Abstract
Reducing dietary crude protein (CP) beyond a certain threshold leads to poor growth performance in pigs; however, the underlying mechanisms are not well understood. Following an adaption period, thirty-seven weaned pigs were weight matched (8.41 ± 0.14 kg), housed individually and randomly assigned into three groups with different dietary CP levels: 24% CP (CON; n = 12), 18% CP (n = 12) and 12% CP (n = 13) for 28 days. The body weight was not different between the CON and 18% CP diets, but 12% CP significantly decreased body weight after day 21. Compared to the CON, pigs fed with 12% CP decreased feed intake day 17 onwards. The 12% CP diet increased the energy expenditure during week 1 compared to the CON. The 12% CP influenced starch and sucrose, nitrogen, and branched-chain amino acids metabolism pathways. The feces of pigs fed with 12% CP were less enriched in Prevotella, but had higher relative abundance of Christensenedilaceae, Aligiphilus and Algoriphagus than CON and 18% CP. Overall, reducing dietary CP by 50%, but not by 25%, significantly influenced the physiological responses in nursery pigs. The pigs fed with low or standard protein diets had differential bacterial communities in their feces as well as serum metabolomics profile.
Highlights
Consistent with data from rodent studies[16,17,18,19,20,21,22] and the protein leverage hypothesis stating that several animal species give priority to meet their protein needs over other dietary components[23], severe reduction in dietary protein increases the feed intake as well as heat production in young pigs[24,25,26]
The cumulative weekly feed intake for 12% crude protein (CP) was significantly lower than CON and 18% CP on week 3 (P < 0.011; Supplementary Fig. S1A)
The increased EE together with decreased feed intake contributed to reduced growth performance of pigs fed with moderately low protein diets, 2) decreasing the dietary CP by 50% (i.e. 12% CP) influenced the metabolism of branched-chain amino acids (BCAA), metabolites of amino acids, nitrogen and protein, lipids and vitamins metabolites, carbohydrates and microbiome metabolites, 3) pigs fed with moderately low protein diets had higher abundance of Christensenedilaceae, Algoriphagus and Algiphilus and lower abundance of Prevotella in their feces compared to those fed with slightly low protein or control diets
Summary
Consistent with data from rodent studies[16,17,18,19,20,21,22] and the protein leverage hypothesis stating that several animal species give priority to meet their protein needs over other dietary components[23], severe reduction in dietary protein increases the feed intake as well as heat production in young pigs[24,25,26]. In support of these studies, others[25] reported an increased feed intake and EE in growing pigs fed with extremely low protein diets (2.38% CP) In these studies, www.nature.com/scientificreports limited numbers of pigs were used to assess the effect of dietary protein level on energy balance. Unlike severe reduction in dietary protein, moderately low protein diets (12–15% CP) supplemented with essential amino acids either had no effect[28,29] or decreased the EE in growing and finishing pigs[10,30,31]. While the impact of age on the composition of gut microbiome in pigs is well documented[37], the effect of moderately low protein diets (10–13% CP) supplemented with essential amino acids on intestinal microbiota has been only assessed in finishing and growing pigs[38,39]. The objective of this study was to determine the effect of low protein-high carbohydrates diets on energy balance, blood metabolomics profile and fecal microbiota composition in weaned pigs
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