Sperm metabolism and duration of fertility were compared between roosters homozygous (RR) and heterozygous (Rr) for the rose comb allele. In the absence or presence of Ca+2, a motility agonist, the metabolic rate of spermatozoa from RR males was 76 to 77% of that of spermatozoa from Rr males. In the presence of caffeine, the metabolic rate of spermatozoa from RR males was increased significantly (P < .05) to 86% of that of spermatozoa from Rr males. Although intramagnal insemination of ejaculated spermatozoa reduced the disparity in duration of fertility between RR and Rr males, the duration of fertility of RR males was still less than that of Rr males. No difference in duration of fertility was observed following intramagnal insemination of testicular spermatozoa. Subfertility associated with RR males seems to stem from an aberrant activation or regulation of spermatozoal metabolism and not a reduction in absolute metabolic capacity per se.