Survey of ocular abnormalities in draft horses

Objective

To determine the prevalence of ocular disease in draft horses in the United States.

Animals

Draft horses of various breeds and ages.

Procedure

Nondilated ophthalmic examination was performed using slit lamp biomicroscopy and indirect ophthalmoscopy. Intraocular pressures were measured when possible.

Results

One hundred sixty-five draft horses were examined. Age range: 10 days to 33 years (mean 10.8 years, median 10 years); 87 geldings (52.7%), 71 mares (43.0%), 7 stallions (4.2%); 64 Percherons (38.8%), 51 Belgians (30.9%), 29 Clydesdales (17.6%), 15 Shires (9%), and 6 other draft breed (3.6%). Intraocular pressure: mean 24.7 mmHg OD, range 13-37 mmHg; mean 25.0 mmHg OS, range 11-37 mmHg. Vision-threatening disease was present in 9 horses (5.5%): complete cataracts 1, post-traumatic optic nerve atrophy 1, uveitis and secondary glaucoma 1, retinal detachment 1, large chorioretinal scar 3, phthisis bulbi 2. Non-vision-threatening ocular disease was present in 56 horses (33.9%) involving one or more ocular structures: eyelid trauma/notch defect 14 (8.5%), SCC-type adnexal lesions 12 (7.3%), corneal scars 16 (9.7%), keratitis 6 (3.6%), corpora nigra cyst 15 (9.1%), incipient/punctate cataract 50 (30.3%), vitreous degeneration 10 (6.1%), asteroid hyalosis 1, “bullethole” chorioretinal scars 3, RPE coloboma 1. Linear keratopathy was present in 28 horses (17%) with 2/28 having concurrent vision threatening ocular disease.

Conclusions

Ocular abnormalities, in particular minor cataracts, were relatively common in this population, but not typically vision-threatening. Additionally, this survey demonstrated a greater prevalence of linear keratopathy in draft horses compared with reports in other breeds; however, it does not appear to be associated with concurrent ocular disease.     

Polysaccharide storage myopathy in Cob Normand draft horses

Gluteus medius muscle was sampled from 53 Cob Normand horses for histologic evaluation. Twenty horses (38%) exhibited amylase-resistant material in myocytes consistent with polysaccharide storage myopathy. Diameter of affected type II fibers was increased (67.7 +/- 21.4 microm) compared with normal ones (57.3 +/- 19.7 microm). Two groups were distinguished by quantitative study. The first group (n = 14; 26%) was characterized by a low percentage of fibers (m = 0.98%) containing aggregates occurring singly or in perifascicular clusters without myopathic changes. The second group (n = 6; 11%) was characterized by a high percentage (m = 18.1%) of fibers containing aggregates scattered in biopsy with chronic myopathic changes. Re-biopsy of 4 horses showed an increase with time in the number of aggregate-containing fibers for horses of the first group only. In 1 necropsied horse, aggregates were observed in a wide range of muscles including smooth muscles. Ultrastructurally, granular material was found interspersed among arrays of filamentous material.     

Reproductive performance and factors that decrease pregnancy rate in heavy draft horses bred at the foal heat

Reproductive performance and factors that decrease the pregnancy rate in heavy draft horses bred at the foal heat were investigated. The study was based on a total of 422 mares varying from 4 to 20 years in age, which had foaled during the period 1991 to 1994. Over the four years, the percentage of the mares bred at the foal heat was 62.6% and the pregnancy rate was 60.2%. The pregnancy rate following breeding at the foal heat in 1991 (67.7%) was significantly higher than that in 1992 (44.1%). Significant correlation was observed between the pregnancy rate and the mean placental retention time and also between the pregnancy rate and the mean temperature during the winter season. When compared on a monthly basis, the pregnancy rate following breeding at the foal heat in February was 53.3% and in May, 48.2%. The mean number of covers per mare at the foal heat was 2.3; this figure decreased to 1.8 for those bred in May. The mean number of days from parturition to the first breeding date was 11.3 days and the number of days from parturition to the last breeding day at the foal heat was 14.0 days. The number of days from parturition to the last breeding day at the foal heat decreased to 12.5 days in May. The latter may have been influenced by factors involving the stallion. When compared on a monthly basis, the mean placental retention time was longest in January (219 min.) following which it decreased gradually up to mid-summer. The mean placental retention time of mares which were not bred at the foal heat was significantly longer (197 min.) than in mares bred at the foaling heat (143 min.) and also in mares that conceived following breeding at the foal heat (135 min.). The pregnancy rate was less in mares bred shortly after parturition. The findings of this study would suggest that certain factors decrease the pregnancy rate in mares bred at the foal heat. The stress of low temperature in winter, prolonged placental retention time, breeding too early after parturition and factors pertaining to individual stallions may be involved. Expulsion of the placenta as soon as possible after foaling and appropriate breeding timing are significant factors that can influence the pregnancy rate following breeding at the foal heat.     

