Testis development and daily sperm output in guineas submitted to progressively increasing daily photoperiods at...

Four hundred and eighty guineas were raised under short days (7L:17D) from 3 weeks of age, then subjected to increasing light at 8, 16, 20, or 24 weeks of age. After receiving 7 additional hours of light (+ 1 hr per week) for each of 7 consecutive weeks, each group was then maintained on long days (14L:10D) until 70 weeks of age. No significant differences were observed between photoschedules for growth rate or adult body weight; however, the age at which the daylengths were increased greatly influenced the development of the testes and daily sperm output (DSO). The earlier the age birds were submitted to increasing light, the sooner the rapid phase of testis growth occurred and the lower adult testicular weight. Results were similar in the mean DSO expressed as a function of the age or photoschedule. Male guineas preconditioned by short days and submitted to increasing daylength from 20 weeks of age appeared to reach sperm production sufficiently early to inseminate contemporary females as they started to lay. Sperm production was high enough to ensure insemination of 6 to 12 females per male instead of the usual 3 to 4 under the present management conditions in the industry.