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  • Author or Editor: Irwin K. M. Liu x
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Objective—To characterize the activity of catalase in equine semen.

Animals—15 stallions of known and unknown reproductive history.

Procedure—Seminal plasma was collected from raw equine semen by centrifugation, and samples of seminal plasma were frozen prior to assay for catalase activity. Tissue samples (n = 3 stallions) from the bulbourethral gland, prostate gland, vesicular gland, and testis were homogenized, and cauda epididymal fluid was collected for determination of catalase activity. Catalase activity was determined as an enzyme kinetic assay by the disappearance of H2O2 as measured by ultraviolet spectrophotometry.

Results—Catalase activity in equine seminal plasma was 989.3 ± 167.8 U/ml (mean ± SEM), and the specific activity of catalase in equine seminal plasma was 98.7 ± 29.2 U/mg of protein. Specific activity of catalase in tissue homogenates was significantly higher in the prostate gland (954 ± 270 U/mg of protein) than in the ampulla (59 ± 5 U/mg of protein), bulbourethral gland (54 ± 11 U/mg of protein), vesicular gland (39 ± 3 U/mg of protein), cauda epididymal fluid (11 ± 3 U/mg protein), or testis (54 ± 6 U/mg of protein).

Conclusions and Clinical Relevance—Equine seminal plasma contains a high activity of catalase that is derived primarily from prostatic secretions. Procedures such as semen cryopreservation that remove most seminal plasma from semen may reduce the ability to scavenge H2O2 and thereby increase the susceptibility of spermatozoa to oxidative stress. (Am J Vet Res 2000;61:1026–1030)

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in American Journal of Veterinary Research


Objective—To test a hypothesis predicting that isoflurane would interfere with cerebrovascular autoregulation in horses and to evaluate whether increased mean arterial blood pressure (MAP) would increase cerebral blood flow and intracranial pressure (ICP) during isoflurane anesthesia.

Animals—6 healthy adult horses.

Procedures—Horses were anesthetized with isoflurane at a constant end-tidal concentration sufficient to maintain MAP at 60 mm Hg. The facial, carotid, and dorsal metatarsal arteries were catheterized for blood sample collection and pressure measurements. A sub-arachnoid transducer was used to measure ICP Fluorescent microspheres were injected through a left ventricular catheter during MAP conditions of 60 mm Hg, and blood samples were collected. This process was repeated with different-colored microspheres at the same isoflurane concentration during MAP conditions of 80 and 100 mm Hg achieved with IV administration of dobutamine. Central nervous system tissue samples were obtained after euthanasia to quantify fluorescence and calculate blood flow.

Results—Increased MAP did not increase ICP or blood flow in any of the brain tissues examined. However, values for blood flow were low for all tested brain regions except the pons and cerebellum. Spinal cord blood flow was significantly decreased at the highest MAP.

Conclusions and Clinical Relevance—Results suggested that healthy horses autoregulate blood flow in the CNS at moderate to deep planes of isoflurane anesthesia. Nonetheless, relatively low blood flows in the brain and spinal cord of anesthetized horses may increase risks for hypoperfusion and neurologic injury.

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in American Journal of Veterinary Research


Objective—To test the hypothesis that head-down positioning in anesthetized horses increases intracranial pressure (ICP) and decreases cerebral and spinal cord blood flows.

Animals—6 adult horses.

Procedures—For each horse, anesthesia was induced with ketamine hydrochloride and xylazine hydrochloride and maintained with 1.57% isoflurane in oxygen. Once in right lateral recumbency, horses were ventilated to maintain normocapnia. An ICP transducer was placed in the subarachnoid space, and catheters were placed in the left cardiac ventricle and in multiple vessels. Blood flow measurements were made by use of a fluorescent microsphere technique while each horse was in horizontal and head-down positions. Inferential statistical analyses were performed via repeated-measures ANOVA and Dunn-Sidak comparisons.

Results—Because 1 horse developed extreme hypotension, data from 5 horses were analyzed. During head-down positioning, mean ± SEM ICP increased to 55 ± 2 mm Hg, compared with 31 ± 2 mm Hg during horizontal positioning; cerebral perfusion pressure was unchanged. Compared with findings during horizontal positioning, blood flow to the cerebrum, cerebellum, and cranial portion of the brainstem decreased significantly by approximately 20% during head-down positioning; blood flows within the pons and medulla were mildly but not significantly decreased. Spinal cord blood flow was low (9 mL/min/100 g of tissue) and unaffected by position.

Conclusions and Clinical Relevance—Head-down positioning increased heart-brain hydrostatic gradients in isoflurane-anesthetized horses, thereby decreasing cerebral blood flow and, to a greater extent, increasing ICP. During anesthesia, CNS regions with low blood flows in horses may be predisposed to ischemic injury induced by high ICP.

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in American Journal of Veterinary Research


Objective—To determine the incidence of equine herpesvirus-1 (EHV-1) infection among Thoroughbreds residing on a farm on which the virus was known to be endemic.

Design—Prospective cohort study.

Animals—10 nonpregnant mares, 8 stallions, 16 weanlings, 11 racehorses, and 30 pregnant mares and their foals born during the 2006 foaling season.

Procedures—Blood and nasopharygeal swab samples were collected every 3 to 5 weeks for 9 months, and placenta and colostrum samples were collected at foaling. All samples were submitted for testing for EHV-1 DNA with a PCR assay. A type-specific EHV-1 ELISA was used to determine antibody titers in mares and foals at birth, 12 to 24 hours after birth, and every 3 to 5 weeks thereafter.

Results—Results of the PCR assay were positive for only 4 of the 1,330 samples collected (590 blood samples, 590 nasopharyngeal swab samples, 30 placentas, and 30 colostrum samples), with EHV-1 DNA detected in nasal secretions from 3 horses (pregnant mare, stallion, and racehorse) and in the placenta from 1 mare. Seroconversion was detected in 3 of 27 foals during the first month of life.

Conclusions and Clinical Relevance—Results suggested that there was a low prevalence of EHV-1 infection among this population of Thoroughbreds even though the virus was known to be endemic on the farm and that pregnant mares could become infected without aborting. Analysis of nasopharyngeal swab samples appeared to be more sensitive than analysis of blood samples for detection of EHV-1 DNA.

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in Journal of the American Veterinary Medical Association