The effects of four seasons of semen collection and of artificial insemination on conception
in dairy cows were studied. The solstices and equinoxes (December, March, June and
September) defined the beginning and/or end of each season. Semen was collected from
973 progeny-test bulls over 8 years at the two Norwegian AI stations at 60.8° N and 63.4° N
where artificial light was used to provide a minimum photoperiod of 10h/day. The effect of
using semen of elite bulls during progeny testing and after selection as elite sires also was …