The impact of extruded soybean processing temperatures conditions on broiler’s ileal and cecal microbiota composition and function

Optimal soybean (SB) processing conditions is essential to ensure that antinutritional factors as trypsin inhibitors are deactivated while maintaining protein solubility and dispersibility. Heat processing is critical for improving amino acid digestibility of extruded SB for broilers. Excessive heat treatment can lead to denaturation of proteins, resulting in a negative impact on animal performance and microbiota composition.

In this study, we investigated the effect of three different processing temperatures (182,199, and 154°C) for normal-control (NC), overcooked (OC), and undercooked (UC) SB on microbiota composition and function in broilers. Male Cobb 500 broilers (1,860) were fed with 3 batches of expeller SB, randomly allocating them to the three treatments with 10 replicate floor pens/diet (62 birds/pen) from 0 to 35d of age. Ileal and cecal content were collected from one bird/pen at d 7, 14, and 28 for 16S sequencing.

Sequences were processed using DADA2, and diversity analysis was focused on the genus level. Alpha diversity, measured as Shannon index, significantly increased with time for both ileal and cecal samples, and PERMANOVA of Bray-Curtis distance showed that beta diversity also differed significantly between all-time points. Functional profiles were interpolated from 16S data using PICRUSt2, based on the MetaCyc database. In the ileal content samples, alpha diversity of NC samples was higher than OC or UC samples only at d28. Treatment affected ileal beta diversity at d14 and d28, with all treatments separated from each other.

We observed a cluster of OC samples separated from NC or UC samples in PCA. In the ileal contents, OC samples had a significantly higher abundance of two Lactobacillaceae genera. In the cecal contents alpha diversity measured with Shannon index was not affected by treatment. Treatment also affected cecal contents beta diversity at d14 and d28, with OC samples showing the most distinct differences.

At d14, OC samples had higher abundance of several Lactobacillaceae genera in the cecum. At d28, OC samples showed higher levels of Akkermansia, Lactobacillus, Bacteroides, Streptococcus, and Staphylococcus. On the functional level some pathways were mainly driven by age. Carbohydrate degradation-related pathways were reduced with age, while amino acid degradation pathways increased with age in both ileum and cecum.

At d28, OC and UC samples had reduced myo-inositol degradation pathway in the ileum, which is a strict anaerobic process. In conclusion, inappropriate SB processing temperatures can significantly impact the microbiota composition and function in the digesta within the ileum and cecum, especially in older broiler birds with a more pronounced effect observed with higher extruder temperature.

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