Sensitivity of female rabbits to changes in photoperiod as measured by pheromone emission.

Newborn rabbits are completely dependent on a pheromone on the mother's belly for the release of nipple-search behaviour and suckling. Using the stereotyped behavioural response of the pups as a bioassay it could be shown that: 1. In non-breeding does pheromone emission is stimulated by experimental long day and suppressed by experimental short day conditions within 1 to 2 weeks of reversing the light regime. 2. Under constant long day conditions pheromone emission, readiness to mate, conception rate and litter size remain high with no evidence of endogenous seasonal rhythmicity. 3. Experimental changes in daylength of just 1 or 2 h in either direction are sufficient to induce marked alterations in the level of pheromone emission, number of successful matings and average litter size within 2 to 3 weeks. Pheromone emission would thus seem to provide a sensitive test of photoperiodic responsiveness in non-breeding female rabbits, and a convenient, non-invasive indicator of their reproductive state.