The yellow pigmentation of bull semen and its content of riboflavin, niacin, thiamine and related compounds

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Abstract
The seminal plasma from a number of otherwise normal Friesian bulls was quite yellow and the evidence suggests the characteristic is hereditary and may behave like a Mendelian dominant. The yellow pigment has been identified as riboflavin which occurred at an average concentration of 19 [mu]g/ml in pigmented samples compared with 0.5 [mu]g/ml in colorless samples. Similar amounts of chloroform-soluble fluorescent material were also present. The niacin, thiamine and fructose levels of the yellow samples were not significantly elevated. Exposure to light caused the yellow semen to fade and this was accompanied by the breakdown or riboflavin to lumichrome. Ribitol, which might be expected to form in the process, is not oxidized by full spermatozoa. When riboflavin was added to normal white ejaculates at a concentration of 20 [mu]g/ml it decreased the oxygen uptake and decreased the motility of the spermatozoa.