Comparison of the navicular region of newborn foals and adult horses by magnetic resonance imaging

Magnetic resonance imaging (MRI) was tested for evaluation of the soft tissue structures of the equine digit in 16 limbs, derived from three adult warmblood horses and two newborn warmblood foals. The following measuring sequences were used in sagittal, transversal and coronal planes: spin echo, gradient echo, inversion recovery. The images were made with a 1.5 Tesla Siemens scanner in a CP-Helmholtz circular coil. To compare the visualization of the same tissue structures in adult and in newborn cases the limbs were imaged with the routinely used MRI sequences that are used for mature tissues. In newborn foals the bursa podotrochlearis could not be determined with the used sequences. For both the adult and newborn limbs the most visualization of the same tissue structures including the fluid spaces and growth plates were taken by the inversion recovery sequence. T2 sequence was very informative in adult cases but moderately in newborn foals.     

Electroencephalographic patterns of clinically normal, sedated, and tranquilized newborn foals and adult horses

To establish a clinically practical procedure for recording the equine EEG, 25 healthy adult horses and 6 newborn foals were used. Recordings were taken with the animals alert and tranquilized, confined in metal stocks, or physically restrained. The dominant alert waveforms of adult horses were fast activity (25 to 40 Hz) with medium-to-low voltages (5 to 40 microV-dominant 10 to 15 microV). Underlying this fast activity was slower (0.5 to 4.0 Hz) activity with medium-to-low voltages (10 to 40 microV). Twelve of the 25 adult horses had EEG frequencies in the alpha frequency range (10 to 15 Hz, 10 to 50 microV). Eight horses were given xylazine and 17 were given acetylpromazine. Those given xylazine had generalized slowing with several distinct frequency patterns (25 to 40 Hz, 5 to 30 microV; 10 to 15 Hz, 10 to 80 microV; and 0.5 to 4.0 Hz, 10 to 90 microV). Horses given acetylpromazine had fast activity (25 to 40 Hz) with medium-to-low voltages (5 to 40 microV). Underlying this activity were slower waveforms (1 to 4 Hz) with medium-to-low voltages (5 to 10 microV). Occasional well-formed spindle activity was observed (10 to 14 Hz, 10 to 50 microV). Acetylpromazine had little effect on the EEG recording, whereas xylazine exerted a substantial effect. All leads were synchronous with lower voltages in the left frontal, right frontal, and transfrontal leads. The alert pattern of a newborn foal was characterized by low frequency (2 to 6 Hz) with medium-to-high voltages (20 to 90 microV).(ABSTRACT TRUNCATED AT 250 WORDS)     

Pharmacokinetics of erythromycin in foals and in adult horses

The pharmacokinetic parameters of erythromycin in foals were determined following intravenous administration of 5.0 mg/kg to animals aged 1, 3, 5 and 7 weeks. The distribution of the drug was described by a two-compartment open model, and no significant differences were observed between coefficients on which the parameters were based. Pharmacokinetic values were also determined for four mares given 5.0 mg/kg intravenously and for six 10–12 week-old foals given 20.0 mg/kg intravenously. The half-life of erythromycin for all groups of animals (foals less than 7 weeks, mares, foals 10–12 weeks) was 1.0–1.1 h; the apparent volume of distribution was between 2.3 and 7.2 l/kg, and the clearance of the drug from the body was between 1.9 and 5.0 mg/kg/h. No drug could be detected in the serum following oral administration of 5.0 mg/kg erythromycin estolate; detectable levels were found for 5 h in mares given 12.5 mg/kg, and for 8 h in foals given 20.0 mg/kg orally. Peak levels in foals given the drug orally were 0.42 μg/ml at 120 min after administration. Foals given 10.0 mg/kg of erythromycin base intramuscularly had serum concentrations detectable 12 h later, the peak level achieved was 1.44 μg/ml serum 90 min after administration and concentrations exceeded 0.25 μg/ml for 6 h. In the mares the milk concentrations were approximately twice those in serum. Recommendations were made for drug dosage to be used in the treatment of Corynebacterium equi pneumonia of foals.     

