March 15, 2014


 Gaining weight

Livestock are bigger now at slaughter than in previous decades 

By Greg Cima
Posted Feb. 27, 2014

Cattle are about 200 pounds heavier when sent to slaughter today than they were in the 1980s, now reaching a mean weight of 1,300 pounds
Turkeys have gained a mean of 10 pounds in that period, up from 20 pounds to 30. They averaged 17 pounds each in the 1960s.

Figures from the Department of Agriculture indicate that pre-slaughter weights of livestock species have been increasing since at least the 1920s, and some of the largest gains have occurred in the past 25 years. The USDA’s monthly data on livestock weights, averaged by decade, show that, since the 1980s, mean hog weight has increased by 8 percent, mean sheep and lamb weights by 21 percent, mean broiler weight by 38 percent, and mean weight of other chickens by 27 percent.

Kenneth H. Mathews, PhD, an agricultural economist for the USDA Economic Research Service, said U.S. beef industries today produce almost the same amount of meat they did with the peak cattle population of the mid-1970s, despite having a third fewer cattle. He thinks genetic selection likely is the largest factor in the size increases, along with changes in technology, nutrition, care, and management. 

Faster gain, larger at slaughter

The weights recorded by the USDA ERS at slaughter show faster growth, but not always a corresponding change in the proportions of adult animals. Dr. M. Gatz Riddell, executive vice president of the American Association of Bovine Practitioners, said cattle’s mature weights, rather than slaughter weights, likely have not increased since introduction of more heavily muscled cattle breeds from Europe during the 1970s or 1980s.

“If you look at a mature 5-year-old bull or cow from the breeds in the same two decades, they probably have not changed,” he said.

Instead, the cattle slaughtered at 12 or 18 months of age have body proportions similar to those of their predecessors, but more muscle relative to fat, Dr. Riddell said. 
(Courtesy of National Turkey Federation/Copyright Iowa Turkey Federation)
Dr. Dan Thomson, a professor of production medicine and epidemiology and director of the Beef Cattle Institute in the Kansas State University College of Veterinary Medicine, said the rise in slaughter weights is not only a result of selection for factors such as increased lean body growth and more efficient growth but also of sorting that better divides cattle into groups slaughtered when they reach ideal weights.

Steve R. Meyer, PhD, president of Paragon Economics and a consulting economist for the National Pork Board, said pigs are still slaughtered at 6 or 7 months of age, but they are heavier at that age because they grow more quickly. He said the changes in hog slaughter weights were driven by economics and limited by factors such as the genetic ability of an animal to convert feed into lean meat instead of fat.

Keith Williams, vice president of communications and marketing for the National Turkey Federation, said that, in response to Americans’ increased desire for turkey meat starting in the 1970s, turkey owners bred in favor of turkeys with broader breastplates as well as for stronger legs that can support the larger birds.

Adapting with the animals

Dr. Riddell said cattle raised for beef carry the added weight about three to six months of their 12- to 18-month lives. While cattle with substantially higher mature weights would be at risk for joint problems, Dr. Riddell does not think the short period they are carrying the added weight is cause for concern. He also noted that lameness and joint disease are affected by diet.

“As these animals are growing faster and converting feed more efficiently, if we weren’t doing things like trying to minimize digestive upsets, we could expect more foot problems,” Dr. Riddell said. 
Click on image to enlarge 
Cattle veterinarians also know that the larger animals are at greater risk of injury when they become stressed, Dr. Riddell said.

“If we kept doing the things we had been doing for the last 30 years, and the cattle got bigger, the way we handled them can lead to problems,” Dr. Riddell said. He later added, “Because we’ve increased our skills in handling them and we’ve increased our knowledge base in how we need to have good footing for them that is safe and healthy for their feet, we have counteracted some of the potential negatives.”

Breeding programs also include efforts to select for calmer animals, he said.

As pigs have increased in size, companies have scrutinized stocking densities and tried to make sure facilities used by the animals, such as loading chutes and alleys, still work well, said Meyer of the pork board.
“The heavier pigs today are probably handled better than they used to be, because we know more about it,” he said.  
Williams, of the National Turkey Federation, said he thinks turkeys grow more quickly, in part, because they have less stressful lives than did their predecessors that were more exposed to weather changes, predation, and communicable disease, and because turkeys now are given continuous access to food and water.
Kurt D. Vogel, PhD, an assistant professor who teaches animal welfare and physiology at the University of Wisconsin-River Falls, said he worked in beef cattle slaughter facilities at the start of his career, and he noticed that the mean weight of carcasses already was higher than what he was taught in school. But he has not seen changes in cattle behavior or mortality associated with weight gain, although he said mortality is known to increase among turkeys and chickens that exceed certain weights.

