Abstract
THE report by Barnett and Bird (1956) concerning a standard chick assay for unidentified growth factors (UGF) activity of crude materials adequately illustrates the fact that the presence of such factors in certain feedstuffs has been well established. Growth responses have been dramatic and fairly consistent when semi-purified type rations have been employed. However, when practical type rations are supplemented with UGF sources, the growth response has been somewhat variable (Camp et al., 1957; Summers et al., 1959a,b). Some workers have attributed the lack of a response to UGF sources to be due to the presence of antibiotics in the ration (Combs et al., 1954a; Barnett and Bird, 1956). Scott and Jensen (1952) suggested that part of the antibiotic response may be caused by the sparing effect on UGF. Wisman (1960) concluded that arsonic acids allow the UGF activity in fish byproducts to be more fully expressed, rather than to …
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