Comparative pharmacokinetics of minocycline in foals and adult horses

The objective of this study was to compare the pharmacokinetics of minocycline in foals vs. adult horses. Minocycline was administered to six healthy 6‐ to 9‐week‐old foals and six adult horses at a dose of 4 mg/kg intragastrically (IG) and 2 mg/kg intravenously (i.v.) in a cross‐over design. Five additional oral doses were administered at 12‐h intervals in foals. A microbiologic assay was used to measure minocycline concentration in plasma, urine, synovial fluid, and cerebrospinal fluid (CSF). Liquid chromatography–tandem mass spectrometry was used to measure minocycline concentrations in pulmonary epithelial lining fluid (PELF) and bronchoalveolar (BAL) cells. After i.v. administration to foals, minocycline had a mean (±SD) elimination half‐life of 8.5 ± 2.1 h, a systemic clearance of 113.3 ± 26.1 mL/h/kg, and an apparent volume of distribution of 1.24 ± 0.19 L/kg. Pharmacokinetic variables determined after i.v. administration to adult horses were not significantly different from those determined in foals. Bioavailability was significantly higher in foals (57.8 ± 19.3%) than in adult horses (32.0 ± 18.0%). Minocycline concentrations in PELF were higher than in other body fluids. Oral minocycline dosed at 4 mg/kg every 12 h might be adequate for the treatment of susceptible bacterial infections in foals.     

Nondiarrheal disorders of the gastrointestinal tract in neonatal foals.

Neonates can have a variety of gastrointestinal disorders, primary and secondary in nature. Important primary disorders include con-genital abnormalities and meconium retention. One of the most important secondary lesions is generalized ileus. Gastric ulceration can occur as a primary or secondary event. This article addresses the pathophysiology, diagnosis, and treatment of gastrointestinal problems commonly observed in neonatal foals.     

Cochet-Bonnet aesthesiometer-determined corneal sensitivity in neonatal foals and adult horses

Corneal touch threshold (CTT) was measured in sick neonatal foals, healthy foals, and healthy adult horses with a Cochet-Bonnet aesthesiometer. The mean overall CTT for the adult horses, sick foals, and healthy foals was 4.82 +/- 0.87 cm, 3.21 +/- 0.24 cm, and 5.01 +/- 0.61 cm, respectively. The central cornea of adult horses was more sensitive than the limbal cornea. Corneal sensitivity was significantly reduced in sick neonatal foals compared to adults. The mean Schirmer I tear test values were significantly lower in foals than adults, and were 14.2 +/- 1.0 mm, 12.8 +/- 2.4 mm, and 18.3 +/- 2.1 mm wetting in sick neonatal foals, normal neonatal foals, and adult horses, respectively. Reduced corneal sensation and lower tear production may be associated with ulcerative keratitis and slow corneal healing in some foals.     

Lung surfactant function and composition in neonatal foals and adult horses

BACKGROUND: Lung surfactant function and composition are varied and adapted to the specific respiratory physiology of all mammalian species. HYPOTHESIS: Lung surfactant function and composition are different in neonatal foals as compared to adult horses. ANIMALS: Six adult horses, 7 term foals (<24 hours old), and 4 premature foals were used. Animals were part of the Auburn University teaching herd except for 3 client-owned premature foals. METHODS: Bronchoalveolar lavage fluid (BALF) was obtained from all animals. Ultracentrifugation of cell-free BALF separated surfactant into crude surfactant pellets (CSP) and supernatant. Both fractions were analyzed for phospholipid and protein content with the Bartlett and bicinchoninic acid method, respectively. Phospholipid composition of the CSP was determined by using high-performance liquid chromatography with an evaporative light scatter detector. Surface tension of the CSP was measured with a pulsating bubble surfactometer. Results from term foals (<24 hours old) were compared statistically to those from adult horses. Values of P < .05 were considered significant. RESULTS: BALF phospholipid content was similar between adult horses and term foals, but BALF protein content was significantly decreased in term foals. Phosphatidylglycerol was significantly decreased, phosphatidylinositol was significantly increased, and the minimum surface tension was significantly increased in the CSP from term foals compared to adult horses. CONCLUSIONS AND CLINICAL IMPORTANCE: Surface tension and phospholipid composition of surfactant in neonatal foals are significantly different compared to adult horses. These changes may influence biophysical and immunologic functions of surfactant.     

