Fall 2019

Barzona Bulletin A Publication of the Barzona Breeders Association of America Mature Cow Weight Considerations By David Lalman, Ph.D., Eric Devuyst, Ph.D., and Damona Doye, Ph.D., Oklahoma State University T he impact of mature cow weight on cow efficiency and ranch profitability in the United States has been discussed and debat- selected for more muscling over time while holding frame size in check. In fact, the genetic trend for ribeye area in most breeds of cattle indicates that the race for more muscle within each breed started in the 1980s and has accelerated in recent years.

According to the Livestock Marketing Information Center, cow carcass weights are increasing at a rate of about 3.75 pounds per year. Adjusted to a live-weight basis, this suggests that cow weights are increasing at an average rate of about 6.9 pounds per year. At the same time, Angus and Hereford breeders have been collecting mature cow weight data and calculating expected progeny differences (EPDs) for this trait for several years now. In both breeds, the genetic trend indicates a gradual increase in mature cow weight. These trends lead to an interesting question: If frame size is stable or gradually declining, what physical characteristics are changing that might explain the continued, albeit slow, climb in cow weights? The most logical answer is that beef cattle producers have

ed since the late 1800s. While there are many factors that influence the efficiency and profitability of cow-calf operations, cow size remains an important consid- eration. Aggressive selection for mature frame size occurred throughout the U.S. beef cattle industry during the 1960s, ‘70s and ‘80s. Around the late 1980s, frame size stabilized and then began to decline through the early 2000s. More moderate frame size, compared to that seen 30 years ago, is evident around the country. Nevertheless, indicators sug- gest that our nation’s beef cow herd con- tinues to increase in mature weight over time.

Selection for more rapid growth in cattle (higher weaning and yearling weights) began in the ‘70s and ‘80s and has continued ever since. With increased genetic capacity for growth combined with (until just recently) little to no selection pressure against feed intake, we have created a cattle population with greater appetite. Most feedyard consultants will tell you that cattle on feed today simply eat more feed for a longer period of time than they did 30 years ago. This is one reason carcass weights and finished cattle weights have increased so dramatically over the past 30 years. Generally speaking, along with greater appetite you get greater visceral organ mass. That is to say, cattle have larger organs, particularly liver, rumen and intestines, relative to their body weight than they used to have. This too could be part of the explanation for steady increases in mature cow weights. In an attempt to quantify the relationship of mature cow weight to calf weaning weight in commercial cow-calf operations, we evaluated 3,041 records collected from three different operations. In the data set, cow weights ranged from 635 to 1,922 pounds and calf weaning weight ranged from 270 to 775 pounds. First of all, there was not a strong relationship between cow size and calf weaning weight. In other words, there was a lot of variation in weaning weight, and cow size explained only a small Continued on page 4 ›

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