Browsing by Author "McKenzie, H. C."

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    Equine neonatal sepsis: The pathophysiology of severe inflammation and infection
    McKenzie, H. C.; Furr, M. O. (Veterinary Learning Systems, 2001-07-01)
    Although the clinical syndrome of sepsis is a major problem in equine neonates, the pathophysiology of this condition remains incomplete. Because the term sepsis describes a broad range of disorders with different underlying causes and often different prognoses, the understanding of this process is further complicated. Continued progress is being made, how- ever, in defining the syndromes associated with sepsis and in elucidating the mechanisms in- volved in these processes. Attempts at modulating the septic process by interfering with the action of bacterial toxins or the production or activity of individual mediators have not been successful, thereby reinforcing that this is a multifactorial response. Fortunately, the complex interactions of intra- and extracellular messengers leading to clinical sepsis continue to be defined. An increased understanding of the processes involved in the septic response may aid in the identification of patients with these syndromes as well as improve the effectiveness of treatment regimens.
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    Evaluating digestibility and toxicity of native warm-season grasses for equines
    Ghajar, Shayan; McKenzie, H. C.; Fike, John H.; McIntosh, B.; Tracy, B. F. (2021-01)
    Introduced cool-season grasses are dominant in Virginia's grasslands, but their high digestible energy and nonstructural carbohydrate (NSC) levels pose a risk for horses prone to obesity and laminitis. Native warm-season grasses (NWSGs) have lower digestible energy and NSC levels that may be more suitable for horses susceptible to laminitis. Although NWSGs have desirable characteristics, they are novel forages for horses. Little is known about NWSG intake or potential toxicity to horses or how grazing by horses may affect NWSG swards. The overall objectives of this research were to 1) assess voluntary intake, toxicological response, and apparent digestibility of NWSG hays fed to horses; and 2) evaluate the characteristics of three NWSG species under equine grazing. For the first objective, a hay feeding trial using indiangrass (IG) (Sorghastrum nutans) and big bluestem (BB) (Andropogon gerardii) was conducted with nine Thoroughbred geldings in a replicated 3 x 3 Latin square design. Voluntary dry matter intake of IG and BB hays by horses were 1.3% and 1.1% of BW/d, lower than orchardgrass (Dactylis glomerata), an introduced cool-season grass, at 1.7% of BW/d (P = 0.0020). Biomarkers for hepatotoxicity remained within acceptable ranges for all treatments. Apparent dry matter digestibility (DMD) did not differ among hays, ranging from 39% to 43%. NSC levels ranged from 4.4% to 5.4%, below maximum recommended concentrations for horses susceptible to laminitis. For the second objective, a grazing trial was conducted comparing IG, BB, and eastern gamagrass (EG) (Tripsacum dactyloides) yields, forage losses, changes in vegetative composition, and effects on equine bodyweight. Nine, 0.1-ha plots were seeded with one of the three native grass treatments, and each plot was grazed by one Thoroughbred gelding in two grazing bouts, one in July and another in September 2019. IG had the greatest available forage, at 4,340 kg/ha, compared with 3,590 kg/ha from BB (P < 0.0001). EG plots established poorly, and had only 650 kg/ha available forage during the experiment. Grazing reduced standing cover of native grasses in IG and BB treatments by about 30%. Horses lost 0.5-1.5 kg BW/d on all treatments. Findings suggest IG and BB merit further consideration as forages for horses susceptible to obesity and pasture-associated laminitis.
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    Glucocorticoid Receptor Density and Binding Affinity in Healthy Horses and Horses with Systemic Inflammatory Response Syndrome
    Hoffman, C. J.; McKenzie, H. C.; Furr, M. O.; Desrochers, A. (Wiley-Blackwell, 2015-03-01)
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    Immunogenicity of Potomac horse fever vaccine when simultaneously co-administered with rabies vaccine in a multivalent vaccine or as two monovalent vaccines at separate sites
    McKenzie, H. C.; Funk, Rebecca A.; Trager, L.; Werre, Stephen R.; Crisman, Mark V. (Wiley, 2019-11-01)
    Background: Potomac horse fever (PHF) is a potentially fatal enterocolitis of horses caused by Neorickettsia risticii. The disease was originally recognised almost 40 years ago in the state of Maryland in the US. It is now known to occur in many areas of North America, as well as having been described in South America and Europe. Monocomponent PHF vaccines are available, but clinical protection with vaccination has been reported to be inconsistent. Objectives: This study was designed to assess the immunogenicity of a commercially available Potomac Horse Fever (PHF) vaccine when administered as either a monovalent PHF vaccine simultaneously co-administered with a separate monovalent Rabies vaccine or as a multivalent PHF/Rabies vaccine in horses. Study design: Randomised parallel group trial. Methods: Ninety-one client or University owned horses participated in this open-label randomised study, with 45 horses receiving the monovalent vaccines at separate sites and 46 receiving the multivalent vaccine at a single site. Serum PHF IFA titres were determined twice prior to vaccination and at 1, 2 and 3 months after vaccination. Results: Both vaccination protocols exhibited poor immunogenicity, with only one-third of all the animals demonstrating seroconversion, defined as an increase in titre of greater than 400 over baseline, at any time point after vaccination. The monovalent PHF vaccine exhibited significantly greater immunogenicity in terms of the number of horses exhibiting seroconversion, as compared to the multivalent vaccine, at one (20 vs. 11, P = 0.03) and two (18 vs. 9, p = 0.02) months post vaccination. The monovalent PHF vaccine also exhibited significantly greater immunogenicity in terms of the median (interquartile range) IFA titres, as compared to the multivalent vaccine, at one (800 [200–1600] vs. 400 [200–800], P = 0.009) and 2 months (400 [200–1600] vs. 400 [100–800], P = 0.02) post vaccination. There was no significant difference between groups at 3 months in either seroconversion rate or median IFA titers. Main limitations: This study did not assess the actual protective effects of PHF vaccination but rather used the serologic response to vaccination as a surrogate biomarker of immunity. Conclusions: The multivalent PHF/Rabies vaccine exhibited lower immunogenicity as compared to the monovalent PHF vaccine co-administered with a separate Rabies vaccine.