Evaluation and Management of the Recumbent Adult Horse

Hindlimb kinematics, kinetics and muscle dynamics during sit-to-stand and sit-to-walk transitions in emus (Dromaius novaehollandiae)

Terrestrial animals not only need to walk and run but also lie prone to rest and then stand up. Sit-to-stand (STS) and sit-to-walk (STW) transitions are vital behaviours little studied in species other than humans so far, but likely impose biomechanical constraints on limb design because they involve near-maximal excursions of limb joints that should require large length changes and force production from muscles. By integrating data from experiments into musculoskeletal simulations, we analysed joint motions, ground reaction forces, and muscle dynamics during STS and STW in a large terrestrial, bipedal and cursorial bird: the emu (Dromaius novaehollandiae; body mass ∼30 kg). Simulation results suggest that in both STS and STW, emus operate near the functional limits (∼50% of shortening/lengthening) of some of their hindlimb muscles, particularly in distal muscles with limited capacity for length change and leverage. Both movements involved high muscle activations (>50%) and force generation of the major joint extensor muscles early in the transition. STW required larger net joint moments and non-sagittal motions than STS, entailing greater demands for muscle capacity. Whilst our study involves multiple assumptions, our findings lay the groundwork for future studies to understand, for example, how tendon contributions may reduce excessive muscle demands, especially in the distal hindlimb. As the first investigation into how an avian species stands up, this study provides a foundational framework for future comparative studies investigating organismal morphofunctional specialisations and evolution, offering potential robotics and animal welfare applications.

Recumbency decreases mare and foal survival following in-hospital dystocia management

BACKGROUND

Mare and foal survival are increased with prompt dystocia management. Data regarding mortality outcomes in mares and foals, when mares are recumbent at admission for dystocia resolution, are scarce.

OBJECTIVES

To evaluate recumbency at hospital admission as a risk factor for survival of mares and foals following dystocia management. Subsequent mare fertility was also evaluated.

STUDY DESIGN

Retrospective cohort.

METHODS

Data were obtained from medical records at Rood and Riddle Equine Hospital of mares with dystocia between 1995 and 2018. Mare signalment, ambulation status, survival data and foaling records were collected. The proportion of mare survival and mare fertility were analysed using chi-squared tests. Foal survival was analysed using Fisher's exact test. Odds ratios were calculated using multivariable logistic regression.

RESULTS

There were 1038 ambulatory mares and 41 recumbent mares included in the analysis. Survival rates after dystocia resolution were 90.5% (977/1079) in mares and 37.3% (402/1079) in foals. Ambulatory mares had higher odds of survival (OR 6.93, 95% CI: 3.25-14.78, p < 0.001) than recumbent mares. Foals delivered from ambulatory mares had higher odds of survival (OR 22.7, 95% CI: 3.11-165.44, p = 0.002) compared with foals delivered from recumbent mares. Fertility was not statistically different for surviving Thoroughbred mares within 3 years following dystocia resolution between ambulatory and recumbent mares.

MAIN LIMITATIONS

Retrospective study design and small case number of recumbent mares.

CONCLUSIONS

Mare and foal survival was significantly decreased when mares with dystocia were recumbent at hospital admission. Subsequent fertility, as defined for this study, of surviving mares was not affected by ambulation status at the time of dystocia resolution.

Neurological Examination of Horses

The neurological examination is undertaken to determine whether any deficit is due to a lesion in the nervous system and, if so, where within the nervous system any possible lesion or lesions are located. The examination of horses has challenges not encountered when doing the equivalent examination in dogs and cats, principally that spinal reflexes and postural reactions are impossible/difficult to assess in most animals. The anatomy book can be consulted later but at the end of the neurological examination the clinician then should be able to determine broadly which area of the neuromuscular systems is affected.

Evaluation of intramuscular anesthetic protocols in healthy domestic horses

OBJECTIVE

To assess anesthetic induction, recovery quality and cardiopulmonary variables after intramuscular (IM) injection of three drug combinations for immobilization of horses.

STUDY DESIGN

Randomized, blinded, three-way crossover prospective design.

ANIMALS

A total of eight healthy adult horses weighing 470-575 kg.