Detection of apoptotic cells in intestines from horses with and without gastrointestinal tract disease

OBJECTIVE: To identify apoptosis in equine intestines and determine whether apoptosis is associated with gastrointestinal tract disease or a specific tissue layer of intestine. ANIMALS: 38 horses that underwent surgery or were euthanatized for small or large intestine obstruction, strangulation, or distension and 9 control horses euthanatized for reasons other than gastrointestinal tract disease or systemic disease. PROCEDURE: Specimens were collected at surgery from intestine involved in the primary lesion and distant to the primary lesion site or at necropsy from several sites including the primary lesion site. Histologic tissue sections were stained with H&E, and apoptosis was detected by use of the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling technique. The number of apoptotic cells per hpf was counted in the mucosa, circular muscle, longitudinal muscle, and serosa. RESULTS: Apoptotic nuclei were seen in all layers of intestine. An increased number of apoptotic cells was found in the circular muscle of the intestine from horses with simple obstruction, compared with strangulating obstruction or healthy intestine. Intestine distant from a primary strangulating lesion had higher numbers of apoptotic cells than did intestine distant from a simple obstructive lesion or intestine taken at the site of a strangulating or simple obstructive lesion. CONCLUSIONS AND CLINICAL RELEVANCE: Intestine from horses with obstructing or strangulating lesions in the small intestine and large colon had high numbers of apoptotic cells possibly because of ischemic cell injury and subsequent inflammation. Whether substantial apoptosis affects intestinal function is not yet known.     

Diarrhea associated with sand in the gastrointestinal tract of horses

Four horses with diarrhea had radiographic evidence of large quantities of sand in the gastrointestinal tract. Initially, none of the horses had sufficient fecal sand quantity to suggest sand enteropathy. Diarrhea resolved in all horses within 2 days of oral administration of psyllium hydrophilic mucilloid. Historically, all 4 horses had lost weight or had difficulty maintaining weight. After treatment was administered, the horses either gained weight or were easier to maintain in good condition.     

Cervical spinal kinematics: a comparison between foals and adult horses

A photographic method was used to measure axial rotation, dorsoventral flexion and extension and lateral bending at each intervertebral joint complex from the occiput to the first thoracic vertebra in spinal segments from 19 foals under 12 months of age and 14 horses over three years of age. Comparisons between the two groups showed that there was a general reduction in cervical spinal mobility with age. For the three types of movement at the eight joints tested, adults' mobility exceeded that of foals in only three cases (axial rotation and lateral bending at the A-O joint, and lateral bending at C7-T1). These differences were not significant (P greater than 0.05). In the remaining 21 cases the amplitude of movement was greater in the foals, the differences being significant (P less than 0.05) in 16 cases. With regard to overall mobility of the cervical spine the foals exceeded the adults by 17.3 per cent for axial rotation, 22.0 per cent for dorsoventral flexion and extension and 18.7 per cent for lateral bending.     

Histologic findings in the gastrointestinal tract of horses with colic

Thirty horses were admitted to the University of Georgia Veterinary Medical Teaching Hospital with colic severe enough to warrant surgery and/or euthanasia. Gastrointestinal tracts of these 30 horses were histologically examined for morphologic changes. The horses were grouped according to cause of the colic (ie, simple obstruction, strangulation obstruction, thromboemboli, and inflammation). Lesions were graded as to severity, and grade scores were correlated with survival or nonsurvival. Mucosal changes developed distal and proximal to the primary lesion site and, although there were some differences between groups, changes characteristic of ischemia were common to all groups. The predictability of lesion grades of 2 or higher for nonsurvivability (90%) indicates that intestinal biopsy may have prognostic value in the postsurgical evaluation and management of equine colic.     

