Antibiotics are essential for disease prevention and treatment in pig farms. Good use of antibiotics can prevent and treat diseases. Poor use of antibiotics can cause waste, poisoning and even death.
Because of the uneven quality of piggery practitioners, little knowledge of diseases and veterinary antibiotics, there are inevitably mistakes in practice. If antibiotics are not selected properly, sometimes the dosage is too large, sometimes the dosage is too small; or unfamiliar with the characteristics of drugs, random compatibility, not only affect the efficacy of drugs, but also cause significant losses.
1. Interaction of antibiotics, bacteria and organism
1.1 Antibiotics and Bacteria
1.1.1 Antibiotics have broad spectrum (e.g. tetracyclines) and narrow spectrum (e.g. penicillin) for bacterial antibiotics. They can either kill bacteria (e.g. penicillin) or inhibit bacteria (e.g. tetracyclines). The bactericidal or bacteriostatic effects depend on dose-effect relationship and time-effect relationship. The so-called dose-effect relationship means that within a certain dose range, the effect of drugs increases with the increase of dose. The so-called time-effect relationship means that the effect of drugs changes with time. Different antibiotics have different antimicrobial spectrum and activity.
1.1.2 Bacteria are naturally resistant to antibiotics. For example, most Gram-negative bacteria are naturally insensitive to penicillin, while others are acquired. If bacteria are exposed to low doses of antibiotics for a long time, they will gradually develop resistance to antibiotics, and They are resistant to the same antibiotics. If a bacterium is resistant to aureomycin, it is resistant to oxytetracycline and doxycycline. Drug resistance can also be inherited, that is, the first generation of drug-resistant bacteria can pass resistance to the next generation or generations. After a period of antibiotic withdrawal, the bacteria may gradually recover their susceptibility to antibiotics.
1.1.3 Drug susceptibility test is carried out in vitro. Because different drugs have different pharmacokinetics, they are not sensitive to drugs in vitro and in vivo, but sensitive drugs in vitro are not necessarily effective in vivo because of different absorption and distribution. Therefore, antibiotics can not be selected according to the results of in vitro susceptibility test.
1.2 Antibiotics and the Body
1.2.1 Antibiotics can have side effects on the body, such as allergy, poisoning and so on. There is no clear distinction between drugs and poisons. Drugs can become poisons when they are used in excess or in incorrect ways. Sometimes long-term use of antibiotics may result in imbalance of bacterial flora in the body, or the lack of vitamins produced by the metabolism of some beneficial bacteria. The properties of drugs such as water solubility, liposolubility, molecular weight and polarity can affect the absorption and distribution of drugs in vivo.
1.2.2 The body can participate in the absorption, distribution, biotransformation and excretion of antibiotics. Some metabolized products still have antimicrobial activity, while others lose their antimicrobial activity. Some drugs, such as telmicocin and doxycycline, have higher concentrations in lung tissues than in plasma, so they are more effective for respiratory diseases. Most drugs can not penetrate barrier structure, such as blood-brain barrier. In the case of encephalitis, the ability of some drugs to penetrate the blood-brain barrier is significantly improved due to changes in permeability.
1.2.3 The nature and functional state of antibiotics affect the pharmacokinetics of antibiotics. It is difficult to remove bacteria in vivo, whether it is bactericidal antibiotics or bacteriostatic antibiotics. Therefore, the role of antibiotics is mainly to control the number of bacteria in the body, while the elimination of bacteria depends on the body's immunity and phagocytosis ability.
1.3 Bacteria and organism
1.3.1 Bacteria can infect organisms through different portals, multiply in vivo and distribute to specific target organs or tissues, causing specific pathological changes and clinical symptoms. Some bacteria are pathogenic by toxins, others depend on their own pathogenicity.
1.3.2 The immunity of organism can produce immunity to bacteria, and resist bacterial infection through non-specific and specific immunity. A specific bacterium can cause a pig disease at a certain stage, mainly because the immunity of this group is insufficient, E. coli mainly causes the incidence of suckling piglets and weaned piglets.
1.3.3 The use of antibiotics can reduce the number or density of pathogenic bacteria in vivo, and improve the resistance of animal organisms to pathogenic bacteria through immunization or adaptation process. If the reserve sows are exposed to E. coli in pig farms during adaptation, they will slowly produce immunity against E. coli, which can provide higher levels of antibodies after delivery.
2. Pay attention to the route of administration
The routes of administration include injection, oral administration, aerosol, skin and topical administration, while the common routes of administration in pig farms are intramuscular/intravenous injection and oral administration. These two approaches have their own advantages and disadvantages, and can not be completely replaced. Different routes of administration can directly affect the absorption rate and concentration of drugs, thus determining the speed of drug action, the duration of maintaining drug efficacy and the strength of drug efficacy.
2.1 Injection can be divided into intramuscular injection, subcutaneous injection, intradermal injection and intravenous injection. The advantages of injection are fast absorption, high bioavailability, not affected by intake and drinking water, and accurate individual dosage. The drawback is that the amount of labour is heavy and the stress on pigs is strong. Subcutaneous and intradermal injection is difficult to operate and less used.
2.2 Oral administration can be divided into oral administration, mixed drinking and mixed feeding. Among them, the dosage is accurate, but it needs individual operation. It is mainly used for piglets. The advantages of mixed drinking and feeding are convenient, convenient for group medication and labor saving. The disadvantage is the inaccuracy of quantification.