Eliminating porcine reproductive and respiratory syndrome(PRRS)virus from a breeding herd is not a simple task,and no herd acts exactly like the next,according to Brad Leuwerke,DVM,with Swine Vet Center,St.Peter,Minnesota.
Looking back at years of PRRS elimination efforts,Leuwerke led a retrospective analysis of several breeding herds to determine why some were able to stay on course and achieve success while others were unsuccessful.
“We assessed several factors thought to influence a return to PRRS stability,”he said.“We found the season when the outbreak occurred,the virus strain causing the outbreak and the herd’s previous PRRS status all substantially affected the time necessary to eliminate the virus from the breeding herd.
“不过，在很大程度上这些因素往往不在我们的掌控内。”
“Largely,though,it feels like these factors are often out of our control.”
The review did highlight four factors producers can control that help drive successful virus elimination.“Failure to account for these aspects will extend the time necessary to achieve negative status,”Leuwerke said.
Producers must resist the urge to bring in extra replacement animals as a herd closure progresses.If replacements are brought in before the virus is eliminated,these animals will become infected and the closure time is drawn out.
“Instead,herds should‘load up’with replacements at the beginning of the closure to withstand the temptation to open up before the virus is eliminated,”Leuwerke said.“In addition,a reduction of culling,starting early in the closure,will also help in maintaining production goals without needing to open the herd.”
2）将全群暴露日设为“第零天”
2)Set‘day zero’with an entire herd exposure
将整群直接暴露于病毒的那一天指定为PRRS净化的“第零天”。
Start the PRRS elimination on a specified“day zero”using direct virus exposure of the entire herd.
Leuwerke说：“同时感染整群可使封群时间达到最短，优于让病毒在猪群中自然传播。”
“Infecting the entire population at one time allows for the shortest closure possible and is preferred over allowing the virus to naturally move through the population,”Leuwerke said.
这对于较新的、毒力更强的PRRS株尤其重要，因为这些毒株感染的动物排毒时间更长。
This is especially important with newer,more virulent PRRS strains that look to have longer periods that animals shed virus.
3）掌控分娩舍生物安全
3)Manage farrowing biosecurity
繁殖群封群末期，分娩舍是最后一个病毒出没的地方。
As a breeding herd nears the end of the closure,farrowing is the last place the virus can be found.
“The last animals to harbor and shed virus will do this through piglets,either born virus-positive or infected following birth,”Leuwerke explained.“Our biosecurity practices late in a closure influence the length of closure and,ultimately,if elimination is successful.”
At this stage,pigs should not be held back at weaning for more growth.“This is one of the worst things we can do in a sow herd working towards PRRS-negative status,”he said.It will extend the time of elimination.
Farrowing sanitation is very important,and poor practices can cause the elimination to fail.Leuwerke recommends all-out farrowing rooms at weaning so the rooms can be thoroughly washed,disinfected and dried.Common hallways also must be washed after all pig movements.
仔猪处理的工具也必须保持良好的卫生，以防止病毒在窝间传播。
Good hygiene with processing tools must be practiced,too,to prevent the virus from spreading between litters.
“Newer monitoring strategies that allow us to test more animals have given us more confidence that a herd is truly negative before reopening to replacement animals,”Leuwerke said.
这些最新的策略包括使用猪群中许多动物的处理液。
These new strategies include the use of processing fluids from many animals in the population.
“Before the use of processing fluids,we often would blood test 30 piglets each month,”he explained.“If we had 3 consecutive months negative,we called the herd negative.We likely missed virus using these testing procedures.”
Leuwerke承认消除PRRS是困难的。但在猪群封群前做好规划将有助于规避净化失败的常见错误。
Leuwerke admits PRRS eliminations are difficult.But good planning before a herd closure starts will help avoid common mistakes that lead to elimination failures.
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