One important attribute of a beef-breeding cow is the
ability to wean a calf every year. Furthermore, an earlierborn
calf is likely to be heavier at weaning and its dam has
more opportunity to conceive again during the following
breeding season. In a spring-calving system under the
seasonal pastoral-grazing system in New Zealand, a 365-
day intercalving interval is desirable. A normal gestation
length is 280 days leaving 85 days for a cow to resume
oestrous cycles and conceive again to maintain the 365-
day calving interval. Literature estimates of the interval
between calving and the first oestrous cycle post-calving
are 53-82 days for mixed-aged beef-breeding cows and
81-95 days for first-lactation beef-breeding cows (Hickson
et al. 2012; Knight & Nicoll 1978; Morris et al. 1978;
Smeaton et al. 1986), indicating that a 365-day calving
interval is difficult to maintain.
An alternative reproductive performance measure to
intercalving interval, and favoured in naturally mated beefcow
herds, is days to calving, that is defined as the number
of days from the start of joining to the day of calving. Days
to calving has become the standard fertility trait for genetic
evaluation (Meyer et al. 1990; 1991; Johnston & Bunter
1996).
A study was conducted to investigate the effects of
breed group, year of calving and conception cycle on
intercalving intervals and days to calving in straight-bred
Angus and Angus-cross-Friesian, Angus-cross-Jersey and
Angus-cross-Kiwicross cows from first mating as heifers
through to their sixth calving.
