Abstract
Fatty acid of sperm whale oil (SWO), usually in the form of sodium soap, was obtained by the saponification of SWO to separate the higher alcohol and hitherto used by the soap industry. Free fatty acid of SWO had the melting point of 19-20°C and gross energy of 9.34kcal/g, determined by the bomb calorimeter. This may be one of the fat sources of poultry feed which is very limited in this country.
In this paper, available energy of free fatty acid of SWO, its methyl ester, calcium and sodium salts was determined biologically based on the body weight gain of White Leghorn male chicks for 4 or 8 weeks as described in the previous papers8). In each experiments, standard diets containing cornstarch or soybean oil or the mixture of them were fed to chicks to obtain the standard curve. In this paper, the available energy was given as percentage of total digestible nutrients (TDN), since this is common in Japan.
Available energy of free fatty acid of SWO was 173% of TDN with 95% fiducial limit of ±15%, which was comparable to that of fancy tallow13). Available energy of methyl ester of SWO fatty acid was 137% and that of Ca-salt was 95% with fiducial limit of ±19%, which was determined biologically with diet containing 10% of Ca-salt, dietary Ca level being adjusted carefully. Sodium salt of SWO fatty acid had growth retarding effect, although only 2.5% of the salt was added in the test diet, and dietary Na level was adjusted by subtracting NaCl.
Although it was reported in the literature that the digestibility of free fatty acid was lower than that of corresponding glyceride, true digestibility of free fatty acid of SWO and its methyl ester was as high as 92-95%, which was comparable with digestibility of soybean oil, 97%. However, the growth rate of chicks fed fatty acid of SWO was slower than that of chicks fed soybean oil, while relatively little difference in feed intake, therefore in fatty acid intake, in digestibility of fatty acid, and in the amount of carcass fat accumulated, was observed between two groups of chicks. Caloric value of SWO fatty acid and soybean oil was similar, being 9.34 and 9.39kcal/g, respectively. Therefore, it was supposed that part of digested fatty acid of SWO was not utilized by chicks and lost as heat.
Calcium salt of SWO fatty acid with small amount of sodium used in the saponification of SWO was found to have nutritive value comparable with free fatty acid of SWO and beef tallow, when fed at the level of 2%. On the practical view point, it may be most reasonable to use Ca-salt of this type, with dietary level of about 2%.
