Likely the best way to evaluate and compare fertility potential of different males is to do a heterospermic trial.  Thus, semen containing equal number of motile sperm from two or more males is mixed in equal numbers.  These mixed samples are then inseminared into a number of females.  The percentage phenotype born shows the relative fertility potential. For example, if 100 cows are inseminated with mixed sperm from a black bull and a white bull and 80 black calves and 20 white calves are born, the black bull has a 4:1 advantage.

In the figure below, mixed semen from 9 bulls of different phenotypes were inseminated into cows.  Plotted is the known competitive index verses the %DFI and SD DFI (shown as αt here.  Note the very high correlations between competitive index and % DFI (r=74 (P < .05) and SD DFI (.94 (P< 0.01)/  Thus the higher the % DFI and SD DFI, the lower the bull fertility.  Note that %DFI values above ~ %DFI = 12% the fertility potential is serverly compromised.

The figure below shows % DFI from a single bull from mid life to aging - showing in agreement with the human data that aging is related to increased sperm DNA fragmentation.

The SCSA has proven its value in stallion breeding soundness exams.  The data below comes from Dr. Bob Kenny formerly at the Kennett Square center, the Univeristy of Pennsylvania.  Note for stallions also, the greater the increase in sperm DNA fragmentation, the lower the fertility index.  In a plenary session at a stallion reproduction session, Dr. Dixon Varner concluded his talk by saying : "If I had three measurements to evaluate stallion breeding soundness, I would choose, sperm concentration, sperm motility and SCSA testing."