ICBF have updated how expected calving dates are calculated so that farmers receive a more accurate guide to when animals are due to calve.
Accurate expected calving dates help Irish dairy and beef farmers plan labour, prepare calving pens, organise dry-off dates and monitor animals approaching calving. Until now, the calculation has relied mainly on the average gestation length of the sire breed. While useful, a breed average cannot capture the genetic differences between individual bulls and cows. New ICBF analysis shows that expected calving dates can be improved by using the gestation length, genetic merit of the sire and dam.
How the new expected calving date calculation works
Cattle have an average gestation length of about 283 days, but this can vary between breeds and between individual animals within the same breed. The previous method applied the sire’s breed average to all expected calves, whereas the updated approach uses the gestation-length Predicted Transmitting Ability (PTA) of both the sire and dam to adjust the 283-day base figure and calculate an expected calving date from the recorded serve date. A PTA estimates the genetic effect an animal is expected to pass on to its progeny, indicating whether a calf is more likely to be born earlier or later than the base figure. ICBF’s review found that this PTA-based method provided the best overall prediction accuracy.
Validation shows a clear improvement
Before implementing the change, validation work was completed to compare the existing breed-based method with the PTA-based calculation. The analysis used 482,376 calving records and measured how closely each predicted date matched the actual calving date. The Mean Absolute Error (MAE) is the average number of days between the predicted calving date and the actual calving date. A lower MAE indicates a more accurate prediction.
| Accuracy measure | Breed-only method | PTA method | Improvement |
| Mean Absolute Error | 10.79 days | 5.52 days | 5.27 days lower |
| Predicted within +/-1 day | 16% | 22% | +6% |
| Predicted within +/-3 days | 36% | 48% | +12% |
| Predicted within +/-7 days | 68% | 77% | +9% |
Further validation work was also done on a group of highly engaged herds with good quality data recording. Across these herds, the MAE decreased from 5.29 days using breed only predictions to 4.34 days using PTA predictions. This represents an average reduction of 0.95 days, or 18%. In addition, 86.5% of PTA predictions were within seven days of the actual birth date.
| Accuracy measure | Breed-only method | PTA method | Improvement |
| Mean Absolute Error | 5.29 | 4.34 | 0.95 days lower |
| Predicted within +/-1 day | 19% | 27% | +8% |
| Predicted within +/-3 days | 43% | 57% | +14% |
| Predicted within +/-7 days | 77% | 87% | +10% |
Overall, the validation results show a clear improvement from using PTA information. The validation analysis demonstrates that the PTA method provides a more accurate improvement in expected calving-date accuracy compared with the breed only approach.
What will this mean for farmers?
More accurate expected calving dates will help farmers make better-informed management decisions during the calving season. By providing a closer estimate of the actual calving date, farmers can more effectively monitor cows approaching calving, prepare calving facilities, and identify which animals should be moved into the calving pen, reducing the likelihood of cows calving unexpectedly.
How to get the best from your expected calving dates
The accuracy of expected calving dates depends on the quality of the breeding information recorded. Farmers can improve predictions by promptly recording all AI and stock bull serves, selecting the correct sire, keeping pregnancy diagnosis information up to date, and regularly checking the Expected Dairy Calving Profile or Expected Beef Calving Profile through their HerdPlus account.
A more useful prediction for the calving season
This update makes better use of ICBF genetic evaluations to provide expected calving dates that are tailored more closely to each mating. Validation shows that the PTA-based method predicts calving dates more accurately than the traditional breed-only approach, giving dairy and beef farmers more reliable and consistent information for planning and day-to-day herd management. Accurate and up-to-date serve, sire and pregnancy records remain essential to ensure farmers get the greatest benefit from the revised calculation across applicable ICBF systems.
Where to find your Expected Calving Dates
These improved expected calving dates are available to all HerdPlus herds through the Expected Dairy Calving Profile or Expected Beef Calving Profile in their HerdPlus Account. Farmers can also view the profile in the ICBF HerdPlus App, making it easy to check expected calving dates and support management decisions while on the go. The Expected calving report can also be downloaded printed for the milking parlour or calving shed, providing a useful reference point throughout the calving season. In addition, the expected calving dates will also be displayed on the dairy pocket notebook.