EFFECT OF CHEMICAL-STRUCTURE OF FATS UPON THEIR APPARENT DIGESTIBLE ENERGY VALUE WHEN GIVEN TO YOUNG-PIGS

The effect of degree of saturation (ratio of unsaturated to saturated fatty acids, U/S) and free fatty acid (FFA) content of fats upon their digestible energy (DE) values was investigated in post-weaning pigs. The two fats evaluated were soya-bean oil (SO) and tallow (T) (represe nting extremes of saturation) together with their acid oils (SAO and T AO respectively) providing high FFA levels). Blends of the four fats p rovided treatments with varying FFA content and U/S ratios. The experi mental fats were evaluated by substitution, at 40, 80 and 120 g/kg int o a basal diet, in a randomized-block design, with 98 gilts and 98 boa rs of approximately 12 kg live weight. Pigs had been weaned at 28 days of age and experimental diets were given 7 days after weaning. When p igs obtained a weight of 10 kg the inert marker titanium dioxide was a dded to the diets as a reference substance. A 5-day adjustment period was allowed followed by a 5-day collection period of faeces by grab sa mpling. Fat content of food and faeces, with methodology based on acid hydrolysis, allowed calculation of apparent digestible fat (AFD) of e xperimental diets. Analysis of variance demonstrated effects of fats, rates of inclusion, and fats X rates (P < 0.001 in all cases). There w as no effect of sex. Extrapolation of the function obtained by regress ing AFD of diets (y) on rate of inclusion of fat (x) to x = 1000 gener ated values for the fats. The product of the coefficient of fat appare nt digestibility of fats and their respective gross energies gave DE v alues for fats which were: SO = 37.2 MJ/kg, SAO = 35.0 MJ/kg, T = 34.3 MJ/kg and TAO = 27.4 MJ/kg. Data for fat blends intermediary between these fats showed that DE improved as a function of U/S and that DE de clined linearly with increasing FFA content.