Prediction of gut capacity of weaner and finishing pigs using physicochemical measurements of bulkiness of fibrous feeds.
Physicochemical properties of different fibrous ingredients were used to determine the influence of feed bulk on voluntary feed intake and gut capacity in weaner and finishing pigs. Physicochemical measures of bulkiness determined on feed ingredients were DM, crude protein (CP), ether extract, ash, water holding capacity (WHC), bulk density, crude fibre (CF), neutral detergent fibre (NDF) and acid detergent fibre (ADF). Among the fibre sources, maize stover had the highest WHC, followed by veld grass, then lucerne hay, maize cob, sunflower husks, groundnut haulms, rice bran and saw dust. The greatest bulk densities (1.4 g DM/ml) were observed in lucerne hay and saw dust, whilst sunflower husk had the lowest (0.7 g DM/ml) (P < 0.001). Rice bran, maize cob and groundnut haulms were the most fermentable fibrous ingredients (P < 0.05). Based on differences in physicochemical properties, six fibres namely lucerne hay, maize cob, maize stover, veld grass, saw dust and sunflower husk were selected and used in formulating fibrous diets fed to growing pigs based on wideness in ranges of their bulk properties. Thirty-one complete diets were formulated by dilution of a conventional weaner feed with increment levels of each fibre source at 0, 80, 160, 240, 320 and 400 g/kg. Each of the diets was offered ad libitum to four of 124 pigs weighing 18.1 (s.d. 1.37) kg body weight, in individual pens, for four weeks. There was a linear decrease in scaled feed intake (SFI) (P < 0.001) as bulk density of the feeds increased. There was a quadratic relationship between SFI and WHC, NDF and ADF, respectively, whereby SFI increased up to a point when it reached its maximum and then started to decrease as bulkiness increased (P < 0.001). By use of the broken stick model, the maximum SFI marking the gut capacity of pigs was attained when WHC = 4.5 ± 1.25 g water/g DM (P< 0.001), NDF = 367 ± 29 g/kg DM (P < 0.001) and ADF = 138 ± 77 g/kg DM (P < 0.01), respectively. The SFI decreased linearly with an increase in bulk density of the feeds (P < 0.001). Four of 84 finishing pigs in individual pens, at 65 (s.d. 1.37) kg body weight were given, ad libitum to each of 21 diets containing graded levels of lucerne, maize cobs, saw dust and sunflower husk. There was a linear decrease in SFI (P < 0.001) as WHC increased. There was a quadratic decrease in SFI as CF (P < 0.001) and NDF (P < 0.01) increased. As CP increased, there was a quadratic increase in SFI (P < 0.01). In weaner pigs, an increase in WHC, NDF, ADF and bulk density constrains feed intake, thereby providing relationships that can be used to predict gut capacity. Conversely, measurements of feed bulk cannot provide relationships with intake that can be used to predict gut capacity in finishing pigs.