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  • Author or Editor: L. L. Blythe x
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SUMMARY

An oral vitamin E absorption test used in human beings was modified for use in horses. The most appropriate techniques with which to measure gastrointestinal tract absorption of vitamin E (α-tocopherol) in horses were developed. Vitamin E was administered orally, and serum values of α-tocopherol were measured by use of high-performance liquid chromatography at 0, 3, 6, 9, 12, and 24 hours after vitamin E administration. Variables included comparison of 2 dosages (45 and 90 IU/kg of body weight), routes of administration, and absorption dynamics of 3 preparations of dl-α-tocopherol. Absorption of the 2 doses of dl-α-tocopherol acetate indicated a dose response; the area under the curve at 24 hours (AUC24) was 4.3 μg-h/ ml for the 45-IU/kg dose and 32.2 μg-h/ml (P < 0.01) for the 90-IU/kg dose. Maximal absorption was apparent when vitamin E was naturally consumed in grain, compared with administration of identical preparations by stomach tube or paste. In the same horses, dl-α-tocopherol and dl-α-tocopherol acetate plus polyethylene glycol had statistically similar absorption curves and both had significantly greater AUC24, compared with dl-α-tocopherol acetate; values for the 3 compounds were 23.6, 25.8, and 12.6 μg-h/ml, respectively. The AUC24 varied between individual horses, but time of peak value was consistently observed between 6 and 9 hours.

On the basis of the data from this study, the recommended technique for performing the oral vitamin E absorption test in horses would be administration of 90 IU of the free form of dl-α-tocopherol/kg, mixed in 1 L of grain to horses from which food has been withheld for 12 hours, followed by allowing the horses ad libitum access to hay immediately after administration of the vitamin E. Three baseline serum α-tocopherol values should be obtained within 24 hours prior to the test, with the last sample being obtained just prior to administration of the test dose of vitamin E. Heparinized plasma also may be used for this testing procedure. α-Tocopherol concentration should be measured at 3, 6, 9, 12, and 24 hours after vitamin E administration.

Free access
in American Journal of Veterinary Research

SUMMARY

Plasma α-tocopherol (vitamin E) values were monitored serially in 9 foals sired by a stallion with equine degenerative myeloencephalopathy (EDM) and in 5 agematched control foals (sired by a clinically normal stallion) raised in the same environment for the first year of life. Clinical evaluation determined that 8 of the 9 foals sired by the stallion with EDM had neurologic deficits consistent with the disease on one or more occasions during the study period, whereas control foals had normal gait. From 6 weeks to 10 months of age, plasma α-tocopherol values in foals with signs of EDM were significantly (P < 0.001) lower than those in control foals. An oral vitamin E absorption test was performed, and results for 8 of the affected horses and the affected stallion were compared with results for 4 of the monitored control horses and 4 additional control horses. Significant differences were not evident in any of the absorption indices. On the basis of data from this study and supported by reported prophylactic and therapeutic benefits of supplemented vitamin E, low plasma concentration of vitamin E is concluded to be a factor in the development of EDM in the first year of life of hereditarily predisposed foals. It was also concluded that the significantly lower α-tocopherol values seen in the foals in this study did not reflect a primary gastrointestinal tract absorption problem.

Free access
in American Journal of Veterinary Research
in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association

