Growth and Calving Ease Birth, weaning, and yearling weights are normally used to evaluate breeding animals. Since environmental factors like feed and weather affect weights, actual or adjusted weight can be misleading if bulls come from different contemporary groups. Within a herd, weight ratios help account for some of the environmental differences between contemporary groups. A ratio of 100 means a bull's weight was average in his contemporary group. A ratio of 110 means a bull's weight was 10 percent heavier than average.
Ratios can also be misleading if bulls come from different herds.
EPDs, however, are calculated across herds. A bull's EPD for a trait is a more accurate estimate of his genetic worth than weight, adjusted weight, or ratio. EPDs not only account for contemporary group and herd differences they also include information on a bull's relatives as well as his individual performance. In all of these breeds, EPDs are expressed in pounds of calf. But, there are genetic correlations between birth, weaning yearling, and mature weight.