84 Relationships between feed protein fractions and the hindgut microbiome in the exercising horse

Abstract

The effect of dietary protein on the microbiome in the horse has limited data. In this study, 16 horses (averaging 606 kg BW) were used to evaluate the effect of protein source (forage, F, or forage and concentrate, FC) on hindgut microbiome. Horses were fed grass hay (timothy/orchardgrass). Those in the FC groups were also fed concentrate (Legends Growth, Southern States) at a ratio of 30:70 concentrate to forage. Horses consumed 2.44, 2.26 and 3.19 g CP/kg BW/d respectively for the F, FC(low and high CP) groups. Diets were fed for 14 wk. Horses participated in light exercise (1–2 h/d, 5 d/wk). Forage, concentrate and fecal samples were collected every 2 wk. Forage and concentrate samples were analyzed for CP, ADICP (acid detergent insoluble protein) and NDICP (neutral detergent insoluble protein). Fecal samples were analyzed for bacterial community abundance (PCR and sequencing). Statistical analysis of fecal communities was done using the Krustal-Wallis analysis and correlations determined using Slidewrite Plus. At the phylum level, there were positive linear correlations between the amount of daily CP from forage (g/kg BW/d) for both the F and FC groups for Proteobacteria (r = 0.54, P < 0.05), and Firmicutes (r = 0.55 and 0.7 respectively, P < 0.05). There was a positive linear correlation between ADICP and Proteobacteria for the FC groups (r = 0.8, P < 0.05). There was a linear correlation with Firmicutes (r = 0.59 and 0.82 respectively, P < 0.05), and quadratic correlations withBacteroidetes (r = 0.58 and 0.8 respectively, P < 0.05) and Tenericutes (r = 0.59 and 0.92 respectively, P < 0.05) for the FC and F groups with abundances increasing then decreasing for Bacteroides and vice versa for Tenericutes. For NDICP, there was a positive linear correlation with Firmicutes (r = 0.62, P < 0.05) and Proteobacteria (r = 0.52, P < 0.05) for the FC groups and for Fibrobacteres (r = 0.95 and 0.89 respectively, P < 0.05), while Bacteroides (r = 0.57 and 0.8 respectively, P < 0.05) as well as Tenericutes (r = 0.62 and 0.94 respectively, P < 0.05) had quadratic correlations with abundances decreasing then increasing for Bacteroides and vice versa for Tenericutes for FC and F groups. Nitrogen is needed in the hindgut for the microbiome and the changes observed in the Firmicutes and Fibrobacteres support this. In swine, excess dietary CP changed the microbiome that negatively affect gut health. This study suggests N has importance to the hindgut microbiome but also that excessive protein may impact the microbiome as well. Changes in the microbiome in horses due to diet which may affect fiber digestibility, gut and host health warrant further investigation in the horse.