Not Your Daddy's Genes
Mar 1, 2010 12:00 PM, By Wes Ishmael, Contributing Editor
U.S. Meat Animal Research Center data shows remarkable selection pressure has upended breed stereotypes.
A show of hands: How many think Simmental cows have a larger mature size than Angus and Hereford?
If your hand's in the air, you've got plenty of company, but you also happen to be dead wrong.
Researchers at the U.S. Meat Animal Research Center (USMARC) found that F1 cows sired by Angus weighed 1,410 lbs; those sired by Hereford weighed 1,419 lbs; and those sired by Simmental weighed 1,404 lbs. These were five year-old cows born in 1999 and 2000 by sires sampled in 1998, part of Cycle VII of USMARC's ongoing Germ Plasm Evaluation Program.
The mature weights of the three English breeds in Cycle VII ranged from 1,409 lbs. to 1,419 lbs., adjusted to a Body Condition Score of 5.5. For the cows sired by four of the most heavily used Continental breeds, the range in mature weight was 1,371 lbs. to 1,404 lbs. (Table 1).
"In the 1970s, Continental breeds had greater growth rates and were heavier at weaning, yearling and maturity. Today, British breeds in the U.S. are comparable to Continental breeds for these traits," explained Larry Cundiff to New Zealand producers in 2007. "The lack of differences among breeds for cow weight and height contrast sharply with comparisons made 30 years earlier when cows by Continental European sire breeds were on average 4.5% taller and about 4.8% heavier than those by British sire breeds." Cundiff served as research leader of USMARC's Genetics and Breeding Research Unit for better than three decades.
Cowboy math also supports the notion that
commercial cow weights have increased at least 200-300 lbs. since 1994.
"We think of British breeds being moderate-sized and moderate in lactation, and that's not the case anymore when you look at genetic trends," says Bob Weaber, University of Missouri Extension beef cattle specialist.
Phenomenally steep trends
When you ponder the genetic trends for the most heavily used breeds since the 1970s, USMARC research geneticists Mark Thallman and Larry Kuehn say what strikes you most is the staggering increase in yearling growth and milk expected progeny difference (EPD), especially for the Angus breed.
According to graphs Kuehn assembled, the seven most heavily used beef breeds have all increased yearling growth — as measured by mean across-breed yearling growth weight EPD, adjusted to an Angus base, using USMARC across-breed EPD adjustment factors estimated by Kuehn (Figure 1). But none has been steeper than Angus, growing from among the lowest in 1985 to the second highest in 2007, just below Charolais and just above Simmental.
The same general trend can be seen for milk (Figure 2), with Angus growing from third lowest to second highest. Meanwhile, breeds like Gelbvieh and Simmental, which already had high levels for milking ability, have stabilized the trend or decreased it by choice.
To a lesser extent, the same trend describes weaning weight EPD (Figure 3). Plus, almost all of these breeds decreased birth weight trends during the past decade, especially Gelbvieh and Simmental (Figure 4).
"It's a great example of the utility of EPDs and what can be achieved by using them for selection," Weaber says.
The trends in growth also underscore the rational response of seedstock producers to an industry that continues to reward pounds above all else.
"Demand from feeders and packers to make cattle heavier drives the trend for growth. Also, in the seedstock industry, it's too easy to fall into the trap of trying to be the best at something and selecting for extremes," Weaber explains.
"The growth in milk EPD is driven less by packers and feeders; it is producers seeing increased milk as a means to increase weaning weight, and seedstock producers chasing the numbers without recognizing the impact it has on nutritional demands."
But, Weaber cautions viewing breeds through yesterday's reality poses risk.
"I'm not going to presuppose the right size and lactation for an individual producer. What concerns me are the misconceptions that may exist relative to management," Weaber says. "If producers are using breed stereotypes based on the past in management, they may be setting up the genetics for failure if they're managing the cattle to those stereotypes."
How much is too much?
Though a tribute to breeder ability and commitment,
the spectacular growth in genetic trends begs the question about whether a point comes where increasing the genetic potential in particular trait areas costs more than it returns.
"It can be useful to increase the genetic trend in trait areas as long as the profitability associated with them continues to increase," Kuehn says. "One reason they don't continue to be profitable is because of the antagonisms that exist between traits."
Thallman adds that "the complicated answer is that to really identify where we cross that line requires merging economics and genetics together. The answer will always depend so much on environment, management and marketing. It will always depend on where your operation fits within the production system."
Some work's been done to create prediction models and decision-support tools that would lead to the answer, but plenty of work is left to be done.
"The easier answer is that we could worry a little less about what the antagonisms might be if we could do a better job of measuring the other traits that impact it," Thallman says. Think here of fertility, cow longevity and the like.
For that matter, think about mature cow size.
"I think increased mature cow size resulted from increased selection for growth without also selecting to maintain mature weight," Weaber says. "Mature cow size is highly heritable, but it's difficult to get producers to collect the data."
In other words, to truly bend the growth curve — low birth weights and small to moderate mature size with rapid growth — would require selection tools for mature size. A few breeds have EPDs for mature size.
Overall, Weaber believes, "for many breeds, the genetic potential is above where it needs to be, especially for mature weight. A growing question among seedstock producers revolves around determining the optimum level for particular production environments, rather than how much more can be achieved in a trait. They're asking themselves about the costs associated with higher levels of production and how that's best utilized given their resources."
Weaber emphasizes, however, "EPDs for growth aren't responsible for big cows, producers are. And, EPDs — the tools used to select for more growth and larger cows — can be used with discipline to decrease and optimize mature cow size."
Keeping up with the Joneses
Perhaps as striking as the level of increase in genetic trends is the direction. In the world of genetics, where variation and differences are an asset rather than a liability, converging trends suggest breeds are becoming more alike than different.
Based on the trends, Thallman says, "they all appear to have the same target in mind, though they began the journey at different places relative to that target."
In other words, they're all chasing more weaning and yearling growth, more milk and trying to at least hold birth weight constant.
Looking at the convergence of breeds according to genetic trend, Kuehn explains,
"I think a lot of them are coming at it from the standpoint of trying to be an all-purpose breed rather than accentuate their breed differences."
Producers can agree or disagree with the genetic trends of particular breeds, but the rapid change in these trends suggests they'd better keep track of where the breeds exist along that trend.
"The point is that breed differences are not static; they change over time," Thallman says.
Table 1. Mature cow weights of F1 cows by sire* Breed 5-year-old-weight, lbs.**
Hereford 1,419
Angus 1,410
Red Angus 1,409
Simmental 1,404
Gelbvieh 1,323
Limousin 1,391
Charolais 1,371
*Least squares means by breed of sire for weight of F1 cows at 5 years of age
**Weights adjusted to body condition score 505
Source: U.S. Meat Animal Research Center, Germ Plasm Evaluation Program, Cycle VII
http://beefmagazine.com/genetics/beef-n ... -20100301/
