The on-Going, Unfolding Story of Sperm Mobility

A genotype x environment interaction was explored by feeding cockerels 6-N-propyl-2-thioruacil (PTU; see Kirby et al., 1996).  These cockerels were from a line of chickens selected for high sperm mobility.  The experiment was based upon the following argument:  if sperm mobility is affected by PTU-mediated testis hypertrophy, then phenotype is affected by testis size.  Cockerels at six weeks of age (n = 60 per treatment group) were assigned randomly to one of two treatments:  (1) a control diet, or (2) 0.1% (w/w) PTU for 6 wk.  Sperm mobility phenotype was measured at 27 weeks of age.  Data were analyzed by ANOVA.  A treatment effect was not observed (P > 0.05).  Percentages of mobile sperm were 57 + 13.9 and 55 + 15.3% (mean + SD) for control and PTU-treated roosters, respectively.  Combined testis weight was measured from a random sample of roosters (n = 20 per treatment group) after body weight was recorded.  PTU treatment decreased both body weight and combined testis weight (P < 0.01).  In contrast, testis weight expressed as a percentage of body weight did not differ between control and PTU-treated roosters (P > 0.05).  In summary, whereas PTU treatment did not increase testis weight as expected, PTU treatment nonetheless affected body growth and testis development.  However, sperm mobility phenotype was not affected.  In conclusion, if disruption of neuroendocrine mechanisms underlying growth and sexual maturation had no effect upon sperm mobility phenotype, then the extent to which environmental factors affect phenotype must be questioned.