This is a guest post written by Karin Schmid, Beef Production Specialist with the Alberta Beef Producers.
Bull buying season is upon us. If your house is anything like my family’s, most available surfaces are now piled high with catalogues advertising the next great herdsire. There are many factors that play a role in choosing a new bull for your operation (visual observation, breed, pedigree, actual birth weight, residual feed intake (RFI), weaning weights, breeding soundness evaluation, etc.), but one tool that can aid in herdsire selection has led to a lot of confusion since its first use over 40 years ago. Let’s decipher this valuable tool so you can expertly evaluate potential herdsires as you flip through those sale catalogues.
Expected Progeny Differencess defined
Expected Progeny Differences (EPDs) are estimates of an animal’s genetic merit as a parent. EPDs are the difference between the predicted average performance of an animal’s future progeny and the average progeny performance of another animal whose EPD is zero, assuming that the bulls are mated to similar cows, or vice versa. For example, if Bull A has a birthweight EPD of +9.0 lbs and Bull B has a birthweight EPD of +3.0 lbs, this means that Bull A’s calves will have birthweights that are 6 lbs heavier than whatever the birthweight of Bull B’s calves are, on average.
To compensate for differences in environment and management, contemporary groupings are used. Contemporary groups are animals of the same age and sex raised under the same management conditions. Once these factors are accounted for, the genetic component is the part that remains, and that is what EPDs predict. Information used in computing EPDs includes pedigree and performance of the individual animal, all relatives, and progeny. It is often assumed that EPDs are calculated in much the same way as 205 day adjusted weights, but this is not the case. To correctly calculate EPDs, millions of equations must be solved simultaneously.
Many different EPDs exist, from calving ease and weaning weight, to ribeye area and marbling, to cow weight and stayability. EPDs are generally reported in the same units as the traits they measure (pounds for weight traits, square inches for ribeye, etc.).
Continue reading the rest of the article and more about EPD’s at Beef Cattle Research Council
Link Photo courtesy of Chema Concellon
Do you use EPD’s in selecting bulls for your herd? What other information is important to you when selecting your herd sires?