There are many reports in the literature, some of them considered in a recent series of reviews (Schultz, Day & Sinnhuber, 1962), demonstrating that feeding with rancid fat can in some circumstances have growth-depressing or other unfavourable effects on experimental animals. Thus the practice has grown up of characterizing the fatty fraction of animal feeding-stuffs by simple procedures (in the past these have been the determination of free fatty acids and peroxide value) and rejecting materials that gave values above certain limits.However, there seems no evidence that free fatty acids as such are harmful to animals (though they may reflect the existence of mouldiness in certain classes of materials); moreover, the permitted levels of 'peroxide' have been only a small fraction of the high levels found harmful in diets under experimental conditions. It is known that the presence of oxidizing fat in the diet may cause severe losses of easily oxidizable vitamins, particularly E and A, when these are not provided in stabilized form. However, there is little direct experimental evidence for harmful effects arising from the use of fats, or fat-containing ingredients, within the range of oxidation likely to be encountered in commercial samples and in well-balanced rations prepared with the precautions now available to the compounder. Practical people, nevertheless, have the impression from field observations that poor results are often seen with rations containing unsaturated fat that have been stored for prolonged periods .In a previous paper (Carpenter, Lea & Parr, 1963) we have reported the last of a series of experiments with herring meal (containing approximately 17 % lipid, that is, the chloroform-methanol extract), which had been allowed to oxidize during storage before it was given at a level of about 18 % to chicks. There was no evidence in these short-term experiments with generous vitamin supplementation of any direct toxic effect of the oxidized fish oil; the slight depressing effect on weight increase observed with the stored, compared with the fresh, meal accompanied the non-lipid rather than the lipid fraction on separation. Small losses of available lysine had previously been shown to result from an interaction between the protein and lipid oxidation products in stored herring meals (Lea, Parr & Carpenter, 1958, 1960. Moreover, addition to the chicks' diet of 2-5 yo of herring oil pre-oxidized to a peroxide value of 142 ,umoles/g available at https://www.cambridge.org/core/terms. https://doi

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A new analytical procedure, determining oxidation products of polyenoic fatty acids, is applied to both fresh and stored foods and fats. The extent of deterioration of the extracted lipid is measured by changes in the ultraviolet spectrum resulting from the chemical reaction steps of the assay-the results are compared with the traditional peroxide value. In the assay not only hydroperoxides of polyenoic fatty acids but also hydroxy and carbonyl compounds derived from them, yield 'conjugable oxidation products' which are measured together and expressed as the 'C.O.P. value'. At the same time an 'oxodiene value' independently determines the unsaturated carbonyl compounds. Another feature of the assay is that is distinguishes between the oxidation products derived from dienoic fatty acids and those of more highly unsaturated polyenoic fatty acids and this is measured by the 'C.O.P. ratio'.For possible greater convenience in quality control, a quicker procedure is also described in which only the final spectrum derived from the conjugable oxidation products is measured.

I. Turkey poults were fed from day-old to 6 weeks on a practical-type diet containing 10% white fish meal (supplying 0 7 % lipid) and other constituents, mainly cereals (supplying 3.3 yo lipid), together with either I ' j % of anchovy oil that had been allowed to autoxidize under various conditions or I' j yo of fresh beef fat. 2. For group I the whole diet with anchovy oil was stored in air at I jo for 3 months before feeding. Its lipid oxidized only slowly, with no appreciable rise in peroxide value and little destruction of its polyunsaturated fatty acids. For groups 2 and 3 the anchovy oil was mixed with the white fish meal, and the mixture was stored for 3 months, by which time most of its polyunsaturated fatty acids had been destroyed by autoxidation and the pv of the extractable lipid, after reaching a peak of 260 ,umoles/g, had fallen again to 110. At this point the anchovy oil-fish meal premixture was further mixed with the basal diet and used, either immediately (group 2) or after 3 months' further storage (group 3). 3. The turkeys in all three groups receiving 'fish oil' remained healthy and grew well, with only slightly apparent (and not significantly) lower weight gains than those on the control diet. There was no significant treatment effect on liver weight, serum aspartate aminotransferase or serum alanine aminotransferase activity. All the birds stored vitamin A in their livers, though the diets had provided not more than adequate supplies of this vitamin, but the reserves accumulated were significantly lower when the diets contained oxidized fat. On roasting, the turkeys of group I had a definite and objectionable fishy flavour, whereas those of groups 2 and 3 were as palatable as the controls on the beef fat diet.

Measurements of oxygen absorption have been carried out on a sample of crude leaf protein, containing about 20% lipid, at temperatures between 37' and -1 2 ' and pH 26-6.0.An enzyme system was active in the moist but not in the freeze-dried product. Attempts to protect the lipid of the freeze-dried protein by the addition of antioxidants were unsuccessful.