Milk Kefir as a Natural Probiotic, Individually or in Combination with Organic Acids in Broiler Chickens: Influence on the Immune-Related Gene Expression, Intestinal Morphology, Microbiota Activity, and Serum Biochemistry

The objective of this study was to examine the influence of the addition of milk kefir (MK), as a natural probiotic to drinking water, individually or in combination with organic acids (OA), on the growth performance, intestinal microbial counts and morphology, serum metabolites and immune status in broiler chickens. Two hundred and fifty one-day-old broiler chicks (Ross 308) were randomly distributed into 4 treatment groups including a control group, and the control group with MK (2% of drinking water), OA (350 mL/1000 L of water), or MK+OA. At d 35, Body weight gain, feed intake, and feed conversion ratio were recorded. At the end of the experiment (d 35), five birds per treatment were selected to determine the bacterial population, serum biochemical metabolites, and intestinal morphology. According to the results, water supplemented with MK increased the mRNA levels of IFN-γ and IFN-β at 35 d in the jejunum (P < 0.05). OA supplementation significantly increased the gene expression of IL-6 (P < 0.05). On the other hand, the gene expression of IL-12 increased in broilers fed the control diet (P < 0.05). The broiler chickens that received MK+OA showed an improvement in feed conversion ratio (P < 0.05) compared with OA and control groups. The addition of MK+OA resulted in a higher relative weight of thigh in broiler chickens compared with the MK group (P < 0.05), while the relative weight of spleen was lower in OA and MK treatments compared with the MK+OA group (P < 0.05). The results also indicated that the addition of MK+OA decreased the ileocaecal E. coli population compared to other treatments (P < 0.05). Conversely, the birds that received MK+OA had a higher viable count of ileocaecal lactobacilli (P < 0.05) compared with the OA group. In conclusion, the combination of OA with MK had beneficial effects on the performance, intestinal immune-related genes, and gut microbiota activity of broiler chickens.