Studies on pig diets containing different amounts of linoleic acid.

Since the deficiency syndrome caused by lack of essential fatty acids (EFA) was first described by Burr & Burr (1929) many species besides rats have been shown to require EFA, but evidence about the pig is rather sparse and conflicting. Ellis & Isbell (1926) and Ellis & Zeller (1930) reared pigs on diets containing only 0 . 5 7 ~ 'ether extract', but observed none of the classical signs of EFA deficiency. Witz & Beeson (1951) studied diets containing 0.06 % fat and noted that their pigs had a reduced rate of weight increase and suffered from dermatitis, necrosis of the skin and loss of hair. Hill, Warmanen, Hayes & Holman (1957) found a high mortality in miniature pigs reared on diets low in fat, but observed no skin lesions. Deuel (1957) considered the pig to represent a species relatively refractory to EFA deficiency. I n EFA deficiency, the content of trienoic acid in tissue lipids rises (Nunn & SmedleyMacLean, 1938). This observation has been confirmed in the rat (Rieckehoff, Holman & Burr, 1949), and has been noted also in the dog (Wiese, Hansen & Baugham, 1957), the chick (Reiser, 1951) and the pig (Leat, 1961 a), but not in the guinea-pig (Reid & Martin, 1959). Holman (1960) has used this metabolic lesion as a basis for estimating the degree of EFA deficiency and has suggested that the ratio, trienoic: tetraenoic acids can be an index of EFA requirement in rats. This trienoic acid formed in EFA deficiency has been identified as an eicosatrienoic acid derived from oleic acid (Mead & Slaton, 1956; Fulco & Mead, 1959). The experiments reported below arose from observations on pigs reared on diets low in tocopherol and EFA. The object was to investigate the fatty acid composition of pigs reared on diets containing various amounts of linoleic acid, and also to test whether the trienoic: tetraenoic acid ratio was as suitable for estimating EFA status in the pig as in the rat. Recently Hill, Warmanen, Silbernick & Holman (1961) have shown it to be so for miniature pigs. Preliminary accounts of the work here reported have been published (Leat, 1959, 1961 a, b).