extended position whereas there were no significant differences between pre- and postoperative measurements using the flexed position. CONCLUSIONS: Head position affects the relationship between the hyoid apparatus and larynx preoperatively, with greatest distance occurring when the head is extended. In a flexed position, it is not possible to ascertain whether laryngeal position has changed postoperatively. CLINICAL RELEVANCE: A standardized head position is necessary when assessing the laryngeal tie-forward procedure radiographically. An extended head position is most useful for this assessment.

Evaluation of a telemetric gastrointestinal pill for continuous monitoring of gastrointestinal temperature in horses at rest and during exercise.

OBJECTIVE To evaluate use of a telemetric gastrointestinal (GI) pill to continuously monitor GI temperature in horses at rest and during exercise and to compare time profiles of GI temperature and rectal temperature. ANIMALS 8 Standardbred horses. PROCEDURES Accuracy and precision of the GI pill and a rectal probe were determined in vitro by comparing temperature measurements with values obtained by a certified resistance temperature detector (RTD) in water baths at various temperatures (37°, 39°, and 41°C). Subsequently, both GI and rectal temperature were recorded in vivo in 8 horses over 3 consecutive days. The GI temperature was recorded continuously, and rectal temperature was recorded for 3.5 hours daily. Comparisons were made between GI temperature and rectal temperature for horses at rest, during exercise, and after exercise. RESULTS Water bath evaluation revealed good agreement between the rectal probe and RTD. However, the GI pill systematically underestimated temperature by 0.14°C. In vivo, GI temperature data were captured with minimal difficulties. Most data loss occurred during the first 16 hours, after which the mean ± SD data loss was 8.6 ± 3.7%. The GI temperature was consistently and significantly higher than rectal temperature with an overall mean temperature difference across time of 0.27°C (range, 0.22° to 0.32°C). Mean measurement cessation point for the GI pill was 5.1 ± 1.0 days after administration. CONCLUSIONS AND CLINICAL RELEVANCE This study revealed that the telemetric GI pill was a reliable and practical method for real-time monitoring of GI temperature in horses.

A quantitative study of the equine soft palate using histomorphometry.

Dorsal displacement of the soft palate is a common cause of upper airway obstruction in racehorses and is of unknown aetiology. To determine whether the palate may displace for structural reasons, knowledge of the normal soft palate is required. The present study aimed to describe, qualitatively and quantitatively, the structure of the normal equine soft palate using histomorphometry. In soft palates from 12 Thoroughbreds, glandular tissue predominated (ca. 40% of total area), located mainly in the rostral and ventral regions. Rostrally, muscles attached to a tendinous aponeurosis located dorsal to the glandular tissue. Muscle was most abundant in the dorsal mid region and decreased caudally. The oral mucosa consisted of a non-keratinised stratified squamous epithelium whereas the nasopharyngeal mucosa was pseudostratified, columnar and ciliated. Elastin fibres were observed in the nasopharyngeal submucosa, becoming more prevalent caudally. The palates were bilaterally symmetrical although the proportion of tissue types varied considerably between individuals.

Evaluation of cytokine mRNA expression in bronchoalveolar lavage cells from horses with inflammatory airway disease.

Inflammatory airway disease (IAD) is a common disorder of performance horses and is associated with poor performance and accumulation of mucus and inflammatory cells in lower airway secretions. Horses with IAD frequently have increased relative counts of neutrophils in bronchoalveolar lavage fluid (BALF); less commonly relative counts of eosinophils and/or mast cells may be increased. The aetiopathogenesis of IAD is unknown and may involve innate and/or acquired immune responses to various factors including respirable dust constituents, micro-organisms, noxious gases and unconditioned air. The molecular pathways and role of the immune system in the pathogenesis of IAD remain poorly defined and it is unknown whether polarised T cell responses occur in the disease, as have been reported to occur in equine recurrent airway obstruction and asthma in humans. Elucidating cytokine responses that develop in horses with IAD may allow a greater understanding of the possible aetiopathological pathway(s) involved and could contribute to development of novel treatments. We compared the mRNA expression of tumour necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), interleukin (IL)-1ß, IL-2, IL-4, IL-8, IL-13, IL-17 and IL-23 in cell pellets extracted from BALF of horses with IAD (n=21) and horses free of respiratory tract disease (n=17). Horses with IAD had significantly increased levels of TNF-α, IL-1ß and IL-23 mRNA; no significant differences in the other cytokine mRNAs were detected. The results of this study indicate that IAD of horses is associated with increased mRNA expression of pro-inflammatory cytokines in BALF cells, which may reflect stimulation of the innate immune responses to inhaled antigens. There was no evidence of a polarised T-cell cytokine response suggesting hypersensitivity responses may not be involved in the aetiopathogenesis of IAD.

Transverse and dorso-ventral changes in thoracic dimension during equine locomotion.

Changes in shape of the equine thorax during locomotion are not well defined, although it has been shown recently that the transverse hemi-diameter changes its dimension by up to 80mm on the side of the trailing forelimb during gallop, despite minimal change in thoracic circumference. The aim of this project was to analyse transverse and dorso-ventral changes in shape of the thorax simultaneously, and to determine if leading limb, treadmill slope and speed have an effect on these shape changes. Reflective markers were placed on the horse's hemi-thorax and movement of the markers was recorded using a motion capture system while the horse trotted and cantered on a treadmill. Treadmill speed and slope, and the lead the horse cantered on were varied to determine the effects these had on transverse hemi-diameter and dorso-ventral diameter. There was a negative correlation between transverse and dorso-ventral changes in thoracic dimension, the strength of which increased with speed on the trailing limb side. On the leading side, the relationship was either weakly negative or positive. The changes in dimension of the hemi-thorax were significantly greater on the trailing side compared to the leading side. Speed had small effects on thoracic shape changes, but inclined exercise caused an increase in transverse hemi-diameter on the trailing side of the thorax. The changes in thoracic shape are unlikely to contribute substantially to ventilation and rib motion is likely to be due to protraction and retraction of the forelimbs. However, it may reflect asynchronous ventilation of lung lobes and partially explain the prevalence of exercise-induced pulmonary haemorrhage.