Animals with parity 0, 1, 2, and ≥ 3 were managed in separate groups, assigned at
the start of each yearly breeding season. Parity groups were managed in the same facility
and inseminated by the same technician each year. The breeding season for heifers started on 15 October every year and consisted of 50 days of continuous visual oestrus
observation, with once daily artificial insemination (AI) at 09h00. The breeding season
for cows started on 1 November and consisted of 60 days of oestrus observation and AI
in a similar way. Inter-oestrus periods of nulliparous heifers ranged from 16 to 24 days
(mean 20 days). Days to first oestrus was defined as either the days to first insemination
if it resulted in a pregnancy, or the days to the first insemination that was followed by a
normal (16 to 24 days) inter-oestrus interval, or if neither of the above occurred it was the
days to the last insemination.