Characterization of Clostridium perfringens in the feces of adult horses and foals with acute enterocolitis

Up to 60% of cases of equine colitis have no known cause. To improve understanding of the causes of acute colitis in horses, we hypothesized that Clostridium perfringens producing enterotoxin (CPE) and/or beta2 toxin (CPB2) are common and important causes of severe colitis in horses and/or that C. perfringens producing an as-yet-undescribed cytotoxin may also cause colitis in horses. Fecal samples from 55 horses (43 adults, 12 foals) with clinical evidence of colitis were evaluated by culture for the presence of Clostridium difficile, C. perfringens, and Salmonella. Feces were also examined by enzyme-linked immunosorbent assay (ELISA) for C. difficile A/B toxins and C. perfringens alpha toxin (CPA), beta2 toxin (CPB2), and enterotoxin (CPE). Five C. perfringens isolates per sample were genotyped for the following genes: cpa, cpb, cpb2 consensus, cpb2 atypical, cpe (enterotoxin), etx (epsilon toxin), itx (iota toxin), netB (necrotic enteritis toxin B), and tpeL (large C. perfringens cytotoxin). The supernatants of these isolates were also evaluated for toxicity for an equine cell line. All fecal samples were negative for Salmonella. Clostridium perfringens and C. difficile were isolated from 40% and 5.4% of samples, respectively. All fecal samples were negative for CPE. Clostridium perfringens CPA and CPB2 toxins were detected in 14.5% and 7.2% of fecal samples, respectively, all of which were culture-positive for C. perfringens. No isolates were cpe, etx, netB, or tpeL gene-positive. Atypical cpb2 and consensus cpb2 genes were identified in 15 (13.6%) and 4 (3.6%) of 110 isolates, respectively. All equine C. perfringens isolates showed far milder cytotoxicity effects than a CPB-producing positive control, although cpb2-positive isolates were slightly but significantly more cytotoxic than negative isolates. Based on this studied population, we were unable to confirm our hypothesis that CPE and CPB2-producing C. perfringens are common in horses with colitis in Ontario and we failed to identify cytotoxic activity in vitro in the type A isolates recovered.     

Mean platelet component as an indicator of platelet activation in foals and adult horses

BACKGROUND: Mean platelet component (MPC) is a new platelet variable, measured by modern commercial complete blood count analyzers, that is reduced during platelet activation in humans and small animals. HYPOTHESIS: MPC decreases in horses with clinical conditions that cause platelet activation and disseminated intravascular coagulation (DIC). ANIMALS: We obtained 418 CBCs from 100 sick and 20 healthy neonates and 178 sick and 45 sound adult horses. Sick neonates were classified into septic and nonseptic, and DIC and non-DIC groups. Adults were grouped by diagnoses (systemic inflammatory disorders, gastrointestinal problems, and thrombocytopenia). METHODS: MPC together with platelet count, mean platelet volume, platelet distribution width, and platelet component distribution width were measured with a commercial analyzer and compared between the different disease and control groups in neonates and in adults. RESULTS: MPC values were significantly lower in the septic and nonseptic neonates (24.0 +/- 3.5 g/dL and 26.6 +/- 2.6 g/dL, respectively) than in the control group (28.1 +/- 1.7 g/dL). Neonates with DIC had the lowest MPC values (23.8 +/- 6.3 g/dL). MPC values in adult horses were significantly lower in the inflammatory (23.5 +/- 4.7 g/dL), gastrointestinal obstruction (23.0 +/- 5.0 g/dL), enteritis (23.6 +/- 4.6 g/dL), ischemic (23.9 +/- 5.1 g/dL), and thrombocytopenia (20.2 +/- 5.7 g/dL) groups when compared with control horses (26.2 +/- 3.5 g/dL). Other platelet variables were not different between the control and the disease groups. CONCLUSION AND CLINICAL IMPORTANCE: MPC might be a useful variable for quickly and easily detecting platelet activation in sick neonates and adult horses.     

