The purpose of the studies was an attempt to evaluate influence of females’ whelping date on reproduction traits as well as establish factors, which can exert an influence on that trait. The material for the study was represented by data obtained from breeding documentation of a fur-animal breeding farm of standard minks. Twelve generations of animals were taken into consideration. Whelping date informations came from 10 611 litters. Influence of the factors determinated the level of examination reproduction traits were were performed by many-factor analysis of variance by the Low Square Method using procedure of a statistical package SAS [1996]. The factor, which in the highly significant determinated litter size and weaned cubs was female’s whelping date. The highest litter size were from females, which the whealping date was between 111-115 day of a year (4.87 cubs). Noticeable litter size reduced was observed when the whelping date was after 30ty April (from 120 day of a year). The overrunning whelping date also decreased probability of get cubs. The most profitable values of reproduction traits were observed at females, which whelping date was between 111 and 119 day of a year. In the research showed the highly significant determination of the heat ending time, the number of days from the begining to the end of heatting, the age of females and a year of whelping exert an influence on whelping date. When the end of the heat was in the first days of March (from 3rd to 7th) then whelping date was between 114 and 115 day of a year, and then was shifted on the next days of a year. Possibility of the whelping date between 111 and 115 day of a year (guarantee higher litter size) was the highest in the groups of two and three years old females, simultaneously in that classes decreased probability of delivery in periods unfavourably affect on females’ litter size (from 120 to 134 day of a year).

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