CONTRIBUTION OF OLIGOSACCHARIDE AND POLYSACCHARIDE DIGESTION, AND EXCRETA LOSSES OF LACTIC-ACID AND SHORT-CHAIN FATTY-ACIDS, TO DIETARY METABOLIZABLE ENERGY VALUES IN BROILER-CHICKENS AND ADULT COCKERELS

1. Two experiments were conducted, using both adult cockerels from a layer strain and 3-week-old broiler chickens. In the first experiment, one of the 2 diets investigated was composed mainly of maize and soyabean meals, the other one containing the latter ingredients diluted with 475 g/kg mature pea seeds. For these 2 diets, the apparent metabolisable energy values corrected to 0 nitrogen retention (AME(n)) were derived, together with the apparent digestibilities of nitrogen, amino acids, total lipids, starch, individual oligosaccharides, and non-starch polysaccharides (NSP). Excretions of lactic acid and short chain fatty acids (SCFA) were also determined. 2. In the first experiment, the mean apparent digestibilities of starch, lipids, total amino acids, NSP, sucrose and alpha-galacto-oligosaccharides in adult cockerels were 0.946, 0.785, 0.835, 0.045, 0.99 and 0.99, respectively. In broiler chickens, they were 0.938, 0.675, 0.830, -0.016, 0.988 and 0.867, respectively. The bird type effects were significant (P < 0.05) for the digestibilities of starch, lipids, NSP (for the maize-soyabean meal diet, only) and alpha-galacto-oligosaccharides. Broiler chickens excreted a mean of 11.032 g organic acids/kg diet against 4.190 in adult cockerels (P < 0.001). These digestibility measurements enabled the contribution made by each dietary component to the AME(n) value of the diets to be calculated. AME(n) values were lower in broiler chickens than in adult cockerels, with on average 0.8 MJ/kg dry matter difference resulting from bird type. This difference was accounted for by differences between bird types in energy supplied by lipids (34.0%), starch (7.5%), alpha-galacto-oligosaccharides (8.7%), NSP (14.2%), and in energy losses from lactic acid excretion (16.4% of the difference in AME(n) between bird types). 3. In the second experiment 2 diets were studied, consisting of a basal and the basal diluted with 30 g/kg lactose (a fermentable sugar in chickens) and 12 g/kg of a water-soluble gel-forming component containing 50% polygalacturonic acids. Lactose digestibilities reached 0.928 and 0.712 in adult cockerels and chickens, respectively. The digestibilities of the water-soluble polygalacturonic acids were similar in cockerels and broiler chickens, with a mean value of 0.672. Figures similar to those of the first experiment were found in the comparison between cockerels and broiler chickens, for the AME(n) values of diets, the digestibilities of starch and lipids and the excretion of lactic acid. Broiler chickens excreted 4.580 g lactic acid/kg dry food intake, compared with 0.740 g in the adult. Additions of lactose and polygalacturonic acids resulted in significant increases in excreta losses of lactic acid and SCFA. The latter increases in organic acid losses amounted to 0.024 and 0.049 g/g of the digested fraction of (lactose + galacturonic acids) in adult cockerels and broiler chickens, respectively.