The aim of the study was to determine the effects of age and breed of chinchillas on the litter size, number of weaned chinchillas per litter, length of whelping interval, and nursing mortality of young chinchillas. The analysis involved 2576 litters from 790 standard chinchilla females of two genetic groups, 585 Polish and 205 Danish females. The Polish chinchillas achieved slightly better reproduction performance, because the litter size as well as the number of weaned per litter and nursing mortality were higher than those of the Danish chinchillas. Almost all the analyzed parameters (apart from whelping interval) increased until five years of age, thereafter decreased, and again increased – reaching a good level in the older group of chinchillas. It seems also that longer management of the breeding stock than five years would be purposeful.

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