“…The effect of dietary penicillin on calcium absorption (Migicovsky et al, 1951), on the concentration of serum carotenoid pigments, and liver vitamin A and on the concentration of yolk biotin and folic acid (Waibel et al, 1952) suggests that the antibiotic increases (a) the amount of these nutrients available to the host or (b) the absorptive capacity of the gut wall. Either of these hypotheses explains the "vitamin-sparing" activity of antibiotics when included in diets which contain suboptimal amounts of certain vitamins (Sunde et al, 1951, Coates et al, 1951 and accounts for the observed increase in feed efficiency when antibiotics are added to simplified diets Branion and Hill, 1951).…”