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Two experiments were conducted to test the following hypotheses: (1) decreasing particle size of lupins will increase total-tract apparent protein digestibility irrespective of lupin variety; (2) decreasing particle size of lupins will increase apparent ileal digestible AA content linearly in growing pigs within the range of particle sizes seen commercially (600–1300 µm); (3) decreasing particle size of lupins will decrease the amount of N entering into the large intestine and in turn decrease indices of protein fermentation such as NH3 and BCFA.
Expt 1 examined the effects of lupin variety (Tanjil and Mandelup) and lupin particle size (746, 888, 1099 and 1136 µm) on the total-tract apparent digestibility of dietary components in 63.5 (SD 7.28) kg pigs. While variety had no effect on total-tract apparent digestibility, decreasing particle size of lupins linearly increased total-tract apparent digestibility of crude protein of diets containing 350 g lupins per kg (P<0.01). Expt 2 examined the effect of lupin particle size (567, 995, 1198, 1250 and 1304 µm) on digestion and fermentation characteristics in 29.8 (SD 2.9) kg pigs. Pigs were fed the respective diets ad libitum for the first 2 weeks and fed at three times maintenance energy level in the third week. Pigs were euthanised under sedation at 46.7 (SD 4.21) kg to collect digesta samples along the intestinal tract. Decreasing particle size increased apparent ileal and total-tract digestible N (P<0.01) and the apparent and standardised ileal digestible AA content (P<0.05–<0.001) of lupins. Decreasing particle size of lupins linearly decreased the molar proportion of straight-chain volatile fatty acids (sum of acetic, propionic and butyric acids; VFAAPB), while branched-chain fatty acids (sum of valeric, caproic, isobutyric and isovaleric acids) were linearly increased (P<0.001).
It is concluded that particle size of lupins is a critical factor influencing nutrient, especially AA, utilisation efficiency and fermentation characteristics in the gastrointestinal tract of pigs.
JC Kim, BP Mullan, JM Heo, CF Hansen and JR Pluske. 2009. British Journal of Nutrition. 102:350-360.
