Digestibility of a nutritionally-balanced cassava (Manihot esculenta Crantz) diet and its effect on growth in young male dogs.

Experiments were carried out to study the digestibility of a cassava (gari) diet and its effect on growth in young male dogs. Three groups of dogs were fed on diets with rice (control), cassava (gari), and rice + cyanide respectively as the carbohydrate source. Each diet contained 130 g crude protein (nitrogen x 6.25)/kg, was supplemented with vitamins and minerals, and was fed for 14 weeks. Variables measured were body-weight gain, bone growth, plasma alkaline phosphatase (EC 3.1.3.1) activity, total serum 3,5,3'-triiodothyronine (T3) and some plasma free amino acids. The apparent digestibilities of dry matter, protein and fat were not significantly different in the three groups, but the digestibility of gari fibre was significantly lower than the digestibility of rice fibre when fed to dogs (P less than 0.05). Proximate analysis of the faeces showed that the group of dogs fed on the gari diet had faeces which had a significantly higher moisture content than the faeces of the other groups (P less than 0.05), and also a significantly higher fibre content (P less than 0.05). There was no significant difference in body-weight gain and bone growth between the control and gari-fed groups of dogs, but these variables were significantly lower in the dogs fed on the rice + cyanide diet (P less than 0.05). At the end of the 14-week experimental period total serum T3 and plasma alkaline phosphatase activity were not significantly different between the control group of dogs and the gari-fed group, but were significantly lower in the rice + cyanide group. Plasma free methionine, leucine, isoleucine and valine concentrations were higher in the rice + cyanide group of dogs than in the control group and the gari group, indicating that these amino acids were accumulating and not being utilized for protein synthesis and growth to the same extent in the rice + cyanide group of dogs as in the other groups. It was concluded that the digestibilities of cassava starch and rice starch were the same in the dog but that rice fibre was more digestible in the dog than cassava fibre. It was also concluded that growth proceeded normally when a balanced gari diet or a balanced rice diet containing 130 g crude protein/kg was fed to dogs, but growth was retarded when a balanced rice + cyanide diet containing 130 g crude protein/kg was fed to dogs because total serum T3 concentration became greatly depressed.