**8. The usefulness of transthyretin in veterinary medicine**

Despite the physiological importance of transthyretin in health and as disease marker, there are only a few studies analysing its usefulness in the clinical and laboratory diagnosis of diseases in animals. Studies performed in dogs suggested that not only quantitative but also qualitative differences exist between human and canine TTR [97]. Transthyretin from dog plasma was of lower molecular mass compared to human TTR in samples subjected to sodium dodecyl-polyacrylamide gel electrophoresis with subsequent Western blot analysis [98]. Piechotta et al. [99] investigated the serum concentrations of TTR in dogs with nonthyroidal illness (including neoplasia, allergy, cardiac disease, gastrointestinal disease, parasitism and hepatic disease) and low T4 concentrations compared with those in healthy dogs and dogs with primary hypothyroidism. They found significantly decreased serum concentrations of TTR in dogs with nonthyroidal illness (24.8 mg/L) compared with its concentration in hypothyroid dogs (41.1 mg/L). On the other hand, significant differences in TTR values were not found between hypothyroid and healthy dogs, or between dogs with nonthyroidal illness and healthy dogs. In the study presented by Raila et al. [100], low concentration of TTR was found in a young dog with chronic renal failure, probably caused by its increased urinary excretion. Changes in the serum concentrations of TTR were observed also in rats during proteinenergy malnutrition [62]. The mean value of transthyretin in healthy pig serum obtained by Campbell et al. [54] was 302 ± 8 mg/L, but following *Streptococcus suis* type 2 infection the concentrations markedly decreased. In horses, transthyretin was identified using immunodiffusion technique, but the study was performed many years ago [101]. Establishing a quantitative method, such as an enzyme immunoassay, to measure the concentrations of TTR may be useful also in horses. In cattle, there are very little published reports about the usefulness of transthyretin in the diagnosis of diseases. Our preliminary results suggest lower concentrations of TTR in diarrhoic calves at the age of 1 month compared with healthy animals at the same age. Similarly, *Mycobacterium avium paratuberculosis* seropositive cows showed lower TTR values than those obtained in healthy cattle (unpublished data). Chang et al. [102] have isolated and sequenced transthyretin not only in humans and other mammalian species but also in birds, including emu, chicken, ostrich and pigeon. This study showed that TTR has greater than 98% homology and has a very similar binding pattern across species. However, additional studies should be done to determine the effect of various diseases on the serum concentrations of TTR in animals.