METHODS

Horses were administered three treatments IM separated by ≥1 week. Combinations were tiletamine-zolazepam (1.2 mg kg^-1), ketamine (1 mg kg^-1) and detomidine (0.04 mg kg^-1) (treatment TKD); ketamine (3 mg kg^-1) and detomidine (0.04 mg kg^-1) (treatment KD); and tiletamine-zolazepam (2.4 mg kg^-1) and detomidine (0.04 mg kg^-1) (treatment TD). Parametric data were analyzed using mixed model linear regression. Nonparametric data were compared using Skillings-Mack test. A p value <0.05 was considered statistically significant.

RESULTS

All horses in treatment TD became recumbent. In treatments KD and TKD, one horse remained standing. PaO₂ 15 minutes after recumbency was significantly lower in treatments TD (p < 0.0005) and TKD (p = 0.001) than in treatment KD. Times to first movement (25 ± 15 minutes) and sternal recumbency (55 ± 11 minutes) in treatment KD were faster than in treatments TD (57 ± 17 and 76 ± 19 minutes; p < 0.0005, p = 0.001) and TKD (45 ± 18 and 73 ± 31 minutes; p = 0.005, p = 0.021). There were no differences in induction quality, muscle relaxation score, number of attempts to stand or recovery quality.

CONCLUSIONS AND CLINICAL RELEVANCE

In domestic horses, IM injections of tiletamine-zolazepam-detomidine resulted in more reliable recumbency with a longer duration when compared with ketamine-detomidine and tiletamine-zolazepam-ketamine-detomidine. Recoveries were comparable among protocols.

Postpartum Polyneuropathy in a Mare: A Case Report

Obstetric paralysis is a generic term used to describe postpartum locomotor alterations resulting from nerve damage, widely reported in cattle, but rare in equines. The aim of this study is to report a case of a peripheral polyneuropathy in a primiparous mare, 3 years old, of Mangalarga Marchador breed, after a dystocia lasting approximately 12 hours. At the time of delivery, the head of the fetus was exposed in the vulva and there was flexion of the thoracic limbs. These events culminated in a framework of extreme abduction of the pelvic limbs, thus generating functional impotence and leading the animal to adopt a frog anddecubitus position. After three days of treatment with no improvement in the clinical framework, the animal was euthanized. In the postmortem examination, perineural hemorrhagic lesions were observed in the obturator and sciatic nerves, characterizing the diagnosis of obstetric paralysis. It is possible the outcome of the case would have been satisfactory if there had been an early fetotomy or postpartum treatment had been more prolonged; however, these measures depend on the availability of equipment, conditions of care, and consideration of the owner.

Initial testing of a computer-integrated weight compensation system for rehabilitation of horses

Management of severely injured or neurologic horses is challenging, with ambulatory support limited to static lifts and rescue slings. The aim of this study was initial testing and adjustment of a novel computer-integrated dynamic lift system, including measuring effects of increasing weight compensation (i.e. load reduction) and time attached to the lift. This automated system was developed to improve outcomes and reduce complications in horses with ambulatory difficulties, allowing for controlled mobility and varying load carried by the horse with independent front and hind limb support. Two healthy Thoroughbred horses were studied using the Anderson rescue sling. The lift was programmed to respond to weight and movement of horses. Weight compensation (% bodyweight) was incrementally increased, for front and hind limbs, to maximum percent tolerated, based on heart/respiratory rates and behavioural scoring. The time attached to the lift was then incrementally increased at maximum tolerated weight compensation previously determined. Measures included heart/respiratory rates, behavioural scoring, muscle enzyme activity and blood flow to distal limbs. Results were analysed descriptively. Avoidance behaviour was observed at front and hind end weight compensation of 18 and 4%, respectively. Average maximum time attached to the lift was 2.25 hours. After 60 minutes, respiratory rate increased >20 breaths (b)/minute, reaching 60 b/minute in one horse and 36 b/minute in the other, with shallow breathing. Other measures remained normal. In conclusion, lift programming was successful for weight compensation and mobility during lift support. Complications included avoidance behaviour and respiratory distress at >20% weight compensation, likely caused by the Anderson rescue sling. To address these limitations, a new rehabilitation harness better suited for long-term use is under development.

