ABSTRACT
Linebreeding builds up homozygosity and prepotency within a breed because it is a form of inbreeding. The homozygosity produced by linebreeding is generally for increased merit for desired traits because it is a slower form of inbreeding and usually is carried on in conjunction with a rather strict selection and culling program. Linebreeding is best accomplished by breeders whose herds are superior to the average of the breed. Outcrossing is a minor part, but eventually a necessary part, of most linebreeding programs. Any inbreeding program that is carried far enough will probably fix some undesirable traits, and mild outcrossing will be needed to remedy the undesirable traits. Linebreeding has a definite place for the serious horse breeder, regardless of the breed or traits being selected for. Cutters and reiners practice linebreeding more vigorously than do breeders of racehorses primarily because of the heritability of the traits.
