How to Test Mating

Test-mating is a system employed to determine whether an animal—usually a buck—carries one or more particular and undesirable characteristics, that is to say whether the animal is heterozygous for certain undesirable recessive genes.
There are two methods of test-mating. In the first method the animal to be tested is mated to another which is homozygous for the character. For example, a breeder may wish to test whether a buck carries the factor for long hair or woolliness.He will thus mate the buck to an Angora doe. If the buck is heterozygous for woolly, then approximately half of the progeny will be woolly, but if the buck does not carry the gene for woolliness, as short hair is dominant to long hair, all the progeny will be short haired. In the same way, to test whether an Havana carries the dilution factor, the rabbit would be mated to a lilac, which is of course the homozygous dilute brown. If no lilacs are produced, then the Havana does not carry the dilute factor.

Certain undesirable recessives are lethal or semi-lethal when present in the homozygous form. In this case the rabbit must he tested with a known heterozygous for the factor, selects approximately one quarter of the progeny will be homozygous for the recessive character if the buck carries it.

The second method of test-mating is by breeding back his daughters to the buck in question. If the buck is heterozygous for any gene, obviously approximately one half of his daughter swill be homozygous or heterozygous for that character, depend-in on the constitution of their dam. Therefore a mating between the buck and his daughters will always yield at lea stone quarter of the progeny as recessive homo zygotes in approximately half the litters. If then a buck is mated with say six of his daughters, and in all their litters, say thirty young,none is homozygous for the undesirable character, then the buck can safely be considered to be free from that recessive.The second method of test-mating is more laborious than the first, but it has the advantage that not only does it test the buck for one particular gene, but it tests for all others at the same time. Any undesirable recessive genes in the buck's constitution will be shown up.
In both systems, enough young must be produced before the test can be considered reliable. In the first method two litters from does showing the recessive character to be tested would be sufficient. In the second system at least six daughters, and preferably more, should be mated back to the buck.

Test mating a stud buck will quickly remove any unwanted recessive characters, even though the does are not tested, for the use of a buck which is definitely clear of the recessive gene will reduce the proportion of heterozygous in a stud by 5o%in each generation.

Test-mating should not be confused with progeny testing,which is of course the estimation of the breeding worth of abu ck (or doe) on the basis of the value of his (or her) progeny.