It was found that chickens absorb unsaturated fatty acids (USFA) more than Saturated fatty acids (SFA),( renner and hill, 196la, and grrett,1963), And that the absorption of SFA was improved in the presenee of USFA. (young. 196l). this was attributed to the formation of emulsions between the USFA and the Bile salts which facilitate the absorption of SFA, (Lewis and payne 1966) The truc Metabo;izable energy (TME) value determined by Sibbald and Kramer (1977) for Rapeseed oil (rich in USFA) and beef tallow (rich in SFA), WERE 9.31 AND 7.00Keal (38.9 and 29.3mj) /g respectively. When two fats were mixed (50:50) the
Two fats mixture was 8.16 Kcal (34.1 MJ) / g. They stated that on mixing the two fats he value of beef tallow increased form 7.00 to 9.00 Kcal (29.3 to 37.6 MJ) g. Also Lall and Slinger (1973) found that ME value of a mixture of rapeseed oil (rich in USFA) and tallow was greater than anticipated from fats fed alone. They reported that This synergism between the two fats was less for turkey than chickens. The same Results were obtained when using a mixture of dalmatic and stearic acids instead of tallow. Sibbald tallow. Sibbald and Kramer (1977) came to the conclusion that the TME value of fat
increased when the cotent of SFA+MUFA was less and the content of dienoic (C18:2) was high, and added that MUFA and trienoiee (18:3) seemed to have no Effect on TME. Sibbald(1978b), found that mixing beef tallow with lard (the two fats Are rich in SFA) gave identical TME as caleulated from the value of cach fat but When mixing beef tallow with soybean oil (rich in USFA) great improvement in the TME of tallow occurred He reasoned that to the low and high contet of (18:2 being 10.2 and 48.6% for lard and SBO respeetively)
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