Decay Patterns of Maternal Antibodies in Piglets and Reference Immunization Ages
Decay Patterns of Maternal Antibodies in Piglets and Reference Immunization Ages
I. Rise and fall patterns of maternal antibodies for classical swine fever
Classical swine fever is an acute, febrile and highly contagious infectious disease caused by classical swine fever virus. Research data show that 0-day-old piglets that have maintained colostrum intake have no classical swine fever maternal antibodies; maternal antibodies against classical swine fever reach a peak at 1 day of age and then gradually decline. Classical swine fever maternal antibodies provide protection for piglets from 1 to 28 days of age, and a small number of pigs are still protected at 35 days of age. However, the presence of maternal antibodies is also an important factor leading to poor immune efficacy of classical swine fever vaccines in piglets, so determining the correct age for the first immunization is very important. Through experiments, the first immunization of piglets should be carried out at 28 to 35 days of age, which can achieve a relatively qualified immune protection rate and is an important guarantee for avoiding classical swine fever during the nursery stage. At the same time, monitoring of classical swine fever antibodies in the herd should be done well.
II. Rise and fall patterns of maternal antibodies for circovirus
Research data from Zhang Yi et al. (2012) show that when test sows were immunized with circovirus vaccine before farrowing and the maternal antibodies of newborn piglets were tested, PCV2 maternal antibodies were almost undetectable in newborn piglets before suckling; after suckling colostrum they gradually rose, and maternal antibody levels were highest at 10 to 20 days of age and reached a peak at around 20 days of age; after 30 days of age they declined rapidly, and at around 40 days of age they fell to the critical value. Therefore, immunization with circovirus vaccine at 14 to 20 days of age is optimal. The relatively high maternal antibody levels in suckling piglets can reduce the occurrence of PCV2 viremia in serum, thereby inhibiting PCV2 replication in the body, protecting piglets from PCV2 infection in the early stage, and reducing the amount of virus in piglet feces, serum and immune organs. After sows are vaccinated with PCV2 vaccine, infection of piglets by this virus declines, but this does not mean that the entire piglet herd on the farm has received complete protection. For piglets to be completely protected, the piglets themselves must be immunized with circovirus vaccine. Foreign research has confirmed that low early colostrum intake by piglets is a major factor causing post-weaning multisystemic wasting syndrome. Therefore, in production practice, scientifically carrying out circovirus vaccine immunization of sows and piglets and ensuring that newborn piglets receive sufficient colostrum in a timely manner are the keys to ensuring that the piglet herd has good immunity.
III. Rise and fall patterns of maternal antibodies for porcine reproductive and respiratory syndrome
Porcine reproductive and respiratory syndrome is a disease that is commonly infected in pig farms and causes sustained losses, and the immunization program is very important. Research by Du Xizhong et al. (2012) shows that maternal antibodies for porcine reproductive and respiratory syndrome begin to decline sharply at 21 days of age, with a half-life of about 9 days, and around weaning the maternal antibodies basically decline to the critical value. Research results by Han Xiangui (2011) show that, based on test results of immunization with live porcine reproductive and respiratory syndrome vaccine at 14, 21 and 28 days of age, immunization at 14 to 21 days of age has the best effect. According to the rise and fall patterns of maternal antibodies for porcine reproductive and respiratory syndrome, the antibody-dependent enhancement (ADE) unique to porcine reproductive and respiratory syndrome virus, and the characteristic that live porcine reproductive and respiratory syndrome vaccine produces neutralizing antibodies slowly, immunization with live porcine reproductive and respiratory syndrome vaccine should be earlier rather than later. Immunization at 14 to 21 days of age is recommended, and at the same time monitoring of porcine reproductive and respiratory syndrome virus antibodies in the sow herd and monitoring of porcine reproductive and respiratory syndrome stability in commercial pig herds should be done well.
IV. Rise and fall patterns of maternal antibodies for pseudorabies
Pseudorabies is a disease that can seriously affect the economic benefits of commercial pigs on pig farms, so prevention and control of pseudorabies must be strengthened. First, the changes in pseudorabies maternal antibodies must be understood. According to research by Du Xizhong et al. (2012), immunizing sows 30 days before farrowing can enable piglets to obtain relatively high maternal antibodies, but the protection period of currently available pseudorabies vaccines on the market is 4 to 5 months, so it is recommended that sow immunization adopt a mass immunization method of 3 to 4 times per year. As piglets grow older, maternal antibodies begin to decline, and the antibody positive rate drops from 100% at 4 weeks to 54.55% at 10 weeks of age, with the fastest decline at 6 to 8 weeks of age. Research by Du Xizhong et al. (2012) also shows that when piglets are immunized before 5 weeks of age, both the pseudorabies virus gB antibody positive rate and the S/N value conversion value decline, indicating that maternal antibodies may inhibit the establishment of active immunity in piglets. After vaccine antigen neutralizes maternal antibodies, the antibody level after immunization is lower than the maternal antibody level during the same period. Therefore, in designing the pseudorabies vaccine immunization program, overcoming the inhibition of active immunity in piglets by maternal antibodies obtained through passive immunity is key. It is recommended that the age for first immunization of piglets against pseudorabies be set at 6 to 8 weeks of age. According to testing findings on affected pig farms in 2012, the pseudorabies virus antibodies of finishing pigs at around 120 days of age are basically 0, so it is recommended to strengthen immunization with pseudorabies vaccine once at 10 to 12 weeks.
V. Rise and fall patterns of maternal antibodies for foot-and-mouth disease
Foot-and-mouth disease is a severe infectious disease characterized by vesicular lesions. Research results by Yu Qiong et al. (2012) show that 0-day-old piglets that have not consumed colostrum all have no maternal antibodies; maternal antibody titers in 1-day-old piglets reach a peak and then gradually decline. Foot-and-mouth disease maternal antibodies provide protection for piglets from 1 to 14 days of age, and some piglets are still protected at 21 days of age. At 21 days after the first immunization at 28 to 35 days of age, the qualified rate of immune antibodies is below 70%; after 28 days it reaches a peak of 86.7%; if immunized once more 1 month later, the effective immune antibody level can be maintained for a longer time and then gradually declines, and by 5 months later it can no longer provide protection. Research by Zeng Cunfang et al. (2010) recommends boosting foot-and-mouth disease immunization once in finishing pigs at around 120 days of age to ensure the immune effect against foot-and-mouth disease.