Animal wastes. II. Chemical and nutritional evaluation of by-products from rennet and proteases production.
Drum-dried calf stomach waste (DDSW) from rennet production, after washing with water for salt elimination, as well as drum-dried porcine pancreas waste (DDPW) from protease extraction were used. Their chemical composition and nutritional values were studied. The protein content of DDPW was two-thirds that of the DDSW sample. The amount of ashes (acid soluble and insoluble) in DDPW was twice that of DDSW. Four diets, the protein sources of which were casein, DDSW, DDPW and a mixture of equal parts of both by-products (MSPW) were then prepared. Their nutritive value was assessed in weanling rats through the following parameters: food ingestion, body weight gain, protein efficiency ratio (PER) and and apparent protein digestibility. The DDSW sample showed the lowest nutritional quality for all parameters measured. The weight gain of rats fed diets containing casein, DDPW, MSPW, and DDSW were, 59.60 +/- 8.12, 84.63 +/- 9.89, 56.22 +/- 6.74, and 20.08 +/- 3.72, respectively. The PER for the same diets were: 2.82 +/- 0.33, 2.67 +/- 0.19, 2.17 +/- 0.25, and 1.30 +/- 0.20, in the same order. The protein digestibility of all experimental diets was about 70%, and that of the control diets, about 90%. As a conclusion, the by-product of protease production from porcine pancreas seems adequate as a protein source for animal feeding, despite its high level of ashes. Also, this by-product appears to be useful for feeding purposes, when mixed with the other animal by-products studies.