Detection of respiratory herpesviruses in foals and adult horses determined by nested multiplex PCR

A nested multiplex PCR was developed as a rapid (<12h), sensitive test for the simultaneous identification of equine herpesviruses (EHV1, EHV4, EHV2 and EHV5) in clinical samples from horses. Peripheral blood and nasal swab (NS) samples from 205 weanling Thoroughbred foals on 6 different studs over 3 consecutive seasons and from 92 adult horses without clinical signs of respiratory disease were examined using direct multiplex PCR of clinical samples (direct PCR) and conventional cell culture with differentiation of EHV in cell cultures by multiplex PCR. Multiplex PCR proved a sensitive and specific technique for the detection of EHV in cell culture and clinical samples. The technique described appeared equally sensitive as one using a single set of primers for individual EHV but reduced labour and reagent costs. Cell cultures showing cytopathic effect (CPE) were always positive for EHV on PCR. EHV were also detected by multiplex PCR in 11 samples which failed to show CPE. By a combination of multiplex PCR and cell culture or direct multiplex PCR, the presence of up to three EHV in the same sample was detected. Overall, EHV5 was detected by direct multiplex PCR of peripheral blood mononuclear cells (PBMC) and/or NS samples from 78% of foals and 47% of adult horses. Repeated sampling or cell culture in combination with multiplex PCR and with the incorporation of IL-2 in culture medium increased the sensitivity for detection of EHV in PBMC and demonstrated that EHV5 DNA could be identified in PBMC from 89% of foals and 100% of adult horses. EHV2 was identified from approximately 30% of foals, but was more frequently identified in samples from 17 foals with mild respiratory disease and was isolated infrequently from adult horses. EHV1 and EHV4 were identified uncommonly in any population in the current study.     

Diagnosis and management of thyroid disorders and thyroid hormone supplementation in adult horses and foals

Equine thyroid disorders pose a diagnostic challenge in clinical practice because of the effects of nonthyroidal factors on the hypothalamic–pituitary–thyroid axis, and the horse's ability to tolerate wide fluctuations in thyroid hormone concentrations and survive without a thyroid gland. While benign thyroid tumours are common in older horses, other disorders like primary hypothyroidism or hyperthyroidism in adult horses and congenital hypothyroidism in foals are rare. There is a common misunderstanding regarding hypothyroidism in adult horses, especially when associated with the clinical profile of obesity, lethargy, and poor performance observed in dogs and humans. Low blood thyroid hormone concentrations are often detected in horses as a secondary response to metabolic and disease states, including with the nonthyroidal illness syndrome; however, it is important to note that low thyroid hormone concentrations in these cases do not necessarily indicate hypothyroidism. Assessing equine thyroid function involves measuring thyroid hormone concentrations, including total and free fractions of thyroxine (T4) and triiodothyronine (T3); however, interpreting these results can be challenging due to the pulsatile secretion of thyroid hormones and the many factors that can affect their concentrations. Dynamic testing, such as the thyrotropin-releasing hormone stimulation test, can help assess the thyroid gland response to stimulation. Although true hypothyroidism is extremely rare, thyroid hormone supplementation is commonly used in equine practice to help manage obesity and poor performance. This review focuses on thyroid gland pathophysiology in adult horses and foals, interpretation of blood thyroid hormone concentrations, and evaluation of horses with thyroid disorders. It also discusses the use of T4 supplementation in equine practice.     