Limb Kinematics, Kinetics and Muscle Dynamics During the Sit-to-Stand Transition in Greyhounds

Standing up from a prone position is a critical daily activity for animals: failing to do so effectively may cause an injurious fall or increase predation susceptibility. This sit-to-stand behaviour (StS) is biomechanically interesting because it necessitates transitioning through near-maximal joint motion ranges from a crouched (i.e., poor mechanical advantage) to a more upright posture. Such large joint excursions should require large length changes of muscle-tendon units. Here we integrate experimental and musculoskeletal simulation methods to quantify the joint motions, limb forces, and muscle fibre forces, activations and length changes during StS in an extreme athlete-the greyhound-which has large hindlimb muscles bearing short-fibred distal muscles and long tendons. Study results indicate that hindlimb anti-gravity muscle fibres operate near their ~50% limits of length change during StS; mostly by starting at highly lengthened positions. StS also requires high muscle activations (>50%), in part due to non-sagittal motions. Finally, StS movements require passive non-muscular support in the distal hindlimb where short-fibred muscles are incapable of sustaining StS themselves. Non-locomotor behaviours like StS likely impose important trade-offs between muscle fibre force capacity and length changes, as well as active and passive mechanisms of support, that have been neglected in locomotor biomechanics studies.

Mechanical ventilation and management of an adult horse with presumptive botulism

OBJECTIVE

To describe the clinical course, management, and outcome of a horse with a presumptive diagnosis of botulism treated with long-term mechanical ventilation.

CASE SUMMARY

A 6-year-old Quarter Horse gelding with a history of esophageal obstruction was evaluated for progressive tetraparesis. Generalized and progressive skeletal muscle weakness characterized by recumbency, decreased tongue, tail, eyelid, and anal tone, and respiratory failure was observed. Anticholinergic signs including decreased salivation, xerophthalmia, and ileus were also noted. A presumptive diagnosis of botulism was made, although mouse inoculation and spore identification testing were negative. Pentavalent botulism antitoxin was administered on Day 3. The horse was maintained on a water mattress and was managed with mechanical ventilation for 2 weeks. Complications encountered included necrotic rhinitis, intertrigo, decubital ulceration, jugular and cephalic vein thrombophlebitis, corneal ulceration, and transient ventricular tachycardia. The horse showed marked improvement in skeletal muscle strength and parasympathetic nervous system function, allowing it to be successfully weaned from the ventilator but suffered large colon volvulus on Day 21 and was euthanized.

NEW OR UNIQUE INFORMATION PROVIDED

To the authors' knowledge, this is the first report of successful weaning from long-term mechanical ventilation and management of recumbency using a water mattress in an adult horse with presumptive botulism.

Factors associated with survival in 148 recumbent horses

REASONS FOR PERFORMING STUDY

There are currently few data available on the prognosis and outcome of recumbent horses.

OBJECTIVES

To investigate the outcome of hospitalised horses that had been recumbent in the field or hospital and factors affecting their survival within the first 3 days of hospitalisation and survival after 3 days to hospital discharge.

STUDY DESIGN

Retrospective analysis of clinical records.

METHODS

Records of 148 horses admitted to the William R. Pritchard Veterinary Medical Teaching Hospital, University of California Davis from January 1995 to December 2010 with a history of recumbency or horses that became recumbent while hospitalised were evaluated. Exact logistic regression was used to assess the association between clinical parameters and survival within the first 3 days of hospitalisation and survival to hospital discharge after 3 days.

RESULTS

There were 109 nonsurvivors and 39 survivors. Multivariate analysis showed variables associated with an increased odds of death within the first 3 days of hospitalisation included duration of clinical signs prior to presentation, with horses showing clinical signs for over 24 h having increased odds of death (P = 0.043, odds ratio [OR] 4.16, 95% confidence interval [95% CI] 1.04-16.59), the presence of band neutrophils (P = 0.02, OR 7.94, 95% CI 1.39-45.46), the horse not using the sling (P = 0.031, OR 4.22, 95% confidence interval 1.14-15.68) and horses that were unable to stand after treatment (P<0.0001, OR 231.15, 95% CI 22.82-2341.33). Increasing cost was associated with lower odds of death (P = 0.017, OR 0.96, for each additional $100 billed, 95% CI 0.93-0.99).

CONCLUSIONS

This study demonstrates that the duration of clinical signs, response to treatment and the ability of horses to use a sling are associated with survival to hospital discharge for recumbent horses.