Abstract Low-crude protein (CP) diets have been implemented as a strategy to control post-weaning diarrhea and to reduce the environmental footprint from intensive pig production. However, prolonged feeding of low-CP diets can adversely affect growth performance in nursery pigs because of a lack of synthetic amino acids (AAs) and glucose synchronization. A reduction in the amylose to amylopectin (AM/AP) ratio can improve AAs and glucose synchronization. The objective of this study was to determine the effects of a feeding plan with reduced CP diet in the first phase post-weaning, and reduced CP and reduced AM/AP ratio in the second phase on growth performance, gut microbiota, metabolites, and behavior of weaned pigs. At weaning (28 ± 2 days old), a total of 540 pigs (5.9 ± 0.08 kg) were allocated to 2 groups on first phase diet (d0-d21): CRT= fed a standard diet with medium CP content (16.6%) including 180 piglets (5 pens; 36 piglets/pen) or LCP= low CP diet (14.9%) including 360 piglets (10 pens; 36 piglets/pen); and to 3 groups (5 pens; 36 piglets/pen) on the second phase diet (d22-d63): CTR= continued with a diet with medium CP content (17.2%); LP= fed a low-CP diet (15%) with a high AM/AP ratio (0.17%) and LPLA = fed a low-CP diet (15%) with a low AM/AP ratio (0.08%). No significant difference in growth performance between the CTR and LCP groups was observed in phase I. On d43 and d63, LP and LPLA pigs had lower body weight compared with CTR pigs (P 0.0001), while there were no significant differences in feed to gain (F:G) between CTR and LPLA from d43 to 63. On d21, LCP pigs showed higher fecal dry matter (DM) compared to CTR pigs on d21 (P = 0.011). On d43, the LPLA diet reduced concentrations of fecal uracil compared to the CTR diet (P 0.05). On d63, LPLA pigs were characterized by a greater abundance of Lactobacillus (LDA score = 5.01, P 0.05). The LP diet tended to increase the proportion of enrichment material investigation and increase the lesion score index on the ears compared to the CTR (P 0.10), while no differences were observed between the CTR and LPLA groups. In conclusion, reducing the dietary CP level to approximately 15% during the early post-weaning phase can maintain the growth performance of nursery pigs comparable to that of a 17% CP diet, without AM/AP ratio modulation when diets are supplemented with feed-grade amino acids. Furthermore, during the late post-weaning period, lowering the AM/AP ratio in low-CP diets may provide potential benefits in preventing growth impairments associated with protein restriction and in promoting gut health in nursery pigs.
Lee et al. (Wed,) studied this question.