Cage ammonia levels during murine reproduction

Monogamous pairs of inbred BALB/c and outbred CD-1 mice housed in M2 cages with a floor area of 330 cm2, produced a mean cage ammonia level of 26 ppm and 154 ppm respectively over a four day period prior to weaning their litters. A gradient of ammonia exists from the nest to the food hopper. By housing CD-1 monogamous pairs in RM2 cages which have double the floor area of M2 cages (676 cm2), a lower mean level of ammonia was recorded at the same stage of reproduction and air sampling. The CD-1 mice in particular, were subjected to high levels of ammonia when compared with long term human health and safety occupational exposure limits of 25 ppm.