Since the early 1980s I have been trying to get people to understand that the “problem” with practical fertility (as opposed to academic fertility) is that we force cows to calve out of sync with the environment. The result is that we try and rectify the symptom of low reconception by extending the breeding season from anywhere between 2 months and 12 months.
Body condition at calving is the most important determinant of cow fertility.
Body condition is determined by genetics (inherent body condition) and nutrition. The graph below shows the seasonal influence on nutrition / body condition / fertility. Bear in mind that the results shown are from a seasonal rainfall area where the rains normally start mid-November and end mid-March.
Looking at the above graph:
- The difference in interval between calving and first heat (PPAP) from 135 days (September) to 40 days (January) is solely due to naturally occurring nutrition (dry / green grass).
- The importance of genotype. With a fatter genotype, in this environment, the figures on the graph could change to something like 100 days in September to 40 in mid-November – that is the influence genetics.
By breeding mid-March for calving beginning January one only requires a 42 day (2 heat cycles) breeding season for high practical fertility. Such a timetable also coincides with maximum yearling heifer fertility.
The advantages of a 42 day breeding season are:
- Higher practical fertility / profitability.
- Effective supplementation.
- Effective Selection.
- Easier management.
- Effective AI. I have achieved 60% calves born within 2 weeks via partial synchronization and AI.
Combine the above with a strategy of 4 month weaning and we have solved most of the current cow fertility problems.