EFFECT OF ADDED SOYBEAN OIL AND DIETARY ENERGY ON METABOLIZABLE AND NET ENERGY OF BROILER DIETS

1. The 'extra caloric' effect of added soyabean oil, as reflected in i mproved body weight gain, food utilisation, metabolisable energy or ne t energy deposition in the body was determined. 2. Two diets were form ulated to contain 12.1 MJ/kg, one with no added fat and the second wit h 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 tota l 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 soyabea n oil increased the apparent digestibility of total dietary fat and re duced that of starch. 3. The effect of soyabean oil supplementation on mash diets at both energy concentrations or to the pelleted diet (for mulated to contain 12.1 MJ) on AME(n) was consistently positive althou gh not significant. Addition of soyabean oil improved net energy depos ition in the body by 17% within the 12.1 MJ/kg diets, (30 g/kg soyabea n 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 pelle ted 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 ad ded soyabean oil, defined as the beneficial effect of the oil above th at 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.