NUTRIENT APPARENT DIGESTIBILITY AND THE PERFORMANCE OF GROWING FATTENING PIGS AS AFFECTED BY INCREMENTAL ADDITIONS OF FAT TO STARCH OR NONSTARCH POLYSACCHARIDES

In a factorial design, animal fat was added incrementally (0, 35, 70 a nd 105 g/kg) to maize starch (M) or to two sources of fermentable carb ohydrates (260 g purified cellulose (C) per kg or 270 g soya-bean hull s (S) per kg). The 12 experimental diets were formulated by replacing maize starch in the control diet with fat, cellulose and soya-bean hul ls of equivalent estimated net energy. Ninety-six castrated males were given these diets according to net energy. Apparent digestibilities o f crude protein, crude lipid, crude fibre and nitrogen-free extract we re measured and were compared with those expected from the separate in gredients. Net energy conversion ratio (nECR) was also measure. Result s showed that in the C and the S diets prediction of the apparent dige stibility of nutrients was worse than in the M diets (significant effe ct of source of carbohydrate). Prediction of apparent digestibility of crude protein and crude lipid improved as the added fat increased (si gnificant effect of amount of fat), except in the C and S diets where for digestible crude lipid the 70 g added fat per kg gave the worst pr ediction (significant effect of the interaction). The net energy calcu lated from the experimental data on apparent digestibility was proport ionately between 0.83 and 0.98 of that calculated from the expected da ta. The pigs on the C and S treatments showed a significant lower nECR when calculated from the expected apparent digestibility coefficients , but not when calculated from those which were measured. At the highe st fat addition, the nECR was poorest. It is concluded that the amount s of digestible components in compound foods cannot always be obtained from those in the separate ingredients.