Background

Public concern regarding painful livestock procedures such as castration is increasing, report Drs Jennifer Brown, Joseph Stookey, Jane Alcorn, Yolande Sedon and Fiona Lang as well as Tracy Muller and Megan Bouvier. Piglet castration has been criticised, largely because pain medication is not commonly used. The cost and labour required to administer analgesics to individual piglets are the main deterrents to producers adopting this practice.

Having an affordable and practical method for delivering pain medication would likely increase the acceptance of this procedure and use of pain medication by producers.

Previous studies with cattle have shown that analgesics can be transferred through milk at lactation. However, there is a lack of research on swine and the degree of passive transfer of these drugs to offspring.

The objective of this study was to determine if the analgesic, Meloxicam®, can be delivered to the piglets via the sow. The study was conducted in three parts, with the first objective being to determine if a) pan medication can be passed via the milk and b) the drug concentration found in milk. The second objective was to determine the most effective time period that will provide the maximum transfer of drug to piglets, and the third objective was to determine whether this method is effective at reducing pain responses during or after castration.

Figure 1. Piglet chute used for behavioural observations after castration.
The behaviour of pigs in the chute and time taken to return to the sow will be used to measure pain relief.

Translactational Analgesia

The first experiment studied the transfer and excretion of analgesic in milk. Twelve sows were injected with Meloxicam at seven days post-farrowing, with each sow receiving one of three dosages. After the injection, multiple blood and milk samples were collected over a five-hour period.

The samples were, at the time of writing the article, being tested for drug concentration and will indicate the amount of drug transferred through milk and how drug levels change over time. Based on these results, the authors will determine an 'optimum' drug dosage and timing that may be effective at reducing pain at castration.

In the second experiment, the researchers will inject sows and collect blood samples from piglets to see if appropriate levels of analgesic are transferred to piglets.

A third and final experiment will involve 24 sows and 144 piglets and will assess whether translactational analgesia is effective at reducing pain. Some sows will receive the analgesic and some a saline injection as a 'control' treatment.

Piglets will be castrated one or two hours after sow injection, and using a variety of measures, piglet pain will be assessed at the time of castration and for up to 24 hours following castration.

Some piglets will not be castrated but will receive a sham treatment involving handling similar to that used for castration. This will help the authors to determine the difference between the actual pain of castration and the piglet's reaction to handling.

Measures used to evaluate pain relief will include piglet vocalisations at the time of castration and behaviour of a 24-hour period following castration - lying, standing, time spent suckling. Meloxicam is a non-steroidal anti-inflammatory (NSAID) drug, similar to aspirin, and is expected to reduce pain and inflammation following castration but is unlikely to have a noticeable effect on pain at the time of castration.

Previous studies have shown that there is little difference in the behaviour of castrated and non-castrated piglets within the farrowing crate; piglets generally continue to feed and rest with their littermates following the procedure with only minor changes in posture and movement.

Therefore, as a method to identify pain, piglets will be observed manoeuvring in a chute and hurdles (Figure 1) for indications of pain or discomfort approximately 20 minutes after castration. The piglet must raise its hind legs in order to cross the hurdle and therefore, it is expected there will be differences in the length of time it takes a piglet to manoeuvre along the chute and over the hurdles if experiencing discomfort from castration. The piglet is placed in the wooden chute at the back of the farrowing crate and must walk down the chute to return to the sow. To ensure that the piglets are familiar with the chute, they will be trained on the day before by placing them into the chute and letting them learn how the find the exit.

Bottom Line

With the growing awareness of animal welfare issues in the public, there is an increasing need for alternatives to painful procedures such as castration. Finding a practical and economic way of providing pain relief would enable producers to address this problem effectively, while also improving piglet welfare. Using translactational medication for pain relief would be much easier to implement than injecting individual piglets and if it is shown to be effective, it could offer producers a way forward.

Acknowledgements

Project funding was provided by the US National Pork Board. Strategic funding to the Prairie Swine Centre is provided by Sask Pork, Alberta Pork and the Manitoba Pork Council.

March 2013