Keep ’er one more year. 

This is the punch line of one of the funniest poems ever penned by humorist Baxter Black. The poem describes the agonizing decision of a sentimental rancher over whether to cull an old cow. He remembers her as a maiden. He remembers her as a matron. Now, he sees her as a senior  —   sharp in the hips, lean in the ribs, smooth in the mouth and long in the jaw. She ought to go to town, but  …

I guarantee you would laugh heartily when hearing Baxter recite this old-cow poem. But it’s no laughing matter in real life when you’re wrong about when to own a cow.

As with many other things in life, it is wise in cow ownership to read the instructions before all else fails. And one of the best sources for doing this is a publication of the Beef Improvement Federation titled Guidelines for Uniform Beef Improvement Programs, Seventh Edition (users of this reference simply call it BIF Guidelines). This reference contains numerous age-of-dam adjustment tables that put cow culling into a very meaningful perspective. Another excellent reference is a summary paper published in February 2004, Genetics and Molecular Research. The authors are animal scientists Janice M. Rumph of Montana State University and L. Dale Van Vleck of the U.S. Meat Animal Research Center in Nebraska.

The paper by Drs. Rumph and Van Vleck summarizes the surprising amount of research that has gone into relationships between the age of cows and the birth and weaning weights of calves. Contained in the paper are 30 references dating to the 1950s. Fifty-seven percent of the papers were published in the 1970s and 1980s, and papers were still being published in 2002. Drs. Rumph and Van Vleck concluded that adjustment factors are necessary for accurate national genetic evaluations. 

They also concluded that adjustment factors are indeed required for both birth weight and weaning weight. However, they concluded that separate birth-weight adjustments were not required for male and female progeny but were required for weaning weights. And, while the Beef Improvement Federation offers a one-size-fits-all adjustment chart (see accompanying Standard Adjustment Factors), other charts show factors that vary by breeds.

BIF’s standard chart shows that if the mythical cow in Baxter’s poem were 11 years of age or older, she should have gone to town. On the average, prime-time cows are 5 to 10 years old. They give you six calves with weaning weights as good as they can be. But the research shows that while the prime-time, adjustment-free period can be six years in one breed, it can be only two years in another.

In a perfect world, you would own only prime-time cows. These cows are in the prime of their productive lives because of their ability to provide the necessary uterine environment and nutrients for fetal development and pre-weaning growth. As is shown in the accompanying table, heifers up to 4 years of age and cows above 10 years of age wean lighter calves than prime-time cows. The value of these weight differences can be substantial. For example, if, as shown in the table, a male calf out of a first-calf heifer actually weaned 60 pounds lighter than one out of a mature cow, that monetary difference would have been worth $65 on last fall’s market. 

But, the cattle industry would rapidly run out of cows if everyone owned only cows that were 5 to 10 years old. That’s why the productivity losses inherent in heifer development are an essential part of beef production. This argument, however, does not support the keep ’er one more year decision of Baxter Black’s cowman if that cow were 11 years of age or older. You can suffer unnecessary hurt by laughing at that reality.

To contact Fred Knop, write Drovers or send e-mail to