Search Results

You are looking at 21 - 28 of 28 items for

  • Author or Editor: Stephanie J. Valberg x
  • Refine by Access: All Content x
Clear All Modify Search

Abstract

Objective—To evaluate whether biochemical or genetic alterations in AMP-activated protein kinase (AMPK) play a role in the development of polysaccharide storage myopathy (PSSM) in Quarter Horses.

Animals—30 PSSM-affected and 30 unaffected (control) Quarter Horses.

Procedures—By use of an established peptide phosphotransfer assay, basal and maximal AMPK activities were measured in muscle biopsy samples obtained from 6 PSSM-affected and 6 control horses. In 24 PSSM-affected and 24 control horses, microsatellite markers identified from the chromosomal locations of all 7 AMPK subunit genes were genotyped with a fluorescent DNA fragment analyzer. Alleles of 2 of the AMPK γ subunit genes were genotyped via DNA sequencing. Allele frequencies of DNA markers in or near the AMPK subunit genes were measured in isolated genomic DNA.

Results—No differences in basal or maximal muscle AMPK enzyme activities between PSSM-affected and control horses were detected. There were also no differences in allele frequencies for microsatellite markers near any of the 7 AMPK subunit genes between the 2 groups. Furthermore, previously known and newly identified alleles of 2 equine AMPK γ subunit genes were also not associated with PSSM.

Conclusions and Clinical Relevance—These results have provided no evidence to indicate that AMPK plays a causative role in PSSM in American Quarter Horses.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether there was genetic linkage between the recurrent exertional rhabdomyolysis (RER) trait in Thoroughbred horse pedigrees and DNA markers in genes (the sarcoplasmic reticulum calcium release channel [RYR1] gene, the sarcoplasmic reticulum calcium ATPase [ATP2A1] gene, and the transverse tubule dihydropyridine receptor-voltage sensor [CACNA1S] gene) that are important in myoplasmic calcium regulation.

Animals—34 horses in the University of Minnesota RER resource herd and 62 Thoroughbreds from 3 families of Thoroughbreds outside of the university in which RER-affected status was assigned after 2 or more episodes of ER had been observed.

Procedures—Microsatellite DNA markers from the RYR1, ATP2A1, and CACNA1S gene loci on equine chromosomes 10, 13, and 30 were identified. Genotypes were obtained for all horses in the 4 families affected by RER, and data were used to test for linkage of these 3 loci to the RER phenotype.

Results—Analysis of the RYR1, CACNA1S, and ATP2A1 microsatellites excluded a link between those markers and the RER trait.

Conclusions and Clinical Relevance—It is likely that the heritable alterations in muscle contractility that are characteristic of RER are caused by a gene that is not yet known to cause related muscle disease in other species.

Full access
in American Journal of Veterinary Research

Abstract

Objective—To characterize clinical findings, outcomes, muscle characteristics, and serum or muscle concentrations of α-tocopherol for horses with vitamin E–responsive signs of muscle atrophy and weakness consistent with signs of equine motor neuron disease (EMND).

Design—Retrospective case-control study.

Animals—8 affected (case) adult horses with acute (n = 3) or chronic (5) gross muscle atrophy that improved with vitamin E treatment and 14 clinically normal (control) adult horses with adequate (within reference range; 8) or low (6) muscle concentrations of α-tocopherol.

Procedures—Medical records were reviewed, serum and muscle concentrations of α-tocopherol were measured, and frozen biopsy specimens of sacrocaudalis dorsalis medialis muscle and gluteal muscle were histologically evaluated for pathological changes. Fiber type composition and fiber diameters were assessed in gluteal muscle specimens.

Results—A myopathy that was histologically characterized by redistribution of mitochondrial enzyme stain (moth-eaten appearance) and anguloid atrophy of myofibers was evident in sacrocaudalis dorsalis medialis muscle fibers of the 8 affected horses that had low serum (6/8) or skeletal muscle (5/5) concentrations of α-tocopherol; these histopathologic changes were not found in muscle specimens of control horses with low or adequate muscle concentrations of α-tocopherol. All affected horses regained strength and muscle mass within 3 months after initiation of vitamin E treatment and dietary changes.

Conclusions and Clinical Relevance—A vitamin E–deficient myopathy characterized histologically by a moth-eaten appearance in the mitochondria and anguloid myofiber atrophy in frozen sections of sacrocaudalis dorsalis medialis muscle biopsy specimens was found in horses with clinical signs of EMND that were highly responsive to vitamin E treatment. This myopathy may be a specific syndrome or possibly precede the development of neurogenic muscle fiber atrophy typical of EMND.

Restricted access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To determine daily variation in urinary clearance and fractional excretion (FE) of electrolytes and minerals within and between horses and to compare volumetric and single-sample urine collection for determining FE values of diets with a range of dietary cation-anion balance (DCAB).

Animals—5 Thoroughbred and 6 mixed-breed mares.

Procedure—3 isocaloric diets with low, medium, and high DCAB values (85, 190, and 380 mEq/kg of dry matter, respectively) were each fed for 14 days. Daily blood samples, single urine samples collected by using a urinary catheter (5 mares), and volumetric urine collections (6 mares) were obtained during the last 72 hours of each diet.

Results—Urine and plasma pH values, plasma concentrations, and FE values of sodium, chloride, potassium, magnesium, phosphorus, and calcium were altered by varying the DCAB. Noticeable variation in clearance and FE values was detected within horses from day-to-day on the same diet as well as between horses. Fractional excretion values were not significantly different between single-sample and volumetric methods, except for magnesium in the high DCAB diet. Volumetric and single-sample collections revealed similar patterns of change in urinary FE values with varying DCAB, except for calcium and magnesium.

