A growing-finishing diet formulated to reduce the soybean meal does not compromise the growth performance, health, behaviour and gut health of Italian heavy pigs

Soy contributes to the environmental impact of Italian pork production. This study aimed to evaluate the effect of a reduced soybean meal (SBM) and crude protein (CP) finishing diet on growth performance, health, behaviour and gut health of Italian heavy pigs. 1920 pigs (35.6 kg body weight; (BW)) balanced by sex and BW were assigned to the control diet (CO), or the treated diet (TRT) formulated by reducing SBM by 31%, 67% and 69% (replaced by pea and sunflower meal) in 3 feeding phases, respectively, and 1.2% CP in the third phase. 251 pigs were individually weighed at d11, d94 and d181. Feed intake (FI), behavioural indices and air gases at pen-level were monitored monthly. Faecal samples (20/pigs/group) for microbiota, ammonia and volatile fatty acids (VFAs) and hair for stress biomarkers were collected. Diet did not affect final BW, faecal ammonia, cortisol and dehydroepiandrosterone. From d11–d94, the CO group had higher gain to feed (G:F) (p =.007), favourable faecal VFAs profile and a lower environmental ammonia (p <.0001). From d10–d181, the TRT diet increased the ADG (p =.04) and G:F (p =.01), reduced FI (p <.0001) and the lesions score index at d102 (p =.03) and promoted Methanobrevibacter (d94; padj. = 0.013) and Clostridium sensu stricto (d181; padj. = 0.001). Overall, the TRT diet combined with the stress of the transport and acclimatisation to the farm may limit the growth of pigs in the initial period, but it can increase their growth in the long term. Concluding, replacing 56% of SBM with sustainable alternatives seems promising for heavy pig.