Effect of weight loading on the coronary band interstitial fluid pressure in horses

Interstitial fluid pressures, as a possible function of limb load, were measured at 2 sites within the digital coronary dermis of both cranial digits in 10 standing horses. Fluid pressure changes and digital load measurements were simultaneously detected and recorded by use of, respectively, modified wick-in-needle and force plate transducers coupled to a microcomputer. Mean pressures, recorded at limb loads between 50 and 80 kg, were 2.29 +/- 3.17 mm of Hg at the toe and 2.49 +/- 5.91 mm of Hg at the heel. Mean pressures, recorded between 150 and 180 kg, were 5.01 +/- 5.23 mm of Hg at the toe and 1.28 +/- 7.69 mm of Hg at the heel. These data indicate that, in the static limb, no statistically significant change in interstitial fluid pressure occurs at loads up to 180 kg.     

Keratin and associated proteins of the equine hoof wall.

In this study, we described water-insoluble proteins extracted from the germinative regions (stratum internum and coronary band epithelium) and the cornified outer surface (stratum medium) of the equine hoof wall. Two major types of polypeptides were identified: the intermediate filaments (IF) and the IF-associated proteins. The IF, including keratins, composed a major portion of this fraction, had electrophoretic mobilities on sodium dodecyl sulfate-polyacrylamide gel electrophoresis in the range of 40 to 80 kDa, and reacted with acidic or basic keratin-specific monoclonal antibodies. Differences in the composition of keratins between germinative layers and the stratum medium were seen. Another less well-characterized group of polypeptides associated with the IF also were extracted with the water-insoluble polypeptide fraction. These associated proteins had an apparent molecular weight between 10 and 30 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and contained a higher percentage of sulfur-containing amino acids than did the IF. Water-insoluble protein fractions compared favorably with those found in other less-specialized keratinizing tissue with respect to size, immunoreactivity with monoclonal antibody, and amino acid composition.     

Development of Immunologic Assays to Measure Response in Horses Vaccinated with Xenogeneic Plasmid DNA Encoding Human Tyrosinase

Xenogeneic plasmid DNA constructs have been developed and optimized for immunotherapies targeting cancer in both humans and dogs. Specifically, plasmid vectors containing the tumor antigen tyrosinase have demonstrated immunoreactivity and clinical benefit in the treatment of melanocytic tumors in these species. Overexpression of tyrosinase has also been noted in equine melanocytic tumors, supporting its role as a valid tumor antigen in the horse. Vaccination with plasmid constructs containing tyrosinase may thus have translational immunoreactivity in the treatment of equine melanomas. Here, we describe a methodology that is highly sensitive and specific for the detection of both humoral and cell-mediated immunoreactivity against tyrosinase in equine patients. These antigen-specific immunoassays are used to measure the humoral and cell-mediated responses in a cohort of horses vaccinated with xenogeneic plasmid DNA encoding human tyrosinase. Serum humoral responses were measured using standard enzyme-linked immunosorbent assay technique against the full-length recombinant human tyrosinase protein. Peripheral blood mononuclear cells were collected from vaccinated horses and stimulated with tyrosinase-specific peptides. Cell-mediated responses were then measured using a novel quantitative real-time-polymerase chain reaction technique to determine resultant interferon-γ expression. All horses developed significantly positive humoral and cell-mediated immune responses compared with their individual prevaccination values. No adverse reactions or signs of autoimmunity were detected. Vaccination with xenogeneic plasmid DNA expressing tyrosinase appears to elicit tumor antigen-specific reactivity and should be evaluated in a larger cohort of horses with melanocytic tumors.     

The pharmacokinetics of furosemide in anaesthetized horses after bilateral ureteral ligation

The pharmacokinetics of furosemide were investigated in anaesthetized horses with bilateral ureteral ligation (BUL) with ( n  = 5) or without ( n  = 5) premedication with phenylbutazone. Horses were administered an intravenous (i.v.) bolus dose of furosemide (1 mg/kg) 6090 min after BUL. Plasma samples collected up to 3 h after drug administration were analysed by a validated high performance liquid chromatography method. Median plasma clearance ( CL _p) of furosemide in anaesthetized horses with BUL was 1.4 mL/min/kg. Apparent steady state volume of distribution ( V d_ss) ranged from 169 to 880 mL/kg and the elimination half life ( t _½) ranged from 83 min to 209 h.   No differences in plasma concentration or kinetic parameter estimates were observed when phenylbutazone was administered before furosemide administration. BUL markedly reduces the elimination of furosemide in horses and models the potential effects that severe changes in kidney function may have on drug kinetics in horses.     

The Role of Vascular Mechanisms in the Development of Acute Equine Laminitis

ACUTE LAMINITIS has long been attributed to factors or events that precede the onset of laminitis. Between 1759 and 1907 the overconsumption of grain, inflammation of the feet, suppression of perspiration (anhydrosis), excessive rest, excessive bleeding, road concussion, poor shoeing, unilateral weight bearing, sudden environmental temperature changes, prolonged standing (in the cold and aboard ships), diarrhea, and postpartum complications were all designated as causes. Today, commonly listed etiologic factors include ingestion of large amounts of grain, cold water, lush grass, or black walnut shavings, repeated concussion, endometritis or other severe infections, colic, exhaustion, stress, drug toxicities, and endocrine dysfunctions. At Texas A&M University (Table 1) the factors recorded as the cause presume a causal relationship between some preceding event and the acute laminitis. Logically, any event that precedes laminitis might be a cause, but etiologic validity depends on the definition of "cause" and the role that coincidence might have in the appearance of the disease.     

