Restricting the mating period to 9 weeks is a recommendation to Stabiliser breeders so that they can reap the benefits of a tight calving pattern. Data from the 2016 calving season for over 1000 cows shows the kind of pattern of births that can be reasonably expected.
Because gestation length is a little variable a 9 week bulling period is typically going give a 10 week calving period. The data here shows that 55% of births occur in the first 3 weeks of the calving season and 74% in the first 4 weeks. 98% of births have happened by the end of week 8. Typical barren rate for this pattern is 4%.
The benefits to the herd are a focus on calving management – which improves survival, reduced disease risk to calves – because they have a similar age and a higher average weaning weight – because calves will have an older average age come weaning time.
Is 9 weeks too long?
Given the high fertility exhibited by Stabiliser cows could the bulling period be shorten further? What would be the consequences for costs and income?
Based on this data set if we had only kept the bulls in for 7 weeks then we might reasonably expect the calving to occur over 8 weeks. This would mean 2.3 fewer calves per 100 cows and 2.3 more barren cows. That change would mean a reduced income of £1040 per 100 cows from 2.3 of the smallest calves not available to sell (or value) at weaning. Replacement rates would remain the same it would just alter the ratio between voluntary and involuntary culls.
So the question comes down to, “Is there £1040 of labour and other savings (per 100 cows) to be had by bulling for 7 weeks rather than 9?”