The objective of the present study was to predict scaled feed intake (SFI) using the physico-chemical measurements of feed bulk, such that gut capacity can be estimated in weaner pigs. A basal feed with 13·7 MJ digestible energy and 180 g crude protein per kg DM was diluted to six inclusion levels (0, 80, 160, 240, 320 and 400 g/kg DM) using lucerne hay, maize cob, maize stover, sawdust, sunflower husks or grass hay (veld grass). A total of 124 pigs weighing 18·1 (sd 1·37) kg body weight were used. Water-holding capacity (WHC; g water/g DM), bulk density (g DM/ml), neutral-detergent fibre (NDF) and acid-detergent fibre (ADF) influenced the SFI. The quadratic relationship between SFI and WHC was SFI = 19·1 (sem 3·49)+10·04 (sem 1·61) WHC–1·11 (sem 0·17) WHC2 (P< 0·01). SFI was also related (P< 0·01) to NDF and ADF by quadratic functions SFI = 24·3 (sem 3·55)+0·12 (sem 0·229) NDF − 0·00 012 (sem 0·000036) NDF2 and SFI = 30·2 (sem 1·95)+0·112 (sem 0·0232) ADF–0·000343 (sem 0·0000612) ADF2, respectively. Using broken-stick analyses, the gut capacity was attained when WHC = 4·53 (sem 1·25) g water/g DM, NDF = 367 (sem 29) g/kg DM and ADF = 138 (sem 77) g/kg DM. In conclusion, although threshold values for each were different, WHC, NDF and ADF contents of bulk feeds provide relationships with SFI that can be used to predict gut capacity in weaner pigs.
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