In most breeds of domestic animals, recessive lethal genes are known. For example, in the Yorkshire breed of cows

In most breeds of domestic animals, recessive lethal genes are known. For example, in the Yorkshire breed of cows, a gene that causes dropsy is widespread, which leads to the death of calves at birth. Why are such lethal genes often found in one herd or nursery?

Often found, because inbreeding is used in pets, that is, closely related mating, one prominent producer has recessive lethal genes that are transmitted to all its offspring.