The huge consumption of antibiotics by human and animal industry in the world has resulted in severe problems of bacterial resistance and drug residue，the rate and probability of the occurrence of“superbacteria” increased significantly，presenting threat to human and animal health. Although developed countries such as the Europe union and the United States of American，and our country，have successively issued a series of policies to decrease the consumption of antibiotics，its use in some developing countries such as Africa and Southeast Asia，still is insufficiently supervised and excessive used，and the long?term threat of bacterial resistance still exists. Therefore， the search of effective natural products to reduce the use of antibiotics is vital. Now，Chinese herbal medicine， probiotics，antimicrobial peptides，acidifiers，enzyme，and animal used marine drugs，all showed excellent antibacterial，anti?inflammatory，immunity enhancement，and growth?promoting functions. A green，antibiotics?free breeding technology in animal industry is of tendency in future. This paper reviewed the current situation of antibiotics used in China，as well as the antibiotics replacement products，focused on their function and acting mechanism， problems occurred in usage，and possible solutions for dealing with these problems.

To observe the protective effect of Chitosan ? Gentamicin conjugate（CS ? GT）on Dextran Sulfate Sodium（DSS）? induced colitis in mice. Thirty healthy SPF male C57BL / 6J mice were randomly divided into 5 groups：Control group，DSS group and low，medium and high dose CS?GT group. Taking daily clinical observation and recording of mice activity，diet，body weight and fecal occult blood. All animal were euthanized and blood，colon tissues were collected on the 14th day. The changes of intestinal mucosal，the concentration of serum biochemical indexes and inflammatory factors were determined by optical microscope，biochemical analyzer，and ELISA，respectively. The results showed that compared to the control group，the body weight，and colon length were decreased in DSS?treated mice（P<0.01）. Meanwhile，we observed serious bloody stool and intestinal villus dropped in this animal. The concentration of serum ALB and TP significantly decreased（P<0.01），as well as the decrease of anti? inflammatory factors IL?4 and IL?13. But the concentration of pro?inflammatory factor IL?6 was significantly increased （P<0.01）. Compared with DSS group，the body weight and colon length of mice in medium and high dose CS?GT groups were significantly increased（P<0.05），the bleeding was improved，and the level of serum ALB and TP increased significantly（P<0.05）. The expression level of pro?inflammatory factor IL?6 decreased significantly（P< 0.05），and the anti?inflammatory factors IL?4 and IL?13 trend to increase trendy. Our results suggested that CS?GT has a significant protective effect on DSS?induced colitis in mice and is valuable to development as a functional feed additive for animal intestinal protection.

With the increasing of pig industry scale in China，the risk of various stress pathogenic factors is serious to host health. Stress not only leads to the decline of production performance，such as feed intake，daily weight gain，meat quality，and reproduction rate of pigs，but also causes the damage of intestinal mucosal barrier， inflammatory response，and immunosuppression of the host. Consequently，the risk of outbreak of infectious diseases is increased that seriously affects the breeding efficiency and epidemic prevention effect. This paper reviewed the common risk factors in scale pig farm，such as weaning stress，heat stress，immune stress，transportation stress，and pre ? slaughter stress. We focused on the causes，hazards，pathogenesis and prevention and control techniques of various stress，so as to provide basis for the control of stress?induced disease.