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To evaluate applicability of a human osteocalcin (OC) immunoradiometric assay (IRMA) for use with equine serum and compare it with a bovine radioimmunoassay (RIA) previously proven valid for such samples, and to describe the effect of type and breed of horses on serum OC concentration.


100 healthy horses of either sex, classified as type I or II (draught or warmblood, respectively). Each type was represented by 2 breed groups, each comprising 25 horses.


Blood samples were collected in the morning, and the serum was separated. Osteocalcin was measured, using commercially available RIA and IRMA kits, according to the manufacturer's instructions. All samples were evaluated in duplicate.


The human IRMA did not recognize equine OC. Significant variations in the bovine RIA results were observed between types of horses. Draught horses had lower OC concentration, compared with warmblood horses. Significant difference was not observed between breeds for type of horse. Sex had no influence on serum OC values, but age was a significant covariable for both types of horses.


No crossreactivity exists between the equine and human amino- and/or carboxy-terminus of OC, using this particular human IRMA kit. Difference in blood OC concentration exists between draught and warmblood types of horses.

Clinical Relevance

Use of this human IRMA kit is not valid for equine serum. Horse type must be taken into account when evaluating OC concentration in research or clinical situations, especially if small variations in OC concentration are expected. (Am J Vet Res 1997;58:574–578)

Free access
in American Journal of Veterinary Research


Objective—To investigate whether volumetric capnography indices could be used to differentiate between horses without recurrent airway obstruction (RAO) and horses with RAO that were in clinical remission or that had clinically apparent RAO.

Animals—70 adult Swiss Warmblood horses (20 used for pleasure riding and 50 used for dressage or show jumping).

Procedure—Horses were allocated to 4 groups on the basis of history, clinical signs, results of endoscopy, and cytologic findings (group 1, 21 healthy horses; group 2, 22 horses with RAO that were in remission; group 3, 16 horses with mild RAO; group 4, 11 horses with exacerbated RAO). Expiratory volume and CO2 curves were recorded by use of a computerized ultrasonic spirometer. Volumetric capnograms were plotted, and derived indices were calculated.

Results—Dead-space volume (VD) was calculated by use of the Bohr equation (VDBohr) and for physiologic VD (VDphys). Ratios for VDBohr to expiratory tidal volume (VT) and VDphys to VT as well as an index of effective CO2 elimination were significantly different among groups of horses. Age and use of the horses also significantly affected volumetric capnography indices.

Conclusions and Clinical Relevance—Ratios of VDBohr to VT and VDphys to VT as well as an index of effective CO2 elimination were sufficiently sensitive measures to distinguish between healthy horses and horses with RAO in remission. To optimize the ability of volumetric capnography indices to differentiate among horses in heterogeneous populations, it is important to account for effects of age and specific use of the horses. (Am J Vet Res 2003;64:338–345)

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in American Journal of Veterinary Research