The objective of this study was to investigate individual fixed effects in an animal model for breeding value estimation for semen traits of pig sire breeds. It was found the semen volume was greatest from October to December and least in March and April. Sperm concentrations were greater in winter and early spring and least in late summer and early autumn. Semen increased until about 2 years of age and remained relatively constant thereafter. Motility decreased steadily with age, wheras the percentage of abnormal sperm increased over the entire productive lifetime of the boar. Both total sperm number and number of functional sperm rose as the interval between collections increased to 10 days. It is concluded that AI centers should place economically optimal emphasis on boars with favorable estimated breeding values for semen traits.

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