Eight adult rams were housed in 16L[light]:8D [dark] for 16 wk and then exposed to short days (8L:16D) or skeleton short days (11L:1D:5L:7D) for 16 wk before being returned to long days. The skeleton treatment promoted testicular development and regression in a way similar to that occurring in 8L:16D, indicating that a change in the total quantity of light is not a prerequisite for the photoperiodic response in the ram.