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Optimizing protein sources in reduced-protein diets to improve the immune responses during coccidiosis in broiler chickens

Shanmugasundaram, R., A. Ajao, S. Fathima, A. Oladeinde, R. Selvaraj, T. Applegate and O. Olukosi

High dietary crude protein concentrations increase coccidiosis severity, and reduced-crude protein (RP) diets, supplemented with essential (EAA) and nonessential amino acids (NEAA), can improve the broiler’s immune response, which may depend on the plant protein source. The objective of this study was to compare the effects of soybean meal (SBM), canola meal (CM), or corn-DDGS (cDDGS) inclusion in RP diets for broiler chickens during an Eimeria challenge. A total of 1120 broiler chicks were distributed in a 4 × 2 (four diets × with or without challenge) factorial arrangement until d28 in seven replications. The four dietary treatments, fed between 7 and 28d, were (i) a standard diet with 20% crude protein (SP); (ii) RP (16%) corn-SBM (RP-SBM); (iii) a RP diet in which 8% CM replaced 6% SBM (RP-CM); and (iv) a RP diet in which 10% cDDGS replaced 5% SBM (RP-cDDGS). On d15, birds were challenged with 12,500 oo- cysts of E. maxima, 12,500 oocysts of E. tenella, and 62,500 oocysts of E. acervulina Eimeria (+E) oocysts. Samples were collected on d21, and the data were analyzed by a two-way ANOVA. There was a significant diet × Eimeria challenge interaction (P < 0.05) on bile anti-Eimeria IgG concentrations, splenocyte proliferation, macrophage nitric oxide (NO) production, and cecal tonsil IL-17 mRNA amounts. Birds in the RP-SBM +E group had higher (P < 0.05) bile anti-Eimeria IgG concentrations compared to the SP +E group. Though birds in the SP group had higher (P < 0.05) splenocyte proliferation than all other treatment groups, birds in the RP-SBM +E group had comparable splenocyte proliferation to the SP +E group. Within the E+ group, birds in the RP-SBM +E group had higher (P < 0.05) macrophage NO than the other groups. Birds in the RP-SBM +E group had higher (P < 0.05) IL-17 mRNA amounts in the spleen and cecal tonsils compared to the other treatment groups. Birds in the RP-cDDGS +E group had a lower (P < 0.05) CD8+:CD4+ ratio compared to the RP- SBM+E group.

It can be concluded that reducing the crude protein content of the grower diet by 4% (from 20% to 16%), achieved by reducing the SBM content of the diet, did not impair the host immune response to the Eimeria challenge. However, partial replacement of SBM with CM and cDDGS impaired the host immune response.