EN
The foxes cages from experimental group were blacked-out by tarpaulin for two consecutive months /from 1st August to 30th September/. In experimental and control groups were 3 undergroups: 1/ polish polar foxes, 2/ crosses with 50% genes of norwegian foxes /F₁/ and 3/ crosses with 25% genes of norwegian foxes /R₁/. The animals from every litter were allocated to both of group considering sex. The artificial abbreviation of daylight advantageously influenced on breeding's effectiveness of polish fox and crosses with norwegian fox. Economic effects showed profit 8.6% of crosses R₁ fur value as well as 21.7 % of polish foxes fur value and 20.4 % of crosses F₁ fur value.