This figure shows the number of pseudorabies virus- (Aujeszky's disease-) positive animals in a herd by parity distribution. This 1600-sow herd had been purchasing PRV-negative gilts for 1 year, and double vaccinating them in an offsite isolation unit prior to introducing them into the herd. Gilts are blood tested before leaving isolation to be sure they are PRV negative. Currently the entire sow herd is being vaccinated on a quarterly basis.
What can you tell from this figure about the effectiveness
of the vaccination/eradication program?
For the 5 months prior to generating the report that resulted in Figure 1 (front cover, and repeated here), all sows in the farrowing house had been blood tested for PRV with the intention of culling all positive sows at weaning. Unfortunately, there were several weeks in a row when > 75% of the sows in any given week came back PRV-positive. To meet breeding targets, some positive sows had to be rebred.
Using a herd records database such as PigCHAMP(R), it is possible to effectively track PRV-positive animals in a herd. As you can see from Figure 1, this herd has a number of animals that are PRV-positive in parities >= 5. It also appears that there are some PRV-positive animals in parities one and two. From Figure 2, you can see the overall parity distribution of the herd compared to the PRV-positive distribution.
Our clinic uses the PigCHAMP(R) "USER1" location under sow records Æ record details to code in positive or negative PRV test results on the individual animals when the results come back from the lab. We have found this especially beneficial during the eradication process to follow sows that were tested during gestation and were suppose to be removed postweaning.
This "USER1" ID is an excellent way to keep track of positive animals throughout subsequent gestations and farrowings to make sure that they eventually get removed. It can also be used to track seroconversion rates of animals that go from negative to positive and to make sure that incoming gilts were staying negative. For example, as Figure 1 shows, midway through the eradication process in this example herd, a majority of younger animals were remaining seronegative while there were still seropositive animals in the older parities. Eventually we were able to remove these positive animals and eradicate PRV from this herd. The sows' parity, location, and removal information was already being tracked through the PigCHAMP(R) system. We were also able to generate lists of positive animals by using the List Data function under Database Applications using USER1= "Positive" as the filter. We were also able to get the entire herd picture by using the Report Type.....Break Down with the Row Cross tabulation variable as parity and the column cross tabulation variable as User1 (Table 1). This system could also be beneficial for monitoring the eradication of other diseases, such as porcine reproductive and respiratory syndrome virus (PRRSV).
The weakness of the system is that on occasion animals with lost tags get coded back in as "Parity 1" animals when they are retagged in the farrowing house. This makes it appear that you have seroconversion occurring in younger animals when in reality it is just older animals that are seropositive. This was the case in the above example: the parity-one and parity-two positive females were misidentified by parity.