Airway inflammation in Michigan pleasure horses: prevalence and risk factors

REASONS FOR PERFORMING STUDY: Although subclinical airway inflammation is thought to be common in horses, there is little information on its prevalence and none on risk factors. OBJECTIVE: To determine the prevalence and risk factors for an increased number of inflammatory cells and for mucus accumulation in the trachea of pleasure horses. METHODS: Horses (n = 266) in stables (n = 21) in Michigan were examined endoscopically, once in winter and once in summer 2004. Visible tracheal mucoid secretions were graded 0-5 and inflammatory cell numbers counted in a tracheal lavage sample. Information collected about each horse included age, gender, presence of cough, percent time indoors and source of roughage. The repeated measures were analysed by generalised estimating equations and linear mixed models. RESULTS: Horses eating hay, especially from round bales, had the most neutrophils, whereas horses feeding from pasture had the fewest. Being female and being outdoors in winter were associated with increased numbers of inflammatory cells. Older horses had fewer macrophages than young horses. More than 70% of horses had >20% neutrophils in tracheal lavage. Twenty percent of horses had a mucus accumulation score >1; 17% had both a mucus score >1 and >20% neutrophils. The significant risk factors for mucus accumulation >1 were age >15 years, feeding on hay as compared to pasture, and being outdoors for more than 80% time in winter. Even though mucus accumulation score >1 was a risk factor for cough, only half of such horses coughed. Cough and mucus accumulation were associated with increased number of neutrophils. CONCLUSIONS: In comparison to pasture feeding, hay feeding, particularly from round bales, was associated with an increased number of neutrophils in the airway. Being outdoors in winter was associated with increased numbers of inflammatory cells and with mucus accumulation. Because 70% of horses have >20% neutrophils, this value should not be used as the sole indicator of airway inflammation. POTENTIAL RELEVANCE: The study reinforces the importance of hay feeding and older age as risk factors for inflammatory airway disease. Horses that do not have 'heaves' may be best kept indoors when winters are cold.     

A comparison of xylazine-ketamine and detomidine-ketamine anaesthesia in horses

Anaesthesia produced by xylazine (1.1 mg/kg IV) followed in 3–5 minutes by ketamine (2.2 mg/ kg IV) (X / K) was compared to anaesthesia produced by detomidine (0.02 mg/kg IV) followed in 15–25 minutes by ketamine (2.2 mg/kg IV) (D/K) in the same six horses. Quality of induction, recovery, muscle relaxation, coordination (before and after anaesthesia) and response to stimulus were subjectively evaluated. Heart rate, respiratory rate, mean blood pressure, hemoglobin saturation, arterial pH, CO₂ and O₂ were monitored. Recumbency time and number of attempts required to stand were recorded. Recumbency time was longer in all horses with X/K (median recumbency time of 27 min) than with D/K (median recumbency time of 22 min). No significant differences between treatments were seen for any other variable measured, although 2 horses did not appear to reach a surgical plane of anaesthesia with D/K.     

Climatic and aeroallergen risk factors for chronic obstructive pulmonary disease in horses

OBJECTIVE: To estimate the association between climate and airborne pollen and fungal factors and chronic obstructive pulmonary disease (COPD) in horses. SAMPLE POPULATION: Data from 1,444 horses with a diagnosis of COPD. PROCEDURE: The Veterinary Medical Database was used to identify records of horses admitted to veterinary teaching hospitals in the United States and Canada between 1990 and 1999. Rainfall, mean minimum and maximum temperature, and maximum monthly pollen and fungal spore (mold) counts recorded at the city closest to where the hospital is located were identified for each month data were reported to the Veterinary Medical Database. Associations between climatic and aeroallergen data and monthly prevalence of COPD were estimated by use of cross-correlation and logistic regression models. RESULTS: Significant positive correlations were found between prevalence of COPD and rainfall 3 months previously, minimum temperature 1 and 2 months previously, total pollen counts measured 3 months previously, and total mold counts measured during the same month and 1 month previously. CONCLUSIONS AND CLINICAL RELEVANCE: Outdoor aeroallergens and climatic factors may contribute to the occurrence of COPD in horses.     

Evaluation of intramuscular anesthetic protocols in healthy domestic horses

ObjectiveTo assess anesthetic induction, recovery quality and cardiopulmonary variables after intramuscular (IM) injection of three drug combinations for immobilization of horses.Study designRandomized, blinded, three-way crossover prospective design.AnimalsA total of eight healthy adult horses weighing 470–575 kg.MethodsHorses 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.ResultsAll 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 relevanceIn 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.     

Evaluation of dietary and management risk factors for enterolithiasis among horses in California

Enteroliths are intestinal calculi that result in intestinal obstruction and colic in horses. Equine enterolithiasis occurs worldwide, but the disease is particularly prevalent in some geographic locations, including California. The objectives of this study were to evaluate dietary and environmental risk factors for the disease. This was accomplished through a case–control study by comparing horses with colic from enterolithiasis presenting to the University of California, Davis VMTH, to horses with colic of other causes. Data were collected on 61 horses with enterolithiasis and 75 controls via evaluation of patient records and questionnaires completed by owners at the time of admission. Following multiple logistic regression analysis, the following factors were found to be significantly associated with enterolithiasis: feeding 50% of the diet as alfalfa; feeding <50% of the diet as oat hay; feeding <50% of the diet as grass hay; and lack of daily access to pasture grazing.     

