Riboflavin is not required in the diet of adult ruminants per se because of rumen synthesis. Apparently no response to supplemental riboflavin has been reported in animals with a functional rumen, although tests with present-day levels of milk production and growth may be warranted. Miller et al. (1986a) reported that cattle on a concentrate-silage diet would synthesize approximately 38 mg of riboflavin in the rumen. A dairy cow producing 42 kg (92 lbs) of milk per day loses about 72 mg of riboflavin in milk alone, much more than is consumed in the diet.
Riboflavin deficiencies have been demonstrated in young ruminants whose rumen flora is not yet established. Riboflavin deficiency results in redness of the mouth mucosa, lesions in the corner of the mouth and around the edges of the lips and navel, loss of hair, and excessive tear and saliva production (Radostits and Bell, 1970). Non-specific signs are anorexia, chronic diarrhea and reduced growth.