“In all cases, care from vets and farm employees is very important, regardless of the size and age of the animals,” he said. 

Breeding’s potential

Temple Grandin, PhD, a professor of animal science at Colorado State University and an author of animal welfare standards, said she is concerned that livestock are being pushed beyond optimal production.
“I think one of the biggest animal welfare issues in the future is going to be what I’m going to call ‘biological system overload,’” Dr. Grandin said.

In the second edition of “Genetics and the Behavior of Domestic Animals,” published in 2014 and edited by Dr. Grandin and Mark J. Deesing, a design consultant for Grandin Livestock Handling Systems, they wrote that selecting animals for production traits alone will result in unintended harm to the animals. The book describes a “metabolic drain” on Holstein cows that produce twice as much milk as cows 30 years earlier, chickens that are “spent” after a year laying eggs, and declines in relative heart and lung sizes among broiler chickens that reach market weight in less than half the time of their ancestors a century earlier.

Dr. Grandin said in an interview that she is not suggesting that the country return to raising “1950s-style animals.” Instead, she said that pushing animals toward a goal requires trade-offs, with energy from feed divided among needs, whether to grow, fight disease, produce milk, or grow feathers. And she thinks livestock industries, especially the dairy and egg industries, are approaching limits on acceptable trade-offs favoring increases in production over increased stress.

As an example, Dr. Grandin cited pectoral muscle necrosis, which she said can occur in turkeys and broilers when fast-growing muscle outstrips its blood supply. Noninfectious hoof problems seem to be more common among dairy cows, she said, and larger pigs are more likely to become fatigued than smaller pigs if they experience rough handling. She also has felt flimsy feathers on egg-laying hens, which she noted can also develop osteoporosis and bone fractures.
 “I think one of the biggest animal welfare issues in the future is going to be what I’m going to call ‘biological system overload.’
Temple Grandin, PhD, professor of animal science at Colorado State University and author of animal welfare standards
But Dr. Grandin noted that industries have made changes when problems have emerged. Lameness was a more substantial problem in pigs about 10 years ago, but since then, she said the pork industry has implemented lameness assessments to reduce the problem.
She also said livestock industries can breed animals and change practices in ways that increase strength or correct problems. She recalled visiting a slaughter plant where half of arriving pigs were lame, a problem she attributed to a genetic condition affecting the animals’ feet and legs that was exacerbated by administration of more-than-ideal doses of a beta-adrenoceptor agonist. Culling boar lines and halving the drug’s dosage corrected the problem, she said.
Joy A. Mench, PhD, a professor of animal science at the University of California-Davis, said selection for rapid growth in broilers, which reach market age in as little as six weeks, has caused negative health consequences such as skeletal and cardiovascular disorders. But the broiler industry has, over the past decade, made improvements by selecting for attributes such as walking ability and improved health.  


 ​(Courtesy of USDA ARS/Photo by Stephen Ausmus)

She said selecting for increased growth rate also selected for increased appetite, which has become a welfare concern in breeding stock. Those birds will become obese and unable to reproduce if given access to as much food as desired, but the feed restrictions leave them hungry. Efforts to supplement feed with non-nutritional substances have not been effective.

Dr. Kate Barger, director of animal welfare for broiler producer Cobb-Vantress, provided a company statement indicating breeder companies balance production, health, and welfare, as demonstrated through improved quality of life and fewer birds euthanized along with improvements in fertility rate, feed efficiency, and rate of weight gain. Selection of a particular processing weight is less important than managing broilers to ensure optimal health, well-being, and development.

The opening chapters of the 2003 book “Poultry Genetics, Breeding and Biotechnology” similarly describe unintended negative consequences of selection—such as metabolic disorders and skeletal defects—but also indicate selective breeding can be an instrument to improve animal well-being. The book’s first chapter indicates the growth rate of broilers has roughly quadrupled since commercial breeding began in the 20th century, and at the time of publication, broiler producers had been trying to balance selection pressures to counteract problems.

“The body composition of the birds has changed dramatically, especially the relative size of pectoral muscles,” the book states. “Although commercial breeding programmes have been successful in counteracting this basic imbalance by genetic improvement of leg strength and other aspects of general livability such as susceptibility to ascites, there is no doubt that commercial broilers today are showing higher mortality and higher susceptibility to suboptimal management of nutrition and environment than broilers that have been selected less extremely for efficiency and meat yield.”

Asked about the risk that livestock owners would overshoot the limits of animals’ potential, Dr. Meyer said he has confidence in those owners’ abilities to select for production within acceptable limits and continue to provide benefits.

“I don’t see it slowing down any,” Dr. Meyer said.