Issue 5, July 2000
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Nutrition and Immunity: Looking for Connections

A strong immune system can make the difference between fighting off a passing virus or succumbing to illness. It can mean higher milk production, healthier offspring and better growth. But how can producers help strengthen their animals’ immunity?

Researchers at several ARS laboratories are working to find out. The scientists focus on the links between nutrition and immune function, because feed-based strategies are some of the most practical for producers to implement. In addition, these strategies offer a rapid means of getting newer scientific principles of animal health from the laboratory into the hands of producers and extension agents.

Some links between nutrition and disease are direct. For example, ARS researchers at the National Animal Disease Center (NADC) in Ames, IA, showed that high potassium levels cause milk fever in cows--not calcium as previously thought.

More often, though, immunity and nutrition have less tangible connections. While immune function appears depressed in dairy cattle just before and after giving birth, the reasons are not well defined.

In beef cattle, researchers at the Growth Biology Laboratory in Beltsville, MD, discovered several years ago that high-protein diets curbed an overproduction of cytokines observed with poor or unbalanced nutrition. While cytokines are necessary hormones, overproduction can cause shock and cardiopulmonary failure.

More recently, Beltsville researchers found that changes in metabolic hormones and cell processing of specific nutrients interplay to regulate the amount of chemically active “free radicals” produced in cells. These free radicals can change the activity of otherwise normal proteins and, in turn, alter metabolism and increase the rate at which healthy cells deteriorate. Antioxidant vitamins can reduce free radical impact. Ongoing studies will help define the best mix of antioxidants in cattle feed during anticipated periods of stress, such as birth, weaning, or turning out to pasture in the spring.

ARS’ ability to hold animals long term helps researchers study these complex interactions. For instance, NADC scientists can infuse dairy cattle with nutrients and perform sophisticated blood assays while maintaining them in the milking barn. That’s crucial for understanding the immune system changes that take place immediately before and after cows give birth. The Ames location also has quarantine facilities and a veterinary staff available to handle disease research.

At Beltsville, researchers can team with the Nutrient Conservation Laboratory and perform indirect whole body calorimetry on cattle. This allows them to monitor whole-body oxygen consumption and oxidation as a function of changing nutrient composition and response to simulated disease stresses.

At the Aquatic Animal Health Research Laboratory in Auburn, AL, ARS scientists are expanding their disease and parasite studies to define the effects of nutrition, feed and feeding on immunity and disease resistance in fish. They hope to develop feeds that optimize not only growth and feed efficiency but also for improving the health of catfish and other warmwater aquaculture species.

ARS has recently restructured its national programs. The animal nutrition component now resides under Food Animal Production.

For more information, contact:

Ted Elsasser, Beltsville, MD (beef cattle)
Jesse Goff, Ames, IA (dairy cattle, periparturient diseases)
Chhorn Lim, Auburn, AL (fish)

Research Briefs

A new, ARS-developed laboratory method for growing macrophages in tissue culture may help researchers studying the virus that causes porcine reproductive and respiratory syndrome. The virus replicates inside macrophages.
Neil Talbot
(301) 504-8216

Special ARS chicken breeding lines--developed with varying degrees of genetic resistance to viral-induced lyphoid tumors--are now stored in Fort Collins, CO, and East Lansing, MI, as the first accession in ARS’ National Animal Germplasm Program.
Harvey Blackburn
(970) 495-3200
Larry Bacon
(517) 337-6828

Substantially more nutrients from silage should be available to dairy cattle in the Southeast, thanks to a new corn germplasm line with improved digestibility released by ARS.
Neil Widstrom
(912) 387-2341

ARS and University of Arkansas scientists have selectively bred four generations of chickens with low or high resistance to ascites, a fatal heart condition. By defining the differences between the two groups, they hope to find a treatment or cure.
Janice Balog
(501) 575-6299

ARS researchers discovered leptin in chickens using a new technique. The protein regulates appetite and energy expenditures.
Christopher Ashwell
(301) 504-5061

The International Chicken Genome Mapping Project
--in which ARS partici- pates--released its latest draft of the chicken genome map. This map could help breeders increase disease resistance and lessen dependence on antibiotics.
Hans Cheng
(517) 337-6828

Hay made from selenium-enriched canola may provide a new source of the essential nutrient selenium for livestock raised in deficient regions while cleaning up soil and water overloaded with this mineral.
Gary Bañuelos
(559) 453-3115

Awards

These ARS researchers have been honored recently for their achievements:

USDA Honor Awards:

David Swayne , Michael Perdue, David Suarez, Stacey Schultz- Cherry, Joan Beck, Patsy Decker, and Roger Brock, Southeast Poultry Research Laboratory, for research leading to advanced understanding of the pathobiology and epidemiology of Hong Kong H5N1 avian influenza and development of strategies to protect U.S. poultry from this disease.

Michael Ralphs, Poisonous Plant Research Laboratory, was presented with an Outstanding Achievement Award by the Society for Range Management for developing strategies to control poisonous rangeland plants, including aversion conditioning for training large animals.

John Berdahl, Northern Great Plains Research Laboratory, received an Outstanding Achievement Award by the Society for Range Management for developing improved forage grasses.

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