Evaluating the effects of a low-protein diet with reduced amylose-amylopectin ratio in fattening pigs on performance, gut health and behaviour

Reducing dietary crude protein (CP) and using synthetic amino acids (AAs) reduces environmental impact but may affect pigs' growth. This study aims to evaluate the effect of a low CP and a low amylose-to-amylopectin ratio (AM:AP) diet on performance, welfare, and faecal microbiota of growing-finishing pigs. 384 pigs (36.76 kg) were assigned to a control (CO) or a treated (TRT) diets blocked for sex and body weight. The TRT reduced the CP by 1.5%, 1.4%, and 0.7% across three feeding phases and the AM:AP ratio (TRT = 7 vs CO = 16.97). Pigs were weighed at day (d) 0, d36 and d160; faecal samples (16 pigs/group) were analysed for microbiota (v3-v4 16S rRNA gene sequencing), calprotectin, volatile fatty acids (VFAs) and ammonia concentrations at d11, d36 and d160. Behavioural indices and pen-level air gases were monitored monthly. No differences in performance were observed. Faecal microbiota alpha diversity was affected by diet-time interaction (p < 0.0001). At d36 and d160, the TRT had a higher abundance of Clostridium sensu stricto 1 (p = 0.002, p = 0.009, respectively) and Terrisporobacter (p = 0.03, p = 0.02, respectively). Total VFAs and butyric acid at d11 and iso-butyric and iso-valeric acids at d161 were higher in the males of the TRT group (p < 0.05). On d71, the TRT group had a higher environmental carbon dioxide (p < 0.02) concentration. TRT pigs exhibited greater activity (p = 0.03 at d50), with no differences in tail or ear lesions. In conclusion, a low CP and AM:AP diet can maintain fattening pigs performance and welfare while indirectly potentially reducing environmental impact.