Effect of added soyabean oil and dietary energy on metabolisable and net energy of broiler diets.

1. The 'extra caloric' effect of added soyabean oil, as reflected in improved body weight gain, food utilisation, metabolisable energy or net energy deposition in the body was determined. 2. Two diets were formulated to contain 12.1 MJ/kg, one with no added fat and the second with 30 g/kg soyabean oil. Addition of oil improved body weight gain by 6.9% (P < 0.05). Two other diets were formulated to contain 13.0 MJ/kg, one with 30 and one with 60 g/kg added soyabean oil bringing the total fat in the high energy, high fat diet to 84 g/kg. Addition of oil in this case improved weight gain by only 3.4% (ns). Addition of soyabean oil increased the apparent digestibility of total dietary fat and reduced that of starch. 3. The effect of soyabean oil supplementation on mash diets at both energy concentrations or to the pelleted diet (formulated to contain 12.1 MJ) on AMEn was consistently positive although not significant. Addition of soyabean oil improved net energy deposition in the body by 17% within the 12.1 MJ/kg diets, (30 g/kg soyabean oil addition) (P < 0.05), but was reduced by 2% (ns) within the 13.0 MJ/kg diets (60 g/kg soyabean oil addition). 4. Supplementing a pelleted diet formulated to contain 12.1 MJ/kg, with 30 g/kg soyabean oil, improved food utilisation (P < 0.05). The 'extra caloric' effect of added soyabean oil, defined as the beneficial effect of the oil above that predicted from its energy value, varied according to the parameter chosen to express this effect and was influenced by the concentration of added soyabean oil and the dietary energy.