Summaryo The mating frequencies of 30 cockerels were studied under uniform conditions. These males belonged to 6 sire families and 15 fullsib pairs. It was found that there were significant differences between the sire families indicating that mating frequency has a genetic basis. When incompleted and completed matings were weighted, these genetic differences remained, and the use of a discriminatory analysis showed that the frequency of all types of mating was a satisfactory criterion of individual behaviour. During the course of mating frequency tests, monthly samples of semen were taken from the males. No correlation was found between the mating rank of a male and the quality of his semen assessed on volume, density and sperm morphology. The five top ranking and five lowest ranking males were tested for fertility and the top ranking males gave the best results as a group. A significant negative correlation (−0.4972) was found to exist between comb index (=height/width) and mating frequency. Furthermore, there was a correlation of −0.5055 between mating frequency and comb index calculated from the 15 dam-family averages of these variables and one of −0.6368 from the six sire family averages. Further analysis revealed the apparent absence of genetic variability in comb index, suggesting that the correlations were phenotypic only and indicating that the differences in mating activity could not be wholly explained on the basis of comb index. Finally, dubbing failed to improve the mating frequency of two low ranking cockerels to any great extent.
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