A new genetic sequence specific for Mycobacterium paratuberculosis plays a key role in new tests now under development to detect Johne's disease, a $1.5 billion a year problem for U.S. dairy producers. The gene sequence for detecting M. paratuberculosis--the culprit behind Johne's disease--was identified by ARS researchers. Johne's disease cuts milk production, animal weight and reproduction. The new DNA-based test will report results in only 2 to 3 days. Current tests search for antibodies that aren't usually detectable until cows have been infected for several years, giving M. paratuberculosis a costly headstart in the herd. Early diagnosis is critical to eliminating the disease because the primary control method is removal of infected animals from the herd. Infected animals may not show signs of disease, but can still pass the organism to healthy animals.
National Animal Disease Center, Ames, IA
Judith H. Stabel, (515) 239-8304, jstabel@nadc.ars.usda.gov

A new 10-minute test rates the sexual adequacy of male swine as reliably as two earlier tests, and with less expense. The new test requires only one female swine to rate a boar's sexual behavior. The other two tests require more females or take much longer. ARS scientists compared results for 20 purebred boars of various breeds with each test. Whether a boar rated high, intermediate or low in sexual behavior, its conduct was consistent in all three tests, the scientists found. The new test involves injecting a neutered female swine with a hormone, estradiol benzoate. This induces estrous behavior that makes her receptive to mating. In one of the earlier tests, each boar was penned for 10 minutes with three female swine--two estrous-induced and one nonestrous animal. In the other previously existing test, each boar was kept for nearly 5 days with a similar group of test females.
U.S. Meat Animal Research Center, Clay Center, NE
Ronald K. Christenson, (402) 762-4192, christen@marcvm.marc.usda.gov

The United States is the world's leading exporter of dairy bull semen. To maintain this valuable market share, ARS scientists evaluate about 128,000 U.S. bulls based on data collected from more than 20 million of their daughters. Each year, the scientists process and evaluate millions of new records from these female offspring that indicate important genetic traits, such as milk production and composition. The production data are initially collected by the National Dairy Herd Improvement Association. The researchers forward their results to INTERBULL--the independent International Bull Evaluation Service. Twice each year, INTERBULL evaluates for its 20 participating nations nearly 90,000 recent bulls from 6 breeds of dairy cattle. INTERBULL's long-term objectives are to improve milk yield and quality, increase resistance to diseases like mastitis, and preserve genetic diversity. But its short- term objective is to rank the bulls, enabling breeders to select the world's best bulls to sire daughters based on objective criteria. American bull semen continually ranks high on INTERBULL evaluations, reflecting the United States' ability to stay competitive in breeding markets internationally. Export sales of U.S. bull semen exceed $60 million a year.
Animal Improvement Programs Laboratory, Beltsville, MD
Rex L. Powell, (301) 504-8334, rexpowel@ggpl.arsusda.gov

A scientific first at ARS--deleting genes from the mammary gland cells of mice--could have implications for milk production in cows and for breast cancer in humans. The scientists developed transgenic mice in which they can delete some genes from mammary gland cells. Until now, gene deletion was not possible in mammary glands of livestock. The transgenic mice were born with new genes--inserted by the researchers--known as a "cre-lox recombinase system." Cre-lox recombinase genes originate from bacterial viruses. In such viruses, these genes can naturally cut out DNA sequences. The new approach is directed toward learning to delete specific genes, such as milk protein genes, from cells of a cow's mammary glands. Scientists can then determine whether specific genes affect mammary gland functions. The technique also could help medical researchers define genetic contributions to breast cancer, by allowing them to insert or delete various genes in laboratory cell cultures and study them.
Gene Evaluation and Mapping Laboratory, Beltsville, MD
Robert J. Wall, (301) 504-8362, bobwall@ggpl.arsusda.gov

Feeding dietary iron to channel catfish does not protect them against dying from enteric septicemia of catfish (ESC) caused by the bacterium Edwardsiella ictaluri. This bacterial killer costs catfish farmers about $50 million a year in losses. ARS scientists are evaluating channel catfish diets for optimum growth and disease resistance. One ARS study focused on dietary elements, their interactions and feeding management to enhance immunity and disease resistance against ESC. The finding: While iron supplements improved growth rate and survival of catfish in general, they did not protect fish from ESC. The scientists will continue to search for nutritional factors that could improve fish resistance to ESC. Up next: a study of dietary protein levels and their interaction with vitamin B6 and energy.
Fish Diseases and Parasites Laboratory, Auburn, AL
Chhorn Lim/Phillip Klesius, (334) 887-3741, limchh@mindspring.com/klesiph@vetmed.auburn.edu