Elevated urinary excretion of free pyridinoline in Friesian horses suggests a breed-specific increase in collagen degradation

Background: Friesian horses are known for their high inbreeding rate resulting in several genetic diseases such as hydrocephaly and dwarfism. This last decade, several studies focused on two other presumed hereditary traits in Friesian horses: megaoesophagus and aortic rupture. The pathogenesis of these diseases remains obscure but an important role of collagen has been hypothesized. The purpose of this study was to examine possible breed-related differences in collagen catabolism. Urinary specimens from Friesian (n = 17, median age 10 years old) and Warmblood horses (n = 17, median age 10 years old) were assessed for mature collagen cross-links, i.e. pyridinoline (PYD) (=hydroxylysylpyridinoline/HP) and deoxypyridinoline (DPD) (lysylpyridinoline /LP). Solid-phase extraction was performed, followed by reversed-phase ion-paired liquid chromatography prior to tandem mass spectrometry (MS/MS) detection. Results: Mean urinary concentrations of free PYD, expressed as fPYD/creatinine ratio, were significantly higher in Friesian horses compared to Warmblood horses (28.5 ± 5.2 versus 22.2 ± 9.6 nmol/mmol, p = 0.02) while mean fDPD/creatinine ratios were similar in both horse breeds (3.0 ± 0.7 versus 4.6 ± 3.7 nmol/mmol, p = 0.09). Conclusions: Since DPD is considered a specific bone degradation marker and PYD is more widely distributed in connective tissues, the significant elevation in the mean PYD/DPD ratio in Friesian versus Warmblood horses (9.6 ± 1.6 versus 5.7 ± 1.8, p < 0.0001) suggests a soft tissue origin for the increased fPYD levels. Considering that a previous study found no differences in total collagen content between Friesian and Warmblood horses for tendon and aortic tissue, this indicates a higher rate of collagen degradation. The latter might, at least in part, explain the predisposition of Friesians to connective tissue disorders

Comparison between radiography and computed tomography for diagnosis of equine skull fractures

The equine head is a complex structure prone to traumatic injuries. To determine the value and limitations of radiography and (CT) for the diagnosis of skull fracture, the differences between the two modalities were described. Two observers retrospectively reviewed the radiographic and CT images of 18 horses with a skull fracture. To allow direct comparison between the two modalities, a simplified fracture classification system was used. In 3/18 cases the evaluation of the radiographic examination concluded no injuries visible. In 2/15 cases soft tissue involvement was not detected and in 7/15 cases the extension of the fracture was underestimated with radiography. Radiography classified 4/10 multiple fractures incorrectly as single fracture and 5/15 comminuted fractures on CT were diagnosed as simple fracture with radiography. The number of fragments was underestimated with radiography in 14/15 cases. In conclusion, radiography is able to diagnose a skull fracture in most cases. Skull fractures however are not similarly classified after radiographic and CT evaluation, which causes a difference in interpretation and perception of the fractures. Therefore, CT should be the modality of choice for surgical planning and prognosis