Data from experimental programmes designed to investigate the effect of chemical structure of fats upon their apparent digestible energy (DE) value for pigs were subjected to regression analysis. For growing pigs, over the approximate live-weight range 30 to 90 kg, 25 data points were available, with fats evaluated having a range in the ratio of unsaturated to saturated fatty acids (U/S) from 0-66 to 15-67 and in free fatty acid (FFA) content from 8 to 818 g/kg. Sixteen data points were available for young pigs of approximately 12 kg live weight with a range in U/S from 0-62 to 5-71 and in FFA content from 54 to 756 g/kg. The wide range of values for U/S and FFA content had been obtained by blending different fats and, therefore, represented both the range and extremes likely to be found in the formulation of pig diets. Derivation of prediction equations for DE were based upon a series of non-linear regression analyses employing, in sequence, U/S, U/S + FFA content and U/S X FFA content. The DE of fats could be predicted from U/S and FFA content with equations accounting for 0-802 and 0-768 of the variation in DE values for growing and young pigs respectively. The most appropriate equation for pigs of all live weights employed U/S and FFA content additively (U/S + FFA content). The equation for growing pigs was DE (MJ/kg) = 36-898 -(0-0046FFA (g/kg)) -7-33e(-0-906U/S) and for young pigs was DE (MJ/kg) = 37-890 -(0-0051FFA (g/kg)) -8-20e(-0-515U/S). Comparisons revealed that differences between the two age groups, with lower values achieved with younger pigs, -were more pronounced the lower U/S and the higher FFA content of the fat.

Four metabolism trials were conducted. Trials 1 and 2 (Tl, T2) investigated degree of saturation of fats (ratio of unsaturated to saturated fatty acids, U/S) on digestible energy (DE) content. Fats evaluated were rape oil (RO) and tallow (T) for Tl (U/S 15-67 and 0-97 respectively) and RO and palm oil (PO) for T2 (U/S 15-33 and 0-85 respectively). Three fats of intermediary U/S for each trial were produced by blending the two fats in proportions to give U/S of 3-18,2-08 and 1-49 in both trials. Trials 3 and 4 (T3, T4) investigated the effect of free fatty acid (FFA) content of fats on DE value. Fats were soya-bean oil (SO) and soya-bean acid oil (SAO) for T3 (FFA 6-2 and 626-0 g/kg respectively) and T and tallow acid oil (TAO) for T4 (FFA 44-3 and 818-2 g/kg fat respectively). Three fats of intermediary FFA for each trial were formed by blending the two fats in the ratios of 72 :25, 50:50 and 25 : 75 in both trials. The FFA content of the blends were 161-2, 316-1 and 471-1 g/kg fat for T3 and 237-8, 431-3 and 624-7 g/kg fat for T4. All trials evaluated five fats by substitution, at 40, 80 and 120 g/kg into a basal diet, in a cross-over design, with 16 gilts of 25 kg initial live weight evaluating 16 diets over four time periods. Diets were offered for 10 days followed by a 5-day collection period using the marker to marker technique. 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 gave effects of fats (P < 0-001 for Tl, T3 and T4 and P = 0-014 for T2), rates of inclusion (P < 0-001 for all trials), and fats X rates (P > 0-05, P > 0-05, P < 0-001, P < 0-01 for Tl, T2, T3 and T4 respectively). 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 apparent fat digestibility of fats and their respective gross energies gave DE values for fats which were MJ/kg: Tl . Data for fat blends intermediary between the two fats showed that DE improved exponentially as a function of U/S and that DE declined linearly with increasing FFA content.

No abstract

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.