Biological assay technique was applied for the determination of available energy of cassava meal, which was imported from Thailand for the first trial. Standard curve was obtained with the growth rate of chicks fed standard diets of various energy levels. Corn starch and yellow corn in the standard diet was replaced with cassava meal and levels of soybean oil and fish weal were adjusted to set the dietary energy and protein levels. With the growth rate of chicks on diet containing cassava meal, available energy of cassava meal was calculated with electronic computer. The available energy was shown as percentage of total digestible nutrients as in the previous 3 papers^{2, 3, 11)}.
In Expt. 411, it was shown that cassava meal fed at the level of 32.3% had growth retarding effect to day-old White Leghorn chicks, although no chick died during the experimental period of 4 weeks. In Expt. 503, cassava meal was soaked in water overnight or autoclaved at 120°C. for 1 hour. These treatments were quite effective to improve the growth rate of chicks. Diets containing 10 and 20% raw cassava meal were also fed in this experiment and it was revealed that chicks on 10% cassava diet grew almost satisfactorily, but the growth rate of chicks on 20% cassava diet was much slower than expected. To confirm the observation, diets containing 10 and 15% raw cassava meal was fed to 4-week-old chicks in Expt. 505. The growth rate of chicks on 10% cassava diet was normal but that on 15% cassava diet was not.
It was revealed in these experiments that cassava meal had some growth inhibiting factor which will be removed by heat-treatment or water-soaking. The growth-retarding effect was not detected when cassava meal was fed at 10% level. Prussic acid in cassava mael was discussed as the most possible growth-retarding factor. Available energy of cassava meal, when fed at 10% level or autoclaved or soaked in water was estimated. 70% in average. It is ecommended to use cassava meal at the level of less than 10% in poultry feed.
P.S. after the preparation of the manuscript, the authors have received the reprints of papers of Dr. Vogt et al, ^{20, 21, 22)} in which it was reported that the growth rate of broiler chicks on the diet containing 10% of cassava meal was normal. The content of prussic acid in their sample²²⁾ was much less than 36ppm in the sample tested in this paper.