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) (representing extremes of saturation) together with their acid oils (SAO and TAO respectively) providing high FFA levels). Blends of the four fats provided treatments with varying FFA content and U/S ratios. The experimental fats were evaluated by substitution, at 40, 80 and 120 g/kg into a basal diet, in a randomized-block design, with 98 gilts and 98 boars 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 pigs obtained a weight of 10 kg the inert marker titanium dioxide was added 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 sampling. Fat content of food and faeces, with methodology based on acid hydrolysis, allowed calculation of apparent digestible fat (AFD) of experimental diets. Analysis of variance demonstrated effects of fats, rates of inclusion, and fats X rates (P < 0.001 in all cases). There was no effect of sex. Extrapolation of the function obtained by regressing AFD of diets (y) on rate of inclusion of fat (x) to x = 1000 generated values for the fats. The product of the coefficient of fat apparent digestibility of fats and their respective gross energies gave DE values 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 declined linearly with increasing FFA content.