Evaluation of dietary and management risk factors for enterolithiasis among horses in California

Enteroliths are intestinal calculi that result in intestinal obstruction and colic in horses. Equine enterolithiasis occurs worldwide, but the disease is particularly prevalent in some geographic locations, including California. The objectives of this study were to evaluate dietary and environmental risk factors for the disease. This was accomplished through a case–control study by comparing horses with colic from enterolithiasis presenting to the University of California, Davis VMTH, to horses with colic of other causes. Data were collected on 61 horses with enterolithiasis and 75 controls via evaluation of patient records and questionnaires completed by owners at the time of admission. Following multiple logistic regression analysis, the following factors were found to be significantly associated with enterolithiasis: feeding ⩾50% of the diet as alfalfa; feeding <50% of the diet as oat hay; feeding <50% of the diet as grass hay; and lack of daily access to pasture grazing.     

Dietary risk factors and colonic pH and mineral concentrations in horses with enterolithiasis

A prospective, unmatched case control study was performed to identify dietary and environmental risk factors for enterolithiasis in horses in California and to determine whether colonic ingesta analyses differed between horses with and without enteroliths. Forty-three horses with enterolithiasis were compared with 19 horses with surgical colic attributable to nonstrangulating obstruction of the colon without enteroliths. Colonic ingesta samples were collected at surgery from horses with enteroliths and control horses. Colonic pH and colonic concentrations of magnesium, phosphorus, sulfur, sodium, calcium, potassium, and nitrogen were measured. Questionnaires were distributed to owners to determine diet and management practices. Student's t-test and Mann-Whitney tests were used to evaluate differences in pH, dry matter content, percent nitrogen, and mineral content. Associations between dietary and management risk factors and enterolith occurrence were quantified by odds ratios. Mean pH of colonic contents from horses with enterolithiasis was significantly higher than for control horses. Horses with enterolithiasis had significantly lower percent dry matter in colonic fecal samples and higher mean mineral concentrations than controls. On the basis of reported feeding and management practices, horses with enterolithiasis were fed a significantly higher proportion of alfalfa in their diet and were less likely to have daily access to pasture grass than horses without enteroliths. Results suggest that decreasing alfalfa consumption and allowing daily access to pasture grazing might reduce the risk of enterolithiasis. Dietary modifications promoting acidification of colonic contents and dilution of minerals might be beneficial as preventive measures for enterolithiasis in horses.     

Bite and kick injuries in horses: prevalence, risk factors and prevention

REASON FOR PERFORMING STUDY: Studies on the prevalence and predisposing factors of bite and kick injuries in horses have not been reported in a population-based data sample. OBJECTIVES: To investigate the prevalence of bite and kick injuries in horses and associated risk factors in a representative sample of horses in Switzerland. METHODS: A questionnaire on the incidence of disease and injury, which included the frequency of bite and kick injuries and their association with breed, housing, use and feeding regime, was sent to 2559 horse owners randomly selected throughout Switzerland. RESULTS: The data of 2912 horses with 897 disorders diagnosed by a veterinarian were analysed. There were 231 injuries, 50 (21.6%) caused by a bite or kick from another horse; this number corresponded to 5.6% of all diseases and injuries and concerned only 1.7% of all the horses evaluated. Warmblood, Thoroughbred and Arabian horses had a 4.3 times higher risk of bite or kick injuries than horses of other breeds. Eighteen per cent of injuries were associated with a change in housing management and occurred regardless of whether horses were kept in groups permanently or sporadically. CONCLUSIONS AND POTENTIAL RELEVANCE: A stable group hierarchy and a housing system that provides adequate space and is adapted to horse-specific behaviour are important factors in prevention and kick and bite injuries.     

Evaluation of risk factors associated with development of postoperative ileus in horses

OBJECTIVE: To determine factors associated with development of postoperative ileus (POI) in horses undergoing surgery for colic. DESIGN: Prospective case-control study. ANIMALS: 251 horses undergoing colic surgery, of which 47 developed POI. PROCEDURE: Signalment, history, clinicopathologic data, pre- and postoperative treatments, lesions, complications, costs, and outcome were recorded for all horses during hospitalization. RESULTS: Variables associated with increased odds of POI included small intestinal lesion, high PCV, and increased duration of anesthesia. There was modest evidence that pelvic flexure enterotomy and intraoperative administration of lidocaine may have reduced the odds of developing POI. CONCLUSIONS AND CLINICAL RELEVANCE: Findings during the preoperative and intraoperative periods can be used to identify horses at increased risk of POI. Reducing surgical and anesthetic duration should decrease the incidence of POI.