Efficiency, reproduction and the cow-size dilemma

We often hear that smaller cows can improve production efficiency, especially in areas of low rainfall and sparse forage. At the same time, we know that smaller cows tend to produce smaller steers, potentially meaning lighter pay weights for weaned calves or finished cattle.
Experts from across the industry discussed the relationships and tradeoffs between cow size and feed efficiency, reproduction and profitability during a seminar last Friday prior to the Leachman Cattle of Colorado bull sale.
Colorado State University animal scientist Milt Thomas, PhD., led off with a discussion of cow size and fertility in an arid environment. He outlined results of a long-term research project with Brangus cattle in Mexico’s Chihuahuan Desert. Through the 1970s and 1980s, cow weights in the study herds tended to grow heavier, and at the same time, pregnancy rates dropped off. During the 1990s, managers began focusing more of their selection on fertility, and as they did so, cow weights, on average, became lighter. Calf weaning weights meanwhile, remained about the same. Weaning weights, he says, fluctuate year-to-year within herds based on environmental factors, but the general genetic trend is toward heavier weaning weights.
Thomas says the idea that lighter cows would be better adapted to a desert environment is not surprising, and notes the same concept applies to semi-arid areas as well. But besides cow mature weights, he says the growth curve is in young females is an important factor in fertility. Selection pressure for fertility tends to favor a steeper growth curve, meaning heifers have faster early growth and reach mature weights earlier in life. This trend toward early maturity appears to coincide with better fertility in young cows, meaning heifers conceive early in the breeding season and have better re-breeding success.
John Maddux, of Maddux Cattle Company in Nebraska, outlined how cow size matters on his family’s operation. Noting that the optimum cow size for any ranch depends on the production environment, marketing goals and other factors, he says smaller cows have fit his family’s system. In 2005, the Maddux family dispersed their entire cow herd, then rebuilt it to capitalize on what they saw as a new reality – higher grain prices.
The family shifted their calving season later, in April and May, and changed to a cow-calf and yearling system. Their goal is to market nine-weight long yearlings in August, a time when demand for that class of cattle is high. For managing and marketing 16-month-old yearlings, he says, high growth potential is not necessary, and could be detrimental, with the calves growing too heavy for feedyard buyers.
Also, the family wants a self-sufficient cow herd. Their cows graze native range through the summer and corn stalks from November through March, with virtually no hay or supplements. First-calf heifers receive some protein cake, but supplementation is minimal. So, Maddux says, fertility is twice as important as growth traits in their herd.
Toward that goal, they developed their own maternal-composite breeding system, targeting three-eights Red Angus and one-quarter Terentaise, with the remaining genetic makeup split evenly between Red Poll, South Devon and Devon. The family chose this breed makeup, and uses individual selection for moderate size and high-fertility cows in a low-input production system. Cow mature weights average about 1,150 to 1,200 pounds.
Maddux acknowledges that growth potential remains important for the value of calves in later production stages. He stresses though, that selection based too much on growth can have negative impacts in terms of maintenance requirements and fertility in cows. Echoing what Thomas said earlier, Maddux says it is fairly easy to select for growth overall. Selecting for early growth, which benefits fertility, is more complex, but can be achieved without pushing cow mature weights too high.
Later this week, part two of this series will cover the cattle feeder’s perspective and other discussion on cow size, efficiency and reproduction from the Leachman seminar.



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