Liver biopsy techniques for adult horses and neonatal foals to assess copper status

Objective To evaluate standing, percutaneous, ultrasound-guided, transthoracic liver biopsy in mares, and transabdominal, laparoscopically-guided, liver biopsy under general anaesthesia in foals, as techniques for obtaining tissue for assessment of copper status. The techniques were evaluated with respect to ease of use and effect on the animal.
Procedure Twenty of 24 Thoroughbred mares and 21 of their foals were biopsied. The animals were part of a larger study of the effect of copper supplementation on copper status and the prevalence of developmental orthopaedic disease. Livers were also collected from unrelated horses and sampled to investigate the variability in the distribution of copper in liver tissue.
Result The biopsy technique caused no lasting effect on the mares, but there was an increased risk of viscus penetration associated with taking multiple biopsy cores. The use of ultrasonography to scan the target area for the liver identified four cases that were not appropriate candidates for liver biopsy, because of large intestine being located in the biopsy area. In the foals there were no serious postoperative adverse effects, nor was there any evidence of problems caused by the procedure when the abdomen was examined post-mortem at 5 months of age. In livers collected to investigate the variability of copper concentration, copper appeared to be relatively evenly distributed through the liver.
Conclusion Standing, percutaneous, ultrasound-guided, transthoracic liver biopsy in mares, and transabdominal, laparoscopically-guided, liver biopsy under general anaesthesia in foals are convenient procedures for obtaining liver tissue for assessing copper status in horses. The use of ultrasound to identify liver tissue is recommended, especially in older mares.     

Influence of bacitracin on microbial functions in the gastrointestinal tract of horses

This study investigated the influence of zinc bacitracin on the intestinal flora of horses. The functionally active intestinal flora was examined in 6 horses during treatment with zinc bacitracin. Utilising gas chromatography, spectrophotometry, gel electrophoresis and paper chromatography, samples were analysed on biochemical markers reflecting the action of parts of the intestinal flora. The following 5 flora-related functions were studied in faecal samples and intestinal samples from different sections of the hindgut: conversion of cholesterol to coprostanol and of bilirubin to urobilinogens, degradation of mucin and of beta-aspartylglycine and inactivation of tryptic activity. Conversion to coprostanol, conversion to urobilinogens and degradation of mucin were affected by treatment of zinc bacitracin and conversion to coprostanol was most sensitive. All functions were normalised in a short time, in contrast to man and rats. Differences in environmental exposures are probably the reason for a more rapid normalisation of the intestinal flora functions in horses.     

Mucosal distribution of eosinophilic granulocytes within the gastrointestinal tract of horses

OBJECTIVES: To establish reference values for the range of the number of eosinophils found in equine gastrointestinal mucosa and to describe the distribution of this cell within the equine gastrointestinal mucosa. SAMPLE POPULATION: Gastrointestinal mucosal specimens from 14 adult horses euthanatized for reasons other than gastrointestinal disease. PROCEDURES: Gastrointestinal mucosal specimens were collected and grouped according to their anatomic regions. For histologic examination slides were stained with Luna's eosinophil stain to determine eosinophil accumulation and distribution. The mucosa was divided into 5 sections for each anatomic location, and the percentage of eosinophils in each of the 5 sections relative to the total eosinophil count in all sections was determined. Additionally, the number of eosinophils per square millimeter of mucosa was calculated as a measure of the degree of eosinophil accumulation. RESULTS: Lowest numbers of eosinophils were found in the stomach, and numbers increased from there to the cecum, then decreased from the ascending colon (right ventral colon, left ventral colon, pelvic flexure, left dorsal colon, and right dorsal colon) to small colon. In all gastrointestinal sections, most eosinophils were located near the muscularis mucosae and were rarely found near or on the luminal surface of the mucosa. CONCLUSIONS AND CLINICAL RELEVANCE: The distribution of eosinophils in the gastrointestinal tract of horses followed a pattern within the mucosa and between different sections of the gastrointestinal tract. The derived reference values and distribution data could be used to detect changes in eosinophil response in the equine gastrointestinal mucosa caused by diseases states.