Prediction of voluntary feed intake from physicochemical properties of bulky feeds in finishing pigs

The objective of the current study was to determine the physicochemical properties that can be used to predict scaled feed intake (SFI) in finishing pigs. A total of 84 pigs weighing 65±1.37 kg body weight were given, ad libitum, each of the 21 diets containing a basal feed diluted with 80, 160, 240, 320 and 400 g/kg of lucerne hay, maize cob, sawdust or sunflower husks. Each of the 21 diets was given to four pigs, in individual pens, for 21 days. Physicochemical properties of the feeds measured were dry matter (DM), crude protein (CP; g/kg DM), ether extract (g/kg DM), ash (g/kg DM), water holding capacity (WHC; g water/g DM), bulk density (g DM/ml), crude fibre (CF; g/kg DM), neutral detergent fibre (NDF; g/kg DM) and acid detergent fibre (ADF; g/kg DM). The most important predictors of scaled feed intake (SFI) were NDF (R2=0.76; P<0.05), CF (R2=0.76; P<0.05), CP (R2=0.75; P<0.001) and WHC (R2=0.73; P<0.001). There was a quadratic relationship between SFI and NDF given by the function SFI=82.0 (±5.30)-0.18 (±0.03) NDF+0.0002 (±0.00004) NDF2 (P<0.01). The SFI was related to CF and CP by quadratic functions; SFI=63.4 (±2.22)-0.16 (±0.03) CF+0.0003 (±0.00007) CF2 (P<0.001) and SFI=61.8 (±9.68)-0.39 (±0.16) CP+0.002 (±0.0006) CP2 (P<0.01), respectively. The SFI was related to WHC by linear function; SFI=77.3 (±4.37)-7.43 (±1.77) WHC (P<0.001). It can be concluded that WHC, CF and NDF content provide relationships with SFI in finishing pigs. These physicochemical properties, however, did not provide threshold values that mark breaking points were intake of bulky feeds is reduced due to gut fill.