No abstract

Introduction  Feedstuffs with elevated contents of bacterially fermentable substrates (BFS: GFE 1987) offered to pigs have intermediate metabolizable energy (ME) contents compared with feedstuffs mainly composed of starch or hardly fermentable fibre (H adorn et al. 1996a,b). Consequently, BFS‐elevated feeds could be used as major components enabling pig fattening rations to obtain the ME values required for feed calculation from tabulated values (DLG 1991) or equations based on nutrient composition (GFE 1996). The main field of application for BFS‐elevated feeds is, however, still the feeding of adult, non‐lactating sows, with the majority of investigations on fermentation characteristics also being conducted with sows. In fattening pigs a higher accuracy of estimated ME contents is required than in non‐lactating sows. Furthermore, the ME values of feeds with elevated BFS contents might be systematically different in sows and fattening pigs because a still incomplete evolution of the fermentative capacity of the hindgut of growing pigs cannot be totally excluded (J entsch et al. 1990). The efficiency of hindgut bacterial protein synthesis might also be different from that being assumed from sow data (e.g. K irchgessner et al. 1989, 1994). The objective of the present study was to determine the actual ME and BFS contents of rations varying widely in type and level of BFS in three experiments with growing pigs. By comparing these values with those calculated from equations or from tabulated values a re‐examination of the currently applied feed evaluation system should be carried out. Furthermore, interactions of BFS with dietary protein reduction were investigated, since in low‐protein rations fermentation efficiency might be limited by a lack of nitrogen in the hindgut (M osenthin 1987).

Knowledge is limited on the efficacy of hindgut-fermentable dietary fibre to reduce blood, bile and body tissue cholesterol levels. In three experiments with growing pigs the effects of different kinds and levels of bacterially fermentable fibre (BFS) on cholesterol metabolism were examined. Various diets calculated to have similar contents of metabolizable energy were supplied for complete fattening periods. In the first experiment, a stepwise increase from 12 to 20% BFS was performed by supplementing diets with fermentable fibre from sugar beet pulp (modelling hemicelluloses and pectin). Beet pulp, rye bran (modelling cellulose) and citrus pulp (pectin) were offered either independently or in a mixture in the second experiment. These diets were opposed to rations characterized in carbohydrate type by starch either mostly non-resistant (cassava) or partly resistant (maize) to small intestinal digestion. The third experiment was planned to explore the interactions of BFS from citrus pulp with fat either through additional coconut oil/palm kernel oil blend or full-fat soybeans. In all experiments the increase of the BFS content was associated with a constant (cellulose) or decreasing (hemicelluloses, pectin) dietary proportion of non-digestible fibre. In experiment 1 an inverse dose-response relationship between BFS content and cholesterol in blood serum and adipose tissue as well as bile acid concentration in bile was noted while muscle cholesterol did not respond. In experiment 2 the ingredients characterized by cellulose and hemicelluloses/pectin reduced cholesterol-related traits relative to the low-BFS-high-starch controls whereas, except in adipose tissue cholesterol content, the pectinous ingredient had the opposite effect. However, the changes in serum cholesterol mainly affected HDL and not LDL cholesterol. Adipose tissue cholesterol also was slightly lower with partly resistant starch compared to non-resistant starch in the diet. Experiment 3 showed that the use of citrus pulp increased serum cholesterol concentrations when levels were low in the corresponding low-BFS diets (low-fat and soy bean diets), but caused no further increase in the coconut-oil/palm kernel oil blend diet. From the present results it seems that fermentable hemicelluloses have a more favourable effect of decreasing metabolic cholesterol and related traits than hardly digestible fibre, fermentable cellulose or, particularly, pectin. Furthermore, some types of fibre expressed a certain potential to reduce cholesterol content of fat pork and pork products by up to 10% (experiment 1) and 25% (experiment 2).