by: Wes Ishmael

It can be downright disheartening to discover that what used to be correct, what you took for granted as still correct, is in fact dead wrong. Such realizations can pay dividends, though.

Consider mature cow weight. Depending on the part of the country, lots of commercial producers will swear up and down their cows average about 1,200 lbs. or less. That's exactly what those cows did average once upon a time, too.

“If we use feedlot exit weights as a base and the relationship between hot carcass weight and mature dam weight, the estimated mature weight of the 1990 U.S. cowherd was 1,228 lbs. compared to 1,386 lbs. in 2010,” says Justin Waggoner, Beef Systems Specialist at Kansas State University (KSU). “Therefore, using 1,200 lbs. for a cow in 1990 was accurate, but today using a weight of 1,350 or 1,400 lbs. would be more appropriate.”

Waggoner made those comments in the most recent KSU Beef Tips newsletter.

A couple of years ago, I ran the numbers, too. I assumed that USDA average slaughter cow weights should at least illustrate the trend in mature cow weights, even though both beef and dairy cows are included in the data.

By that measure, average cow carcass weights increased 86 lbs. from 1994 to 2008 (536 to 622 lbs.). Figuring that commercial grading cows dress at 55-60 percent, and that Canners dress at 40-46 percent, that meant the live weight of those cows increased 150-200 lbs. on average. In order to put those weights on par with their production peers, some would argue that you'd need to add another 80-120 lbs. (1.0-1.5 Body Condition Scores).

At the time I ran the numbers, I quizzed Twig Marston about the nutritional implications of creeping mature cow weights. He was an extension beef cattle specialist with Kansas State University at the time and now holds the same position with the University of Nebraska.

Generally speaking, Marston explained that every 100 lbs. change in cow body weight changes the requirement for Total Digestible Nutrients by 0.65 lbs. per day.

So, cows that are 150-200 lbs. heavier today require another 97.5-130 lbs. of TDN per year. That's before you consider specific additional requirements for energy and protein.

Likewise, Waggoner made his recent observation to illustrate how it is that stocking rates can creep ahead if yesteryear's cow weights are utilized.

“If the total number of animals per unit of land, per month has not been adjusted, then the pounds of animal per unit of land may have increased by about 150 to 200 lbs. per animal…” Waggoner says. “…For example, a particular pasture supporting 200 cow-calf pairs in 1990, with the cows weighing about 1,200 lbs. each, equals a total stocking number of 240,000 lbs. If the number of pairs turned out every spring has not been changed, the actual stocking number today would be 270,000 lbs., an increase of 12.5 percent. This could have serious implications on long-term forage quality and quantity. To get a comparable stocking rate today versus 1990, using 1,350 lbs. cows, only about 178 pairs should be placed on the pasture.”

Feed costs and cattle prices being what they are, the fallout from inadequate nutrition as well as the cost of feeding larger cows takes on a whole new meaning.

It's about Efficiency, not Size

That's not to say that smaller cows are necessarily more efficient than larger ones or visa versa. Efficiency comes in all sizes relative to the resources. It does say, however, identifying and managing the most efficient is worth more than ever.

Researchers with the King Ranch Institute for Ranch Management (KRIRM) examined how to determine the right-sized cow for efficiency. The researchers were Jennifer Johnson, J.D. Radakovich and Barry Dunn.

“The biology of maintenance energy requirements dictates that while a larger cow will consume more food than a smaller cow, its additional feed requirements, as a percentage, are less than its additional weight, as a percentage,” say the researchers. “For example, though a 1,200-pound cow weighs 20 percent more than a 1,000-pound cow, the feed requirements of the heavier cow are only 13 percent more.”

Yes, for the same amount of feed resources, you can run more cows of smaller sizes or fewer cows of larger sizes, in general terms. Based on inherent cow efficiency, though, either size can provide the most net return.

For that matter, when all of the costs are considered, running more smaller cattle can actually cost you more total dollars.

The folks from KRIRM pointed out, “If herd size is adjusted correctly, switching from larger to smaller cattle will not increase total fixed costs or feed costs, but will increase variable costs, as well as investment costs in terms of cattle inventory.”

In other words, for a given feed resource, the cost is the same, as well as the fixed costs of an operation. But, inventory costs increase with the number of head, as do variable costs such as bulls required, marketing cost and the like.


Selecting for Efficiency

All of this is why there's been so much focus on feed efficiency in the cow herd for the past 8-10 years. Once the primary domain of feedlots, cow-calf and seedstock producers began trying to figure out how feed efficiency could or should be measured at ranch level, whether it was heritable, and if so, what it was worth.

Ty McDonald at Montana State University did an admirable job of stating the definition and opportunity in his Masters thesis last year, entitled "Searching for the Ultimate Cow: The Economic Value of RFI at Bull Sales."

“Selecting cattle that consume less feed without production losses can increase the profitability of cow/calf producers by reducing input costs. However, genetic selection based on historical measures of feed efficiency or feed to gain ratios (F:G) is unable to improve this trait because of correlations between feed efficiencies and gain traits,” McDonald wrote. “Residual feed intake (RFI) is an alternative measure of feed efficiency that is independent of body weight (BW) and growth traits. RFI is the difference between an animal's actual feed intake and expected feed intake. For example, an animal that consumes 3 lbs. less feed than expected would be assigned a RFI of -3 and is considered more feed efficient than those with larger RFI measures.”

Definitive answers are still a ways off, but folks have figured out RFI is a lowly to moderately heritable trait. There's plenty of genetic variation, too, meaning that progress can be achieved through selection.

John Patterson, extension beef specialist at Montana State University explained at this month's annual Beef Improvement Federation meeting that at the Midland Bull Test Sale in Montana, buyers paid $125 more for every pound of RFI improvement last year. They paid $480 for it this year.

The reason has nothing to do with calves out of those bulls being worth more money to a feedlot. Increased feed efficiency is certainly worth more in the feedlot, but it can be derailed so many different ways that buyers are unlikely to pay more for it in conventional marketing channels. Instead, at least theoretically at this stage, the value comes in what RFI means in daughters of those bulls. If they produce as much with less feed, that means costs are lower and that more cows can be run with the same resources.

Others are looking at different efficiency measures. For instance, according to research conducted by Bob Wettemann, a Regents Professor at Oklahoma State University, there is typically a 25-30 percent variation within herd for the amount of energy individual cows require to maintain body weight during late gestation.

The crux of Wettemann's research is trying to find bio-markers that would allow identification of the cows that require the least maintenance energy to maintain body weight. Wettemann points out RFI is an effective way to get at the efficiency of growing cattle, but it doesn't get directly at maintenance efficiency in cows.

Like cow weights, though, whatever the ultimate measure of efficiency used for genetic improvement, accuracy, aiming at what we think we are, will be the key.

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