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August 14, 2003

New tool helps researchers bone up on osteoporosis

WEST LAFAYETTE, Ind. – Purdue University scientists investigating osteoporosis in laying hens have shown that a noninvasive tool can monitor birds' bone strength and aid in discovering genetic information about bone disease in chickens.

Lack of calcium in chickens' food and lack of exercise can leave hens with brittle bones, said Patricia "Scotti" Hester, a professor in Purdue's Department of Animal Sciences. In addition, eggshell production leaches calcium from hens' bones. Hester and her research team found they could accurately determine bone mineral density using a technology known as dual energy X-ray absorptiometry (DEXA).

Their study is published in the August issue of the journal Poultry Science and also appears on the publication's Web site.

"The brittle bone problem has evolved gradually over the past quarter of a century," Hester said. "This is due to generally selecting chickens for increased egg numbers, and smaller bird sizes for improved feed efficiency. Also, little emphasis has been placed on selecting for skeletal integrity."

Skeletal integrity in hens also decreases during management practices used to improve shell quality and lengthen a bird's production life, Hester said. Previous studies by other researchers have found that osteoporosis accounts for 15 percent to 30 percent of total fatalities in hens.

"If we can find genes associated with osteoporosis, we can use genetic selection to improve skeletal integrity," Hester said. "We hope that this will be a way to reduce the incidence of brittle bones because of the considerable variation in bone mineral density that we've found among hens."

Various researchers also are studying other factors that contribute to brittle bones in poultry.

"Osteoporosis in chickens is an animal well-being issue," Hester said. "Breeding, diet and exercise all play a vital role in skeletal integrity of laying hens."

Her team conducted two experiments for this study of skeletal integrity. One experiment assessed bone strength in live white leghorn hens at 36, 46 and 56 weeks old, while the second experiment dealt with 38-, 48- and 58-week-old hens.

In both experiments, a third of the chickens received a low-calcium diet, a third an average diet and a third a high-calcium diet. The scientists showed that more calcium resulted in greater bone mineral density and stronger bones and that the DEXA machine could accurately record those differences.

Results of this study showed that the hens fed a low-calcium diet produced fewer eggs. The eggshells they produced also were significantly thinner and weighed less than the birds fed an average to high amount of calcium.

Though the researchers aren't specifically seeking answers to human osteoporosis, they may find some.

Evolutionary biology has shown that many of the same or similar genes are found in different plants and animals. So, studying one species often leads to information to help with research in another plant or animals. Chickens already are used for other biomedical studies, including embryo development and birth defects, because of some known gene similarities.

Last year, the National Human Genome Research Institute, part of the National Institutes of Health, placed chickens on the high priority list for sequencing of the bird's genetic makeup. The institute's program is directed at comparing genomes of plants, animals and humans to determine similarities and differences that make them susceptible or resistant to various diseases and developmental problems.

In the meantime, discovering genetic methods to lessen osteoporosis is of immediate concern to the egg industry.

Before the bone-weakening disease became so widespread in poultry, the approximately 45 million laying hens disposed of annually in the United States were sold to soup manufacturers. But osteoporosis caused so many bone splinters in meat that it couldn't be used for human consumption. Now most of the soup meat comes from broiler, or meat-type, chickens, rather than egg-laying hens.

"If the skeletal integrity of laying hens can be improved to reduce splintered bones, then perhaps the soup market can be regained at 25 cents or more per chicken," Hester said.

Many farmers now must pay to have the birds hauled away or give them away free, she said. If hens are not processed for meat, then producers need an environmentally safe and economical way to dispose of the birds once their egg-producing days are over.

The estimated U.S. annual economic loss because the egg layers aren't used for meat products is $18 million, Hester said.

Other researchers involved in the study include: Diane Moody, Purdue assistant professor of animal sciences; graduate students Melissa Schreiweis and Helenice Mazzuco; animals scientists Joseph Orban of Southern University, Shreveport, La.; and Monica Ledur of Embrapa Swine and Poultry Research Center in Concordia, Brazil.

The U.S. Department of Agriculture Scientific Cooperation Research Program, the National Research Initiative Competitive Grants Program and the State of Indiana Value-Added Grant Fund provided support for this study.

Writer: Susan A. Steeves, (765) 496-7481, ssteeves@purdue.edu

Sources: Patricia "Scotti" Hester, (765) 494-8091, phester@purdue.edu

Ag Communications: (765) 494-2722; Beth Forbes, bforbes@aes.purdue.edu; http://www.agriculture.purdue.edu/AgComm/public/agnews/

 

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ABSTRACT

The Use of Densitometry to Detect Differences in Bone Mineral Density and Content of Live White Leghorns Fed Varying Levels of Dietary Calcium

M. A. Schreiweis,* J. I. Orban,† M. C. Ledur,‡ and P. Y. Hester* – *Purdue University, Department of Animal Sciences, West Lafayette, Indiana 47907; †Southern University, Shreveport, Louisiana 71107; and ‡Embrapa Swine and Poultry Research Center, Concordia, SC 89700-000, Brazil

Densitometry was investigated as a noninvasive tool to monitor skeletal integrity in live white leghorns as an indicator for osteoporosis, a noninfectious disease resulting in mineral loss from the bone. The objectives of the experiment were: 1) to assess the ability of densitometry to detect differences in bone integrity in live white leghorns fed varying concentrations of dietary calcium and 2) to correlate densitometric scans with other bone test methods and production parameters that are sensitive to calcium concentrations in the diet. Hens were fed hypercalcemic (5.4%), control (3.6%), or hypocalcemic (1.8%) diets from 32 to 58 wk of age. A Norland densitometer was used to assess bone mineral density (BMD) and bone mineral content (BMC) of the left tibia and humerus in restrained, unanesthetized hens at 36, 46, and 56 wk of age (experiment 1) and at 38, 48, and 58 wk of age (experiment 2). Bones were excised from hens at 38, 48, and 58 wk of age for breaking strength measurements. Results from the densitometric scans showed that BMD and BMC of the humerus and tibia of live hens decreased linearly when hens consumed diets with decreasing concentrations of calcium (experiment 2). Similar trends in BMD and BMC were detected in experiment 1 at 36 wk of age using BW as a covariate. The results from the densitometric scans were comparable to those obtained from other bone tests commonly used. For example, bone breaking force, stress, and modulus of elasticity decreased linearly as hens consumed decreasing concentrations of calcium. Bone breaking force was correlated with BMD (r = 0.65, P < 0.001). We concluded that densitometry accurately measures differences in BMD and BMC in live birds fed varying concentrations of dietary calcium.

(Key Words: bone mineral density, bone mineral content, dietary calcium, White Leghorn, osteoporosis)


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