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Age and season affect serum testosterone concentrations in cryptorchid stallions
  1. A. Claes, DVM, DACT1,
  2. B. A. Ball, DVM, PhD, DACT1,
  3. C. J. Corbin, BS2 and
  4. A. J. Conley, BVSc, MRCVS, MS, PhD2
  1. 1Department of Veterinary Science, Gluck Equine Research Center, University of Kentucky, Lexington, KY 40546-0099, USA
  2. 2Department of Population Health and Reproduction, School of Veterinary Medicine, University of California Davis, Davis, CA 95616, USA
  1. E-mail for correspondence: ajconley{at}

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Cryptorchidism, characterised by inguinal and/or abdominal retention of one or both testes, is the most common developmental defect encountered in equine veterinary practice. Most cases present with stallion-like behaviour in males without palpable testes and questionable castration history. Evaluation of serum testosterone concentrations is commonly used to distinguish geldings from cryptorchid stallions without a scrotal testis, but results can be variable and difficult to interpret (Lu 2005, Raś and others 2010). Identifying factors that influence serum testosterone concentrations in cryptorchid stallions can be valuable in the interpretation of assay results. Both season and age are known to have a major effect on testosterone concentrations in intact stallions (Berndtson and others 1974, Raeside 1979, Stewart and Roser 1998), but little is known in cryptorchid stallions, with only one study reporting seasonal variation in serum testosterone concentrations (Cox and others 1988). Additionally, it is possible that serum testosterone concentrations in cryptorchid stallions are influenced by age as the cryptorchid testis is subjected to chronic elevated temperatures which could potentially adversely affect Leydig cell function. However, age-related changes in serum testosterone concentrations in cryptorchid stallions have not, to our knowledge, been described. Therefore, the objective of this study was to evaluate the effect of season and age on serum …

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