A Very Low CP Level Reduced Diarrhoea and Productivity in Weaner Pigs, but No Differences between Post-Weaning Diets Including Soybean Meal or Soy Protein Concentrate Were Found

SIMPLE SUMMARY: Diarrhoea is a challenge after weaning in pigs, and medicinal zinc oxide has been used to decrease this problem. Additionally, soy protein concentrate improves protein digestion and thereby increases growth compared to soybean meal. The aim was to test the effect of different low-protein diets on diarrhoea and productivity. This study demonstrates that a diet with very low-protein levels supplemented with amino acids decreases diarrhoea similar to zinc oxide, but also limits growth performance. Moreover, the study found no effect of low-protein diets with different protein sources. Based on these results, there is potential in feeding extremely low-protein diets to weaned pigs as a tool to decrease diarrhoea and thereby antibiotics usage. Additionally, this study presents an opportunity to use both soy protein concentrate and soybean meal as the main protein source, without affecting pig health and productivity. ABSTRACT: Soy protein concentrate improves nutrient utilization and growth performance compared to soybean meal, and diets with a low crude protein (CP) level decreases diarrhoea. The objectives were to (1) test a low CP diet based on different soy products, and (2) to test a very-low CP diet (15.1%) with amino acids (AA) on diarrhoea and productivity. A total of 5,635 weaned pigs (~28 days), were assigned to five dietary treatments; PC (positive control): Standard CP levels (192, 189, 191 g/kg CP) with 2500 ppm ZnO; NC (negative control): Same as PC without ZnO; SP (Soy protein concentrate): Low CP levels (176, 174, 191 g/kg CP); SB (Soybean meal): Low CP levels (177, 176, 191 g/kg CP); and XLA (X-low CP + AA): Very low CP levels (154, 151, 191 g/kg CP) with AA. The PC and XLA diets reduced diarrhoea by 41 and 61%, respectively, compared to the NC group, while no difference between SB and SP were observed. The XLA diet reduced feed intake and daily gain compared with PC and NC, where SP, SB, and XLA had a poorer feed conversion compared with PC. Conclusively, the SP and SB low-protein diets did not reduce diarrhoea or growth performance, whereas the XLA diet decreased both diarrhoea and performance.