Conclusions and Clinical Relevance—Substantial variation in clearance and FE of electrolytes and minerals are evident within horses between 24-hour periods as well as between horses fed a specific diet. Three daily urine samples provide similar information regarding dietary-induced changes in clearance and FE values (excluding calcium and magnesium) as that obtained by volumetric urine collection. (Am J Vet Res 2003;64:284–291)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To determine whether plasma, urine, and fecal electrolyte and mineral concentrations differ between clinically normal horses and Thoroughbreds with recurrent exertional rhabdomyolysis (RER) after consumption of diets varying in cation-anion balance.

Animals—5 Thoroughbred mares with RER and 6 clinically normal mixed-breed mares.

Procedure—Each of 3 isocaloric diets designated as low, medium, and high on the basis of dietary cationanion balance (DCAB) values of 85, 190, and 380, respectively, were fed to horses for 14 days. During the last 72 hours, 3 horses with RER and 3 control horses had daily urine and fecal samples obtained by total 24-hour collection. Remaining horses had urine samples collected daily by single catheterization.

Results—For each diet, no differences existed between horses with RER and control horses in plasma pH, electrolyte concentrations, and creatine kinase activity or in urine pH and renal fractional excretion (FE) values. Plasma pH, strong ion difference, bicarbonate and total carbon dioxide concentrations, and base excess decreased and plasma chloride and ionized calcium concentrations increased with decreasing DCAB. Urine pH decreased with decreasing DCAB. The FE of chloride and phosphorus were greatest for horses fed the low diet. The FE values for all electrolytes exept magnesium did not differ between urine samples obtained by single catheterization and total 24-hour collection. Daily balance of calcium, phosphorus, sodium, chloride, and potassium did not differ significantly among horses fed the various diets.

Conclusions—In clinically normal horses and in horses with RER, the DCAB strongly affects plasma and urine pH and the FE of sodium, potassium, chloride, and phosphorus. (Am J Vet Res 2002;63:1053–1060)

Full access
in American Journal of Veterinary Research

Abstract

Objective—To estimate allele frequencies of the hyperkalaemic periodic paralysis (HYPP), lethal white foal syndrome (LWFS), glycogen branching enzyme deficiency (GBED), hereditary equine regional dermal asthenia (HERDA), and type 1 polysaccharide storage myopathy (PSSM) genes in elite performance subgroups of American Quarter Horses (AQHs).

Design—Prospective genetic survey.

Animals—651 elite performance AQHs, 200 control AQHs, and 180 control American Paint Horses (APHs).

Procedures—Elite performance AQHs successful in 7 competitive disciplines (barrel racing, cutting, halter, racing, reining, western pleasure, and working cow horse) were geno- typed for 5 disease-causing alleles. Age-matched control AQHs and APHs were used to establish comparative whole-breed estimates of allele frequencies.

Results—Highest allele frequencies among control AQHs were for type 1 PSSM (0.055) and GBED (0.054), whereas HERDA (0.021) and HYPP (0.008) were less prevalent. Control APHs uniquely harbored LWFS (0.107) and had high prevalence of HYPP (0.025), relative to AQHs. Halter horse subgroups had significantly greater allele frequencies for HYPP (0.299) and PSSM (0.155). Glycogen branching enzyme deficiency, HERDA, and PSSM were found broadly throughout subgroups; cutting subgroups were distinct for HERDA (0.142), and western pleasure subgroups were distinct for GBED (0.132). Racing and barrel racing subgroups had the lowest frequencies of the 5 disease genes.

Conclusions and Clinical Relevance—Accurate estimates of disease-causing alleles in AQHs and APHs may guide use of diagnostic genetic testing, aid management of genetic diseases, and help minimize production of affected foals.

Restricted access
in Journal of the American Veterinary Medical Association

Abstract

Objective—To develop a diagnostic test for recurrent exertional rhabdomyolysis (RER) in Thoroughbreds that relied on in vitro contracture of muscle biopsy specimens and determine whether the inheritance pattern of RER diagnosed on the basis of this contracture test was consistent with an autosomal dominant trait.

Design—Clinical trial.

Animals—8 adult horses with RER and 16 control adult horses for development of the contracture test; 23 foals for inheritance of RER.

Procedure—External intercostal muscle biopsy specimens from the 24 adult horses were tested for contracture in response to halothane and caffeine, and criteria for a positive test result were determined. These criteria were then applied to results for the 23 foals to determine whether they had RER. Simple segregation analysis was performed to determine whether results were consistent with a dominant pattern of inheritance.

Results—Results of the contracture test were positive for 5 of the 12 colts and 4 of the 11 fillies. Results of segregation analysis were consistent with an autosomal dominant pattern of inheritance. Two sires with RER produced colts with RER, supporting the hypothesis that RER had an autosomal, rather than an X-linked, inheritance pattern. In addition, in 1 instance, an unaffected colt was produced by 2 affected parents, which was not consistent with a recessive mode of inheritance.

Conclusions and Clinical Relevance—Although the expression of the RER trait is influenced by sex, temperament, and diet, among other factors, results from the in vitro muscle contracture test and this breeding trial suggest that RER in Thoroughbreds can be modeled as a genetic trait with an autosomal dominant pattern of inheritance. ( J Am Vet Med Assoc 2005;227:762–767)

Restricted access
in Journal of the American Veterinary Medical Association