Effects of rapeseed protein on growth performance, nutrient digestibility, nitrogen balance, serum parameters, and intestinal health of piglets

The global scarcity of high-quality protein resources, such as soy protein concentrate (SPC) and fish meal (FM), highlights the need to develop alternative protein sources. Rapeseed protein (RP) was prepared and its nutritional value was evaluated in piglets in a previous study. However, its effect on the growth and health of piglets remains unclear. Therefore, this study investigated the effects of replacing SPC and FM with RP on the growth and health of piglets. A total of 120 piglets aged 24 to 25 d (7.82 ± 0.42 kg) were randomly assigned to five dietary treatments for a 28-d trial, with 8 replicates per treatment and 3 piglets per replicate. The control group was fed a diet containing 5% SPC and 5% FM. For the 50% SPC replacement group and 100% SPC replacement group, 50% and 100% of the SPC in the diet were replaced with an isonitrogenous amount of rapeseed protein, respectively, with the FM content remaining at 5%. For the 50% FM replacement group and 100% FM replacement group, 50% and 100% of the FM in the diet were replaced with an isonitrogenous amount of rapeseed protein, respectively, with the SPC content maintained at 5%. The results showed that dietary treatments had no effect on the growth performance of piglets (<i>P</i> > 0.05). However, when RP replaced 100% SPC or 50% and 100% FM, there was a significant reduction in the feed-to-gain ratio (<i>P</i> = 0.006). Moreover, piglets fed RP diets had higher crude protein digestibility (CPD) and greater expression of amino acid transport-related genes compared with those fed the control diet (<i>P</i> < 0.05). Furthermore, replacing either SPC or FM with RP promoted the secretion of orexigenic hormones, reduced inflammatory responses, and enhanced both immune function and antioxidant capacity. Additionally, RP replacing SPC or FM increased the expression of genes related to protein synthesis in the longissimus dorsi (mammalian target of rapamycin [<i>mTOR</i>] and phosphorylate 70 ribosomal protein S6 kinase [<i>p70S6K</i>]) and liver (<i>mTOR</i> and protein kinase B [<i>Akt</i>]; <i>P</i> < 0.05), improved the morphology of jejunum and ileum, and enriched the relative abundance of <i>Blautia, Gemmiger,</i> and <i>Haldemanella</i> in colonic digesta (<i>P</i> < 0.05). Overall, the use of RP as a substitute for SPC and FM in piglet diets showed positive effects on growth and development of piglets. However, further investigation into the underlying mechanisms of these effects, as well as an evaluation of the cost-effectiveness of RP production, should be considered.