Harold Guilbert was born in Ohio but spent his boyhood on a cattle ranch near Sharon Springs, Kansas.
He graduated from Kansas State College with a Bachelor of Science in 1920, and was an Instructor in Animal Husbandry at the college until 1924 when he also received a Master of Science degree. Harold came west in 1924, joining the staff at the University of California at Davis as a Junior Animal Husbandman. He progressed to Professor by 1945 and served as acting head of the Department of Animal Husbandry in 1951.
Professor Guilbert's specialty was beef cattle production. His studies of animal nutrition and its relationship to reproduction in the bovine at the San Joaquin Range led to significant contributions to the knowledge of protein and vitamin A requirements for livestock. He was particularly interested in the mechanism of growth of beef animals and developed a system of numerical assessments of standards of excellence that was widely adopted in the field. The manual Beef Production was one of his collaborative efforts.
He was very active in the work of the Western Section of the American Society of Animal Production, serving as its president in 1941.