Abstract
A bioassay technique was developed for the determination of biologically available energy of various fats and oils, based on the response of day-old chicks to the dietary nutrients. The assay technique was already used for the determination of available energy of sweet potato4), which was refined and modified to be suitable especially for fats and oils.
Body weight gain of chicks can be shown as functions of dietary energy and protein levels under a certain conditions3). When dietary protein level is kept constant, curve-linear relation will be obtained between chick's gain (y) and dietary energy level (x2), which may be approximately linear within a certain narrow range of dietary energy level as described by Equation 3, where a and b are constants. Several other conditions
y=a+bx2 (3)
should be satisfied to obtain the linear relationship, such as that dietary protein level should be kept constant, that dietary vitamins and minerals should be enough and so on.
With the linear equation obtained with standard diets of various energy levels, the energy level of unknown diet will be estimated from the y of chicks fed the diet. This is the fundamental principle of the new bioassay technique. From the previous data, it was suggested that the linear equation could be obtained with dietary protein level of 23% and dietary energy level, shown as percent of total digestible nutrients, between 60% and 76%.
The basal diet contained 10% of cornstarch, which was replaced by various levels of soybean oil in the standard diets and of test material in the test diets, while keeping the other 90% of ingredients constant. Therefore, all experimental diets contained the same amount of crude protein, i.e. 23%, and of minor nutrients, such as vitamins and minerals, with the various levels of energy.
The results obtained in Expt. 502 revealed that Equation 6 was suitable to describe the relationship, which was given in Fig. 1. Fiducial limit of the estimated energy was discussed and given by dotted line in Fig. 1.
Total digestible nutrients (TDN) were used in these experiment as unit of energy, because TDN is commonly used in this country. Since available energy estimated by this assay is a kind of net energy in nature, TDN is not the best unit of energy in this case. However, Equation 3 may be satisfactory regardless to the unit, so that available energy estimated by this assay can be given by any unit, if the energy contents of cornstarch and soybean oil be expressed by the unit.
Corn fermentation oil, which was the residue of alcohol fermentation, was determined to be 186% of TDN. True digestibility of this oil was 86.6% with standard deviation of 3.7%, so that TDN was calculated to be 195±8.3%. It is clear that two values of corn fermentation oil determined by two different methods were quite agreeable within the experimental error.