Summary

Recent evidence concerning the pathogenesis of equine degenerative myeloencephalopathy indicated that low blood α-tocopherol values are a factor in the disease process. Variables that could be introduced by a veterinarian procuring, transporting, or storing samples were evaluated for effects on α-tocopherol concentration in equine blood. These variables included temperature; light; exposure to the rubber stopper of the evacuated blood collection tube; hemolysis; duration of freezing time, with and without nitrogen blanketing; and repeated freeze/thaw cycles. It was found that hemolysis caused the greatest change in high-performance liquid chromatography-measured serum α-tocopherol values, with mean decrease of 33% (P < 0.001). Lesser, but significant (P < 0.01) changes in serum α-tocopherol values were an approximate 10% decrease when refrigerated blood was left in contact with the red rubber stopper of the blood collection tube for 72 hours and an approximate 5% increase when blood was stored at 20 to 25 C (room temperature) for 72 hours. Repeated freeze/thaw cycles resulted in a significant (P < 0.05) 3% decrease in α-tocopherol values in heparinized plasma by the third thawing cycle. Freezer storage for a 3-month period without nitrogen blanketing resulted in slight (2%) decrease in mean serum α-tocopherol values, whereas values in serum stored for an identical period under nitrogen blanketing did not change. A significant (P < 0.001) mean decrease (10.3%) in α-tocopherol values was associated with freezer (− 16 C) storage of nitrogen blanketed serum for 6 months. Comparison of α-tocopherol values in serum vs heparinized plasma vs edta-treated plasma resulted in serum values being significantly (P < 0.001) higher (approx 4%) than values in either type of plasma. It was concluded that the optimal method for storing equine blood samples prior to α-tocopherol analysis is in an upright position in a refrigerator for up to 72 hours. If a longer period is needed prior to analysis, it is recommended that the serum or plasma be separated from blood, blanketed with nitrogen gas, and frozen in the smallest possible vial. The α-tocopherol in these samples should be stable at − 16 C for at least 3 months.

Free access
in American Journal of Veterinary Research

Objective

To determine seroprevalence of antibodies to Sarcocystis neurona in neurologically normal horses residing in 4 regions of Oregon and to describe the effects of age, gender, breed, and housing on seroprevalence within each region.

Design

Prevalence survey.

Sample Population

Serum samples from 334 horses systematically selected by practicing veterinarians.

Procedure

Antibodies to S neurona were measured in sera, using a western blot. Information including age, gender, breed, housing, geographic location, and duration of residence was obtained for each horse. Data were analyzed, using descriptive statistics.

Results

45% (149/334) of horses evaluated were seropositive for antibodies to S neurona with significant differences in the percentage of seropositive horses from different regions of the state. Seroprevalances of antibodies to S neurona in horses in regions I and II, west of the Cascade Range, were 65 and 60%, respectively; whereas seroprevalances in central and eastern Oregon, regions III and IV, were 43 and 22%, respectively. Seroprevalence consistently increased with age of horse for each region.

Gender, breed, and housing were not associated with significant differences in seroprevalence of antibodies to S neurona in the overall sample population, or in comparisons of samples obtained from horses within a particular region, or among samples obtained from horses residing in different regions.

Clinical Implications

The high seroprevalence of antibodies to S neurona in neurologically normal horses indicates that analysis of serum alone would not be useful for definitive diagnosis of equine protozoal myeloencephalitis in horses in Oregon. (J Am Vet Med Assoc 1997;210:525–527)

Free access
in Journal of the American Veterinary Medical Association

Summary

A clinical, viral, hematologic, and genetic study was conducted over a 4-year period on a family of Appaloosas with high incidence of clinical ataxia and pathologic features of equine degenerative myeloencephalopathy. Marginal to deficient serum vitamin E (α-tocopherol) and blood selenium values were the only other consistent antemortem abnormalities in the affected horses. Members of this family were all descendants of a clinically normal mare and were raised in 3 separate environments with variable quality of feed. All horses had access to pasture grasses. Normal chromosomal karyotypes were found in 11 affected and/or related horses examined. Equine herpesvirus type 2 was isolated from 4 of the horses, but evidence for a role of this virus in the pathogenesis of the disease was not found. The role of antioxidant deficiency in the pathogenesis of neurologic dysfunction in this equine family and in others reported to be affected with equine degenerative myeloencephalopathy remains speculative.

Free access
in Journal of the American Veterinary Medical Association
in Journal of the American Veterinary Medical Association