Influence of inbreeding on reproductive performance, ejaculate quality and testicular volume in the dog.

An established foxhound colony employing an outbreeding and inbreeding program was evaluated to assess the influence of increased homozygosity on overall reproductive performance and ejaculate quality. A total of 14 outbred and four inbred male dogs were naturally bred to 544 outbred and 51 inbred bitches, respectively. Mean conception rate and total number of puppies whelped and number born alive were greater (P<0.01) in outbred compared to inbred lines. Duration of gestation and number of puppies surviving from birth to weaning were not different between outbred and inbred groups. Ejaculate quality of studs also appeared affected by genotype with outbred males producing a greater (P<0.025) average sperm count/ejaculate and sperm count/ml of ejaculate. Ejaculate volume, % motility of spermatozoa and testes volume, although not significantly different, also favored the outbred compared to inbred sires. These results: 1) indicate that a breeding program utilizing dogs with inbreeding coefficients ranging from .125-.558 can experience reduced reproductive performance; 2) suggest that a portion of the infertility associated with conception may be attributed to the male, since inbred studs produced lower quality ejaculates compared to outbred counterparts.