After earning a Bachelor of Science degree in Animal Science from West Virginia University and a Master of Science degree in Animal Science from Rutgers University, he served as an associate professor and extension specialist in animal science with Rutgers/Cook College and the Rutgers Cooperative Extension Service for over 37 years.

Kniffen served as President of the New Jersey Angus Association, Secretary-Treasurer of the Sheep Breeders Association, Director of the New Jersey Beef Industry Council and member and secretary/treasurer of the New Jersey Polled Hereford and Angus Associations. Kniffen was also an active member of the New Jersey Hampshire Association and the National Cattlemen's Beef Association.

Cattle, sheep and swine producers all along the East Coast called upon Kniffen for advice and expertise. Here in the Garden State Kniffen provided guidance and assistance to two generations of livestock producers. He was instrumental in creating and implementing the Spring and Fall Feeders Calf Sales, the New Jersey Wool Pool, the State 4-H Baby Beef Show and Sale and the New Jersey State 4-H Lamb Show and Sale. He judged many local 4-H youth livestock shows as well as regional and national events.

He became a Professor Emeritus at Rutgers University and was honored by the establishment of the Don Kniffen Annual Beef Showmanship Award.

During World War II, from 1944 to 1946, he served in the United States Navy as a Gunner's Mate, Third Class, on the USS Noa.

Kniffen was a devoted husband to Gail and father to Donald Jr. and Daniel. The State Board of Agriculture was deeply saddened by the death of Donald M. Kniffen, Sr., and the entire agriculture community mourns the loss of this dedicated advocate.

In recognition of his service to the livestock industry of New Jersey during his distinguished career, the State Board of Agriculture honors Donald M. Kniffen, Sr., posthumously, with its citation for Distinguished Service to New Jersey Agriculture.