Why We're Paying Less Attention to EPD's
Why We’re Paying Less Attention to EPD’s
Expected Progeny Differences (EPD’s) are the numbers calculated by breed associations based upon data received from registered breeders. The purpose of the numbers is to compare the performance of cattle across a breed.
Original EPD measurements in the Hereford breed were for birth weight (BW), weaning weight (WW), Yearling Weight (YW), Maternal Milk (MM), and Scrotal Circumference (SC). It appears that EPD’s became a factor affecting genetic selection in the 1970’s. The original Hereford EPD’s have 1977 as the base year.
More recently, EPD’s have been created for Rib Eye Area (REA), Intramuscular Fat (IMF), and Back Fat (BF).
Presently, most Hereford breeders focus on growth characteristics such as weaning weight, yearling weight, and maternal milk.
Many Hereford breeders have embraced EPD’s as performance data, and they manage their herds to maximize total performance among EPD’s. There is no Hereford EPD for mature size or for weaning weight relative to mature size. Because EPD’s do not take into account animal size, the top total performing sires and dams tend to be larger. I have found that there is a tremendous positive correlation between parental mature size and yearling weights (once accurately calculated).
I have purchased more than 100 registered Hereford cows from more than 20 separate breeders in the past six years. I have turned the cows out on my fescue/orchardgrass/clover fields in Central Virginia, and managed them as lightly as possible.
The variance in performance is astounding, and it has practically little correlation to EPD’s. Specifically, the M&G numbers (a calculated EPD that equals the Maternal Milk EPD plus ½ of the Weaning Weight EPD) for my herd range from 21 to 53. The M&G number is supposed to calculate the expected variance in calf weaning weights, all other factors (sire, environment, dam age, etc) being equal. My best cow has a M&G number of 28. This cow is only a three year old, so there is not a lot of data for her yet. My best proven cow has a M&G score of 36. This cow, DTF Kaleigh 15G 917, is a 1999 cow that has had the best performing spring calf in my field by more than 20 pounds on average for the last four years. Further, this cow weighs about 1350 pounds, 200-400 pounds less than some of the cows that she competes against.
At the opposite end of the spectrum is VPI Miss Promise K016, a heifer that I bought from Virginia Tech at a sale in 2001. I had to calves by this cow, one to VPI Limited Edition J921, and one to KCF Bennett 774 L153. Both of the calves were by far the worst performing among their contemporaries. Further, once removed from the dam, they still did not grow well. Additionally, the dam’s hooves grew too long and were problematic, and she did very poorly when the only forage available was low-quality stock-piled fescue. When I culled her, she weighed 1550 pounds (she was not yet fully mature). Her current M&G EPD is 33, better than my best cow, and practically the same as my best proven cow.
Over time, EPD’s do move to reflect the performance of an animal, but the numbers move too slowly and in an erratic fashion. Because of the lack of accuracy of EPD’s and because of their stagnation, it is quite easy to manipulate EPD’s. For example, I’ve had the thought of taking my best cows, and breeding them to a very growthy bull with low EPD’s. At the same time, I will take some of my worst cows with very high M&G EPD’s and breed them to a top M&G bull like KCF Bennett 3008 M326. I am very confident that my good cows bred to the low numbers bull would dramatically outperform my high EPD bad cows bred to M326. Given relative accuracies, I believe my high EPD cows would see their numbers drop dramatically, whereas my good performing cows would only see a minor increase in EPD’s.
Within a stable herd, growth EPD’s really do denote relative growth among bloodlines over a period of 5-10 years. Of the cows that I bought in 2000, the cow that produced the highest growth calf, ARW DR X4 LASS 334, now has the highest M&G of the group, 45.The worst of the group, ARW ANTO VIC 232, has a M&G of 31. The top performing cow, however, had a mature weight of approximately 1800 pounds.
By chasing growth EPD’s and not focusing on efficiency, Hereford breeders are creating large cattle. My experience is that dams reach mature weight at approximately five years. I have sold mature Hereford cattle bought from well-known, reputable Hereford breeders, that weighed in excess of 1800 pounds. I sold one cow that exceeded 2000 pounds. I am confident that Hereford cows exist that can consistently wean calves at more than 600 pounds, up from about 450 pounds 30 years ago. I believe the current cows, however, exceed 1500 pounds at maturity whereas than cows 30 years ago likely were at least 300 pounds lighter. From an efficiency standpoint, a 450 pound calf from a 1200 pound dam equals a 600 pound calf from a 1500 pound dam.