Double-decker cage reduces mount frequency and ejaculation latency, resulting in reduced weight loss in male rats...

Rats were the first mammals to be domesticated for scientific research, and abundant physiological data are available on them. Rats are expected to continue to play an important role as experimental animals, especially with advancements such as CRISPR/Cas9 technology. Environmental enrichment aims to promote species-specific behaviors and psychological well-being. In the present study, we designed a double-decker (DD) cage, which utilizes two stacked plastic cages for rat enrichment, and investigated the influence of housing in the DD cage on rat mating behavior. The results indicated that mount frequency, total mount counts, and total ejaculation latency were significantly lower in the DD cages than in the single-decker (SD) cages. Notably, in the DD cages, the body weight loss of male rats after mating behavior was lower than that observed in the SD cage. Water consumption per day during mating behavior was also significantly lower in the DD cages, although no significant differences were observed in daily food intake during mating behavior. In addition, reproductive performance, including pregnancy rate and birth rate, did not change in the DD cages. In summary, our study demonstrated that DD cages reduce mount frequency and ejaculation latency during rat mating, resulting in decreased water consumption and weight loss in male rats. Therefore, housing in DD cages may serve as a beneficial enrichment for rats.