Mouse reproductive fitness is maintained up to an ambient temperature of 28℃ when housed in individually-ventilated cages.

Production of genetically-modified mice is strongly dependent on environmental conditions. Mice are commonly housed at 22℃, which is significantly lower than their thermoneutral zone. But, when given a choice, mice often seem to prefer higher ambient temperatures. In the current study we investigated the effect of higher ambient temperature on the production of transgenic mice, with emphasis on embryo and sperm yield and quality. Mice (C57BL/6JOlaHsd) were housed under four different ambient temperatures (22, 25, 28 and 30℃). Female mice were superovulated, and mated with males. As indicators for reproductive fitness, the success of the mating was observed, including embryo yield and quality, as well as sperm count, motility and progressivity. Female mice were found to produce high amounts of high quality embryos from 22 to 28℃. Sperm count dropped continuously from 22 to 30℃, but sperm motility and progressivity remained high from 22 to 28℃. We conclude that mice can be housed at significantly higher temperatures than is commonly recommended without compromising embryo production and quality, or sperm quality. These results could lead to fundamental changes in how mouse facilities are built and operated - especially in warmer climates whereby energy consumption and therefore costs could be significantly reduced.