An investigation into the effect of dietary particle size and pelleting of diets for finishing pigs

• Pelleting and finely grinding diets for finishing pigs improved feed efficiency, average daily gain and nutrient digestibility.
• The effect was cumulative and not interactive.
• Neither pelleting or fine grinding adversely affected the incidence of stomach ulceration in pigs.

The aim of the study was to investigate the effects of feed form (meal or pellets) and dietary particle size profile (fine or coarse) in a 2×2 factorial design on finishing pig performance and nutrient digestibility. A simple cereal soya-based finishing pig diet was formulated to provide 13.6 MJ/kg digestible energy (DE) and 167 g/kg crude protein (CP). The coarsely ground diets were made using 2×14 mm+4×10 mm screens and 6×4 mm screens were used to produce the finely ground diets. Diets were then pelleted or not. The effect of feed form and particle size was tested on pig performance (20 pigs per pen, 8 replicates per treatment) and nutrient digestibility (8 pigs/replicates per treatment) in two separate trials. Data were analysed by Analysis of Variance (ANOVA) using Genstat Version 14.0 according to the 2×2 factorial design. There was no significant interaction (P>0.05) between particle size and feed form. However, the ADG and feed conversion ratio (FCR) of pigs between 18 weeks of age and finish was significantly improved (P<0.05 and<0.001, respectively) when diets were in pellet form (990 g/day and 2.79, respectively) compared with when diets were in meal form (940 g/day and 3.01, respectively). Pigs offered the finely ground diets also had a higher ADG (989 g/day, P<0.05) (between 18 weeks and finish) and a better FCR (2.82, P<0.01) than pigs offered coarsely ground diets (941 g/day and 2.98, respectively). Overall FCR between 12 weeks of age and finish was improved by 5.5% when diets were pelleted (P<0.001) and by 3% when diets were finely ground (P<0.05). Pelleting of the diet significantly improved dry matter (DM) digestibility and DE content (both P<0.05) and tended (P<0.1) to improve energy digestibility and ash digestibility. Reducing the particle size of the diet significantly improved CP digestibility (P<0.05) and tended (P<0.1) to improve DM, energy digestibility and digestible energy content. Nitrogen excretion was reduced (P<0.05) by 10% when pigs were offered diets in pellet form compared to meal form. There was no effect of feed form or particle size (P>0.05) on stomach ulceration. Overall, the results suggest a cumulative effect of feed form and particle size on FCR, nutrient digestibility and DE content of the diet since these parameters were optimized when pigs were offered a pelleted diet with a fine particle size profile but were poorest when meal diets with a coarse particle size profile were offered.