| In recent years, heat stress has caused enormous economic losses in the global animal industry. To alleviate the effect of animal heat stress on laying hens, we investigated the feasibility and mechanism about probiotic mixture of Enterococcus faecium HDRs Ef1 and Bacillus subtilis HDRa BS1, which would lay the theoretical foundation and practice basis for the development of new anti-stress biological agents.A total number of 856 Hy-Line Brown commercial laying hens, with the 280 days of age and similar egg production rate, were selected in the experiment. The layers were then randomly divided into three groups: the control of high temperature group(33℃), the probiotic mixture group [100 g/t Enterococcus faecium(5 billion CFU/g) + 400 g/t Bacillus subtilis(10 billion CFU/g) + 33℃) and the control of room temperature group(26℃), each group consisted of three repeates. all laying hens were fed with corn-soybean based diet. The experiment period was 20 days. Experimental results and conclusions are as following:Production performance and egg quality: during the whole period, the egg production rate, average daily feed intake, average egg weight of the probiotic mixture group had increased by 3.99%(P < 0.01), 6.29%(P < 0.05) and 3.29%(P < 0.05), compared with the high temperature group. But less than the level of room temperature group. In addition, the FCR, diarrhea rate, broken egg ratio and mortality of chickens had reduced. Howerer, aspects of shell thickness, strength, albumen height, egg yolk color and haugh unit had increased by 4.35%(P < 0.05), 16.72%(P < 0.05), 15.19%(P < 0.05), 5.66%(P > 0.05) and 6.56%(P > 0.05), respectively.Blood indicators: compared with the high temperature group, the probiotic mixture group was reduced by 28.38%(P < 0.05), 46.07%(P < 0.05) and 31.68%(P < 0.05) in terms of serum IL-1, endotoxin and epinephrine, respectively. Meanwhile, IL-10 and progesterone had increased by 137.34%(P < 0.05) and 83.52%(P < 0.05), respectively. However, no significant difference(P > 0.05) in terms of TNF-α and ND-Ig G.Intestinal barrier function: analyzed the specific number of bacteria in ileum and cecum with Real-time PCR technology, we found that probiotic mixture had significantly reduced the number of E.coli in the cecum(P < 0.05) and increased the number of lactobacilli in the ileum(P < 0.05) to improve the imbalance of intestinal flora. Meanwhile, it demonstrated the probiotic mixture could significantly up-regulated the m RNA expression of many genes, including the tight junction protein occludin, ZO-1(ileum, cecum) and JAM-A(cecum)(P < 0.01), the ileal and cecal mucosa repair gene of EGF(P < 0.01), the ileal and cecal mucous protein MUC-2 gene(P < 0.01; 10 d) through the Real-time PCR technology analysis. Next, histological section results indicated that the probiotic mixture could observably improve intestinal villus height(P < 0.01), while no pronounced variation of the crypt depth was observed(P > 0.05). Moreover, we further examined that the probiotic mixture had up-regulated the protein expression and secretion of Immunoglobin A(Ig A) through Western-blot analysis.In a word, adding the probiotic mixture could improve the balance of intestinal flora, repair the intestinal mucosa, up-regulate the expression of the tight junction protein, multi-level enhance the intestinal barrier function. And that could significantly reduce the content of core factors in the serum, such as endotoxin and IL-1, effectively alleviate the symptoms of heat stress of laying hens and improve the growth performance and egg quality. |
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