Absorbance Spectra of Inter-Species Hemoglobins in the Visible and Near Infrared Regions

This study was initiated to determine if the absorbance spectra of hemoglobins from nonhuman species were sufficiently different from those of human hemoglobin to affect the applicability of pulse oximetry to common domestic species. Hemoglobin was isolated from the blood of humans, dogs, cats, horses, cows, and pigs. The millimolar extinction coefficients for oxygenated and deoxygenated hemoglobin samples were determined over the wavelength range of 600 to 1000 nm. Minor differences in the absorbance of both oxyhemoglobin and deoxyhemoglobin were found between human hemoglobin and that of the dog, cat, horse, cow, and pig. However, correction for the presence of methemoglobin, the effects of light scattering by impurities in the solution, and technical error rendered these differences statistically insignificant. The results of this study suggest that the spectral properties of canine, feline, equine, bovine, and porcine hemoglobin do not differ significantly from that of human hemoglobin and should not be a limiting factor in the application of pulse oximeters that are based on human algorithms to animal species.     

Evaluation of Needle-free Injection Devices for Intramuscular Vaccination in Horses

Needle-free injection devices have been approved for the delivery of biologics with inherently low immunogenicity, such as plasmid DNA vaccines; however, no studies have described their use in equine patients. This article compares the use of two such devices (VitaJet-3 and Biojector2000) at typical vaccination sites in a cohort of six horses. After identifying the optimal device and vaccination site, a second cohort of five horses was used to document the biologic activity of a DNA plasmid vector delivered with the selected injector. Injector characteristics, including the amount of intramuscular drug deposition, residual skin dose, and pain responses, were evaluated following vaccination, with colored saline in the pectoral muscles and cervical region in six horses. The optimal device was then selected and used for intramuscular vaccination with the pING/tyrosinase plasmid vector in a group of five horses. Biological activity was measured through antibody response to the protein encoded by the plasmid on days 0, 14, 28, 42, and 56 postvaccination. Optimal intramuscular dose delivery was obtained in the pectoral muscle site using the VitaJet-3. No significant pain responses were noted. Dependent edema was seen at vaccination sites 24 hours after therapy. Antibody responses to the protein encoded by the DNA plasmid vector significantly increased after vaccinations in all horses. The VitaJet-3 is easy to use and is effective for delivering intramuscular vaccinations with DNA plasmid vectors in horses. This device allows for vaccination with vectors that exhibit low immunogenicity and/or that require targeted delivery to specific tissue planes.     

The digital pathologies of chronic laminitis.

This review indicates that the patient-to-patient uniqueness commonly seen in chronic laminitis represents the variable presence of the digital pathologies. Although some degree of mechanical failure is always present, the secondary metabolic and growth dysplasias, vascular pathologies, and sepsis may or may not be evident. The presence and severity of these pathologies appear to have a more significant impact on the prognosis of individual cases than does the displacement of the distal phalanx. It should be reiterated that it is often the combined presence of these individual pathologies that gives rise to the patient that is totally refractory to treatment. In the absence of these pathologies, many horses with significant displacement of the distal phalanx are not in pain and are not in need of treatment. It thus follows that a key to the improved rehabilitation of difficult patients is focusing research on the physiopathology and diagnosis of these nonmechanical problems.     

Protection from challenge following administration of a canarypox virus-vectored recombinant feline leukemia virus vaccine in cats previously vaccinated with a killed virus vaccine

OBJECTIVE: To compare protection against FeLV challenge obtained following administration of 2 doses of an adjuvanted, chemically inactivated, whole FeLV (FeLV-k) vaccine with protection obtained following administration of 1 dose of an FeLV-k vaccine followed by 1 dose of a canarypox virus-vectored recombinant FeLV (rCP-FeLV) vaccine. DESIGN: Prospective study. ANIMALS: Thirty-two 9-week-old domestic shorthair cats. PROCEDURE: Cats received 2 doses of the FeLV-k vaccine SC, 21 days apart (n = 11); 1 dose of the FeLV-k vaccine SC and, 21 days later, 1 dose of the rCP-FeLV vaccine transdermally (11); or 2 doses of physiologic saline (0.9% NaCl) solution (control; 10). Four weeks after the second vaccine dose, all cats were challenged with FeLV by means of oronasal administration. Blood samples were collected at weekly intervals beginning 21 days after challenge, and serum was tested for FeLV antigen. RESULTS: All 10 control cats became persistently infected (ie, FeLV antigen detected in > or = 3 consecutive serum samples) following FeLV challenge, whereas only 1 of 11 cats that received 2 doses of the FeLV-k vaccine and none of the 11 cats that received 1 dose of the FeLV-k vaccine and 1 dose of the rCP-FeLV vaccine did. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that protection against FeLV challenge obtained following SC administration of a single dose of an FeLV-k vaccine followed, 21 days later, by transdermal administration of a single dose of an rCP-FeLV vaccine was similar to that obtained following SC administration of 2 doses of the FeLV-k vaccine 21 days apart.