They are necessary for health, maintenance, growth, egg production and hatchability. Vitamins of vitamin-forming substances are complex, organic compounds consisting of various combinations and proportions of carbon, hydrogen, oxygen and nitrogen, and possibly other elements. This has led to a complete reorganization of the poultry industry, based on the earlier hatching of chicks and the year around confinement of laying hens. The discovery of vitamins has been of practical importance to poultry keepers, as it is now possible to rear chicks at any time of the year regardless of climatic conditions and to keep laying hens in strict confinement without apparent loss of health and vitality. Vitamins play a very important part in poultry nutrition. During the winter, their diet overlaps more with that of the polecat, and they will eat a larger proportion of rodents than in the summer, although they still rely heavily on frogs and rarely scavenge for food from ungulate carcasses as the polecat does. During the summer period, the diet of wild polecat-mink hybrids is more similar to that of the mink than to the polecat, as they feed predominantly on frogs. Studies on the behavioral ecology of free ranging polecat-mink hybrids in the upper reaches of the Lovat River indicate that hybrids will stray from aquatic habitats more readily than pure minks, and will tolerate both parent species entering their territories. Originally bred for their fur (which was more valuable than that of either parent species), the breeding of these hybrids declined as European mink populations decreased. The first captive polecat-mink hybrid was created in 1978 by Soviet zoologist Dr. They are very difficult to tame and breed, as males are sterile, though females are fertile. Hybrids can swim well like minks and burrow for food like polecats. The majority of polecat-mink hybrids have skulls bearing greater similarities to those of polecats than to minks.

They are fairly large, with males attaining the peak sizes known for European polecats (weighing 1,120-1,746 g and measuring 41-47 cm in length) and females being much larger than female European minks (weighing 742 g and measuring 37 cm in length). Polecat-mink hybrids have a poorly defined facial mask have yellow fur on the ears, grey-yellow underfur and long, dark brown guard hairs. The two species likely began hybridizing during the early 20th century, when northern Europe underwent a warm climatic period which coincided with an expansion of the range of the polecat into the mink's habitat. Such hybridization is very rare in the wild, and typically only occurs where European mink are declining. A Polecat-Mink Hybrid, also known as khonorik by fanciers, is a hybrid between a European polecat and a European mink.

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