Herd fertility
Pregnancy rate and calving interval calculator
Four counts from your records show where the calves go missing between turnout and weaning.
Pregnancy rate = cows pregnant ÷ cows exposed. Calving rate = calves born ÷ cows exposed. Weaning rate = calves weaned ÷ cows exposed. Calving interval = days open + 283 days of gestation. With 100 cows exposed, 92 pregnant, 89 calves born and 86 weaned, the rates are 92%, 89% and 86%. With 85 days open, the calving interval is 368 days.
Example numbers. Change them to your own.
Reading the numbers
- Always divide by cows exposed. Dividing by cows that calved hides the open cows, and they cost a full year of upkeep too.
- Look at the gaps. Pregnancy rate minus calving rate is loss during pregnancy. Calving rate minus weaning rate is calves lost between birth and weaning.
- Days open drive the interval. Gestation averages about 283 days (Beef Improvement Federation), so a cow has to settle within about 82 days of calving to calve every 365 days.
- Compare with your own past years. The same counts taken the same way each year show whether a change in bulls, nutrition or the breeding season worked.
How do you calculate pregnancy rate in beef cattle?
Divide the number of cows found pregnant by the number of cows exposed to the bull or AI, and multiply by 100. 92 pregnant out of 100 exposed is a 92% pregnancy rate.
What is calving interval and how is it calculated?
Calving interval is the time between two calvings of the same cow. It equals the days from calving to conception (days open) plus gestation, about 283 days. 85 days open gives a 368-day interval.
What is the difference between calving rate and weaning rate?
Calving rate counts calves born per cow exposed. Weaning rate counts calves weaned per cow exposed, so it also includes calves lost between birth and weaning. Weaning rate is the one that decides how many calves you sell.