The pork industry loses a substantial amount of money each year due to the trimming of pork carcasses in processing plants. A large portion of carcass trimming is due to the presence of abscesses on pork carcasses. These abscesses form in many locations, however abscesses are frequently seen at sites where injections of vaccines and antibiotics are commonly given. The most common form of administering injection is by the use of a needle-and-syringe system. An emerging technology available to swine producers that can be used to replace these needle-and-syringe systems is needle-free jet injection. Needle-free jet injection delivers vaccines by using a pressurized gas to force the vaccine through the skin of the animal rather than a traditional hypodermic needle. Therefore, the purpose of this experiment was to determine if there was a difference in the rate of abscess formation when comparing needle-free injection and conventional needle-and-syringe injection methods.
We utilized 198 nursery age pigs for this trial. The trial began after the pigs were allowed to adjust to the environment of the Kansas State University Segregated Early Weaning (SEW) unit for 21 days. On the first day of the trial each pig received 4 injections of aluminum hydroxide adjuvant. On one side of the pig, injections were given in the neck and ham using a needle-and-syringe system. On the opposite side, a needle-free jet injection system was used to administer one injection in the neck and another in the ham. Immediately prior to injection, the surface of the skin where the injections were given was contaminated with an inoculum of Arcanobacterium pyogenes, a bacterium that is commonly associated with abscesses found in livestock carcasses. Pigs were then fed for 27 and 28 days. On days 27 and 28, the pigs were humanely euthanized and then sent to the Kansas State Veterinary Diagnostics Laboratory where necropsies were performed on each animal and each injection site underwent histopathological evaluation to determine where abscesses had formed.
In this project there were a total of 792 injections given. Of the 792 injection sites that were evaluated, histological evaluation uncovered only 13 abscesses at those locations. Of the 13 abscesses found, 12 were found at injections sites that utilized the needle-free jet injection system and 1 was found for the needle-and-syringe injection system. When comparing neck and ham injection sites, 5 abscesses were found at neck injection sites and 8 were found at ham injection sites. 10 of the abscesses observed were on the left side of the animal while 3 were found on the right side. Additionally, granulations formed as a result of immune reaction to the adjuvant were not different between the two injection methods.
The results of this study indicate that abscess formation due to injections is very hard to reproduce in a controlled experiment. Additionally, there does not seem to be a difference between the rates of abscess formation between the neck and ham regions. However, this experiment suggests that the utilization of these needle-free systems has the potential to increase the occurrence of abscesses when A. pyogenes is present.
