Suckling behaviour and fertility in beef cows on pasture.
The suckling behaviour of 66 Hereford and Simmentaler cows was studied. The average frequency of suckling in 24 hours was four times, and the average duration of each suckling bout was 10 minutes. Suckling events were not evenly distributed throughout the 24 hour period. Regardless of suckling frequency or days post partum, the most favoured suckling period was between 04:00 and 06:00, i.e. dawn. The lowest incidence of suckling was recorded in the period from midnight to dawn. The longest interval between two suckling bouts over the 24 hours always occurred before the dawn and became longer as the calf grew older (p<0,01). Once the mating season commenced, the onset of oestrus was positively correlated (p<0,01) to the length of the longest inter-suckling period. Suckling behaviour was not affected by the milk yields of the cows studied . In a follow up investigation, 88 cows were separated from their calves for 12 hours out of 24, for the fortnight prior to the start of the breeding season. Fifty-six percent of the 44 cows which were separated from their calves from 18:00 to 06:00 (dayfeeders) exhibited oestrus within 28 days of the breeding season, compared to 22% of the group separated from 06:00 to 18:00 (p<0,01). It was concluded that not only the suppression of suckling may be involved in the onset of ovarian activity . The specific time period during the 24 hours when suckling is prohibited may also play a role.