THE RATIONALE FOR CULLING OF RODENT LITTERS

Based on a review of the pertinent literature and our own unpublished data, it is recommended that culling of rodent litters in the early po stnatal period should be a standard practice in delivery-type reproduc tion studies. This, in turn, will reduce the litter size-induced varia bility in the growth and development of pups during the postnatal peri od and thus increase the sensitivity of statistical analyses to detect treatment-related effects. This will also ensure that any adverse eff ects on pup growth (body weight gain) and development (reflex and beha vior development) are not masked by a treatment-induced reduction in l itter size. The culling should be carried out randomly and no attempt should be made to selectively cull sick or underweight pups. Since mal e pups weigh significantly more than females and studies have shown di fferences in maternal behavior toward one sex over the other, whenever possible each culled litter should consist of an equal number of male s and females. (C) 1997 Society of Toxicology.