David Christensen has had a wide-ranging influence on Canadian agriculture. His impact has resulted from teaching nutrition and dairy management to undergraduate, graduate, vocational and veterinary students at the University of Saskatchewan. He has also been widely sought as an international consultant in over twenty countries in Africa, Asia, Central America, and the Middle East. Christensen's international development activities were recently recognized when he was awarded the International Animal Agriculture Award in 1998 in Seoul, Korea by the World Congress of Animal Production, and by the J.W. George Ivany Internationalization Award in 1999 from the University of Saskatchewan. Christensen earned a BSA at the University of Saskatchewan in 1948 specializing in Animal Science, an MS in Agriculture in 1952 at the University of British Columbia, and a PhD from Oregon State University in 1955. Early in his career, he helped establish the principles of feed testing in Saskatchewan, bringing scientific nutrition information and ration formulation to the farm. In response to the enormous growth in the use of corn silage in the United States, he developed ensiling techniques and feeding systems for dairy and beef cattle based on cereal silage, which have been widely adopted in western Canada. In the late 1970s, Christensen was one of the first nutritionists to appreciate the economic impact of trace mineral deficiencies in western Canada: trace mineral supplementation is now widespread, primarily as a result of a ten-year research program.
The dehydrated alfalfa industry in western Canada developed markets and expanded production based on Christensen's research and recommendations for use of “dehy” in ruminant rations. More recently, Christensen has been active in the development of new, high-value feedstuffs based on Canadian feed ingredients for use in domestic and international markets. His research and expertise in this area were critical to the development of new export markets for such sectors of Canadian agriculture as the canola, flax, alfalfa and sunflower industries. In 2001, Christensen received the Distinguished Researcher Award from the University of Saskatchewan. In addition to teaching, research and extension activities, Christensen has served Canadian agriculture by participating on numerous boards and committees such as the Saskatchewan Dairy Association, British Columbia Department of Agriculture Dairy Project, Prairie Feed Resource Centre, Dairy Farmers of Canada, the Agricultural Institute of Canada International Development Committee, Saskatchewan Livestock Association, Saskatchewan Advisory Committee on Animal Nutrition, and Canadian Society of Animal Science. He is a Fellow of the Agricultural Institute of Canada.