Aging of the prostate in dogs : part II: Changes of prostatic size in breeds with different longevity

Introduction and aim. The overall median longevity of the general dog population is 11-12 years (1,2). Longevity in crossbred dogs exceeds that of purebred dogs by 1.2 years and increasing bodyweight is negatively correlated with life expectancy (2). Dogs of different breeds get geriatric at different ages because of different breed’s expected longevity (2,3). Small-breed dogs (such as small terriers) become geriatric at about 11 years, whereas giant-breed dogs (such as Great Danes) at 7 years. It is well known that prostate gland may develop benign prostatic hyperplasia in dogs over 5 years (4), and senile involution might occur in aged dogs (5). The purpose of the present study was to estimate whether changes of the prostatic size are related to the geriatric phase typical of the breed (based on life expectancy) or to the mean age of geriatric dogs. Materials and methods. Intact male dogs (n=612) of different breed, age (1-18 years) and bodyweight (2-55 kg), irrespective of the reason of clinical examination, underwent to ultrasonographic evaluation of the prostate. Length (L), width (W), and height (H) were measured (8C-RS 6-10MHz probe, Vivid i, GE Medical Systems Israel Ltd, Tirat Carmel, Israel) and prostatic volume was estimated using the ellipsoid formula L x W x H x 0.523 (6). Prostate size was considered as normal, enlarged or small according to the literature (7). Dogs were divided in two groups based on breeds’ life expectancy (1,2): S and L (short and long life, respectively). All dogs of both groups were further divided into subgroups based on different geriatric age typical of the breeds: S1 <7 years> S2 and L1 <11 years> L2 (3). Mean age of old dogs in group S was 10 years, and in group L was 13 years. Changes of prostate size as a consequence of being in the geriatric phase of life, or as a consequence of the mean age of geriatric dogs were assessed by Chi-Square test (p<0.05). Results. A total of 229 and 383 dogs were allocated in group S (S1: n=98 and S2: n=131) and in group L (L1: n=244 and L2: n=139), respectively. An enlarged prostate was observed more frequently in dogs of geriatric age (S2 38% and L2 54%), than in younger dogs (S1 7% and L1 32%), p<0.0001). In group S2 only few dogs (5%) presented a prostate of small size and this result was not different (p>0.05) from that obtained in S1 dogs (0%), whereas in group L higher proportions of old dogs (L2: 12%) showed a decrease in size compared to L1 dogs (1%; p<0.0001). The mean age of geriatric dogs significantly affected the results. An enlarged or small prostate was more frequently observed in dogs of group L2, than in those of group S2 (enlarged: 54% vs. 38% p<0.01; small: 12% vs. 5%; p<0.05). Conclusions. The results above confirm that the geriatric phase of the dog’s life (>7 or >11 years depending on the breed) is characterized by a prostatic hyperplasia. On the other hand, the decreased size of the gland, presumably due to a senile involution, is mainly influenced by the mean age of the dog: geriatric dogs of long life breeds (L2 mean age: 13 years) are more affected than geriatric dogs of short life breeds (S2 mean age: 10 years). It has to be further investigated whether geriatric dogs of breeds of long life expectancy have a predisposition to develop pathological conditions with potential negative effects on the prostate’s size such as testicular atrophy or endocrinopathies. References. 1) Adams et al., JSAP 2010;51:512-24. 2) O'Neill et al., Vet J 2013;198:638-43. 3) Siegal and Mordecai, Medicine Book of the Dogs 1995; Chapter 5. 4) Johnston et al., Anim Reprod Sci 2000;60-61:405-15. 5) O’Shea, J Comp Pathol 1962;72:321-31. 6) Gouletsou et al. Anim Reprod Sci, 2008;108:1-12. 7) Ruel et al., Vet Radiol Ultrasound 1998;39:212-6.