What EPDs are and how to read them
By the RanchOS Global editorial team · Updated
In short: an EPD (expected progeny difference) predicts how much, on average, an animal’s offspring will differ from another animal’s offspring of the same breed. It compares bulls and cows as parents; it does not judge the animal itself.
How to read an EPD
EPDs are compared between animals. If bull A has a weaning weight EPD of +60 lb and bull B +40 lb, bull A’s calves are expected to average 20 lb heavier at weaning than bull B’s, when both are bred to similar cows under the same conditions. A single number says little on its own; the difference between two animals does.
An EPD is half of the animal’s breeding value, because each parent passes on half of its genes.
The most common EPDs
| EPD | A higher value means | Unit |
|---|---|---|
| Calving ease direct (CED) | Easier calving in first-calf heifers | % |
| Birth weight (BW) | Heavier calves at birth | lb |
| Weaning weight (WW) | Heavier calves at weaning | lb |
| Yearling weight (YW) | Heavier calves at about one year | lb |
| Maternal milk (MM) | More weaning weight from milk in daughters’ calves | lb |
| Stayability (STAY) | Daughters more likely to stay productive | % |
| Docility (DOC) | Calmer yearlings | % |
| Marbling (MARB) | More marbling in the carcass | score |
For birth weight, breeders usually look for a lower value to protect calving.
Accuracy: how much to trust an EPD
Accuracy (ACC) runs from 0 to 1. Near 0, the EPD is uncertain and can move a lot; near 1, many calves and records back it up. Example: two bulls with a birth weight EPD of 1.2. The young bull, at 0.1 accuracy, could change by ±2.7 lb; the proven bull, at 0.8 accuracy, by only ±0.6 lb. Genomic information raises the accuracy of young animals.
Percentile ranks
A percentile rank compares an animal with its whole breed. Lower is better: a bull in the 30% percentile for weaning weight is in the top 30% of the breed.
Three rules
- Compare EPDs only within the same breed and evaluation; across breeds, use adjustment factors.
- Use current values: breed averages shift every year.
- Choose for your goal. No bull is best at everything.
To find bulls by breed, browse the ranch directory or read How to buy registered bull semen.