The influence of dietary concentration of nitrogen and phosphorus on performance and nutrient excretion of growing-finishing pigs, potential genotype by diet interactions and the role of gut microbiome

Abstract

Rising feed costs and a high environmental burden from nutrient excretion need a re-evaluation of feeding and breeding strategies in pig production. Approaches focus on minimizing nitrogen and phosphorus (N/P) excretion, with dietary N/P restriction being well-established in animal nutrition. Studies have shown genetically determined variations in adaptability to such restriction, termed genotype×diet interactions (G×D). The background of these variations is largely unexplored, possibly influenced by the pigs’ gut microbiome. This study examined the effects of N/P restriction on performance and N/P-related traits in growing-finishing pigs, while investigating heritability (h²), G×D, and the microbiome’s influence characterized by the microbiability (m²) on these traits. <br /> To achieve this, a 3-phase fattening trial was conducted under farm conditions, including 103 Piétrain×German Landrace pigs, originating from 20 artificial insemination boars (AI-boars). Half of the pigs were fed extremely N/P-reduced diets according to the German Agricultural Society (DLG), while the other half were fed strongly N/P-reduced diets. The animals did not show any impairments in performance under the extreme N/P restriction. Only under an N/P restriction stronger than originally intended a reduction in N/P intake and excretion was observed. Estimated h² varied depending on the trait and fattening period (h²: 0.00-0.77). The values of the AI-boar×feeding group interaction and the correlation coefficients between the AI-boars and feeding groups indicate a potential G×D for N/P intake and faecal N/P excretion. <br /> The gut microbiome was examined in 52 of the 103 pigs across four different gut sections (Jejunum, Ileum, Caecum, Colon). The N/P restriction showed only a limited effect on the microbiome composition. A clear distinction in gut microbiome composition was observed between the small (jejunum, ileum) and large intestine (caecum, colon). This difference in gut section microbiomes was also reflected by marked m² estimates for relevant traits. Specifically, the microbiome of the large intestine affected feed efficiency traits (m²: 0.26-0.61), whereas the microbiome of the small intestine influenced N/P digestibility (m²: 0.22-0.27). <br /> The estimated h² indicate a genetic foundation for most N/P-related traits, showing potential for genetic progress. Genotypes react differently to feed types, and the existence of G×D allows for selecting animals that maintain performance under strong dietary N/P restriction, enhancing robustness. The m² estimates show a clear influence of the gut microbiome on target traits, suggesting microbial information can help elucidate inter-animal variability and help in ranking breeding animals. Study results induce further interdisciplinary research in animal nutrition, breeding, and microbiology to enhance the efficiency of growing-finishing pigs.