Abstract
The aim of the present study was to compare intramuscular injection with a needle and intradermic needle-free vaccinations against porcine reproductive and respiratory syndrome (PRRS) in piglets at 28 days old by studying behavioral and physiological reactions. A total of 72 piglets divided into 2 sex-balanced batches were assessed. Within each batch, the piglets were divided into three treatments, which were Hipradermic (0.2 ml of UNISTRAIN® PRRS vaccine administered with an intradermic needle-free device), Intramuscular (IM, 2.0 ml of vaccine), and Control (not vaccinated). Before the vaccination, the piglets were trained to cross a 4-m-long raceway to perform an aversion learning test. The day of vaccination, the time taken to cross the raceway was registered for each piglet at different times: prior to the vaccination and 10 min, 2, 24, 48, and 72 h after the vaccination, to measure variations in these times as signs of aversion to the vaccination process. Vocalizations, as potential signs of pain, were recorded as well at the end of this raceway to analyze their frequency (Hz), duration, and level of pressure (dB) at the moment of vaccination. Salivary cortisol, as a sign of the HPA-axis activity, was assessed 10 min after the vaccination. In addition, activity budgets, local reaction to the vaccine, and serological titer were also considered in the study. Ten minutes after the vaccination, the IM piglets took longer (p < 0.001) to cross the raceway than did the Hipradermic and Control piglets. Vocalizations were significantly different between the three treatments: the Control piglets produced vocalizations with the lowest frequency (p < 0.001) and level of pressure (p < 0.001), and IM with the highest, with Hipradermic in a significant intermediate position (p < 0.001). Accordingly, the day of the vaccination, IM and Hipradermic animals were lying on the side of the vaccine administration a greater proportion of time than were the Control piglets (10, 11, and 6%, respectively; p = 0.027). Salivary cortisol was not significantly different between treatments. The serum titer of antibodies against the PRRS was higher (p < 0.001) in both vaccinated treatments in comparison to the Control piglets. It is concluded that the Hipradermic needle-free vaccination may result in a less aversive experience in piglets than did intramuscular vaccination.
Highlights
Pigs might be vaccinated by several routes, for instance, orally, intranasally, intravenously, or delivered onto, into, under, or across the skin or into a muscle
The piglets were distributed into three groups according to the vaccination treatment: [1] Intramuscular vaccination (IM) by means of a single intramuscular injection in the neck region with 2.0 ml of UNISTRAIN R using an individual, stainlesssteel needle of 21 G x 16 mm; [2] Hipradermic vaccination by means of a single needle-free intradermal application with 0.2 ml of UNISTRAIN R in the neck region using the Hipradermic R device, which is a battery-powered injector; and [3] Control treatment without vaccination and where the piglets were just touched in the neck region following the same handling procedure as the pigs in the previous groups
A total of 93 vocalizations were registered during the vaccination corresponding to 5 in Control, 31 in Hipradermic, and 57 in IM treatment, as the same animal could have more than one vocalization during the vaccination
Summary
Pigs might be vaccinated by several routes, for instance, orally, intranasally, intravenously, or delivered onto, into, under, or across the skin or into a muscle (epicutaneous, intradermal, subcutaneous, transdermal, and intramuscular, respectively). Needle-syringe devices have been the predominant method for vaccine and drug delivery for pigs, usually by means of intramuscular administration. This procedure has been considered as potentially painful [1], resulting in acute and long-term fear [2]. Using mechanical compression to force fluid through a small orifice, these devices produce a high-pressure stream 76–360 μm in diameter (compared to 810 μm for a 21-gauge needle) that penetrate skin and subcutaneous tissue ensuring a homogenous process where each animal is vaccinated at the selected tissue depth [11]. In the case of the intradermal application of vaccines, it is important to adequately adjust the pressure and force of the needle-free device to ensure a deposit of the vaccine at the dermis layer
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