Designed to make mechanical threshold testing on animals as easy and accurate as possible. Uniquely, the measurement head sits on a cushion of air.
For handheld testing, unlike humans, animals don’t keep still and movement can affect the data from traditional dial and force sensors. In the Prod range, the air cushion absorbs any movement without distorting the threshold force reading.
Extensively validated, used globally with dogs, cats, rabbits, chickens, pigs, sheep, horses, donkeys and cows and cited in many research publications. The PROD (Pressure Rate Onset Device) is easy to use: as soon as tissue pressure is detected, the red and green guide bars activate, teaching you to increase the pressure at a constant, preset rate: press too hard and the red bar shows; press too little and the green bar shows. With a little practice, it is easy to apply a repeatable force at a known rate – an important point for publication. There are no buttons to press – just touch the probe against the subject and the guide bars prompt you to increase the pressure at a controlled rate. At threshold, simply withdraw the Prod; the peak reading of force is stored and displayed automatically in Newtons.
The Prod incorporates a peak-hold facility: the highest reading of force since the reset button was last pressed is retained and displayed. This is preferable to retaining just the last reading at a movement response as this may momentarily decrease the detected force.
The Prod is small, dark-coloured and has no trailing leads. This allows “non scary” application – very important for a behavioural response. The instrument fits the palm of the hand allowing even prey species to be approached. A horse won’t mistake the Prod for a worming syringe!
Use of hand held algometry is now widely accepted as Routine Veterinary Practice for clinical pain management and clinical studies. This applies particularly in post operative pain assessment and monitoring chronic pain treatment as in osteoarthritis.
Every Prod Algometer is calibrated in a measurement fixture against a reference force transducer. But we then also test the Prod, hand held, at strange angles and with a deliberately shaking hand, against the reference to ensure that the device will still measure properly under real life conditions when working with animals.
The Prod range of algometers
pressure = force/area
Force range and tip diameter: The Prod can be used to apply forces up to 25N. This is lower than the range of some other algometers because we consider this to be the maximum that can be applied smoothly and repeatably to most conscious animals. For small species even this is too much: 25N would just slide a kitten sideways across the table, and for this reason we always recommend smaller tips rather than more force, with the aim of achieving a baseline that allows headroom either to increase the threshold for an analgesic effect, or to reduce it for hyperalgesia.
1 cm tips are too big: Some publications report using 1cm² tips which results in forces of up to 250N to achieve a response on a horse and, as seen in the graph below, a large spread in the data. Taken from a poster that Topcat presented (ACVA Capetown, 2012) of published papers using instruments of many different force ranges, it reinforces Topcat’s view that forces above 100N are very difficult to apply to an animal in a controlled manner.
Research by Topcat (some of it on ourselves) indicates that tip diameters above 8mm should usually be avoided (as they require large, impractical forces) and that the ideal diameter (for dogs, cats etc) is 2-4mm. Based on extensive experience we now advise a 2mm or 4mm tip for small animals. This is discussed in more detail here
1 mm tips are available for cattle, sheep and other prey species whose natural behaviour pattern is not to show a pain response (as it singles them out as the weak one of the group). The tips are smooth, flat and interchangeable, with an edge radius of 10% of the diameter.
ProdPro is supplied with tips from 1-8mm and an extension piece for probing soft tissue.
Technical specification:
- Force range: 0.5-25N
- Accuracy: ±0.5N Weight: 260g
- Battery life: 10 hours on 1 PP3 (not supplied)
Key features of the Prod algometer range:
- Designed specifically for animal testing
- “Soft” measurement head with air cushion
- Self-contained and easy to hold (no trailing leads)
- “Non-scary” to animals
- Realistic force range for testers to apply
- Can be used with limb mounted actuators as well
- Range of tips to allow study design for optimal headroom
(both for analgesic effect and for detection of hyperalgesia)
Hand held algometry
The ProdPlus is for hand held manual application and is supplied with 2 Probe tips (usually 2 & 4 mm or 1 & 2 mm). The ProdPro has an axial actuator for hand held use and is also supplied with an interface for driving limb mounted actuators as well as 4 probe tips (1,2,4,8 mm) & one extension piece
An angled actuator is available for both ProdPlus and ProdPro to improve access to restricted stimulation sites.
ProdPlus can be used with an extension pole in wildlife and untamed animals. The pressure line transmits the air pressure back from the actuator to the Prod algometer, allowing the force to be applied sensitively without endangering the measurement unit. The system can even be used with cattle in a crush with the longer extension piece shown here.
Remote limb actuators
Regular mechanical nociceptive threshold testing using the same pneumatic actuators via more distant control enables testing under considerably more natural conditions than with hand held algometry when the tester must approach the animal. The limb actuator is attached to the leg with a boot or band and the animal usually quickly acclimates to wearing the set (with a dummy on the contra-lateral limb); only a lightweight, flexible tube connects to the ProdPro (held by the tester or placed on a bench). Unknown to the animal, the stimulus is applied by depressing a syringe to pressurise the line and the behavioural response is not influenced by the need to approach the subject.
The peak hold facility is of particular benefit as, when the animal lifts its leg at the threshold response, the tendon behind the canon bone relaxes and up to 20% of the force reading can be lost as slack in the mounting strap. The effect, we have found, is most noticeable with horses.
A wireless mechanical system WMT1 is available for large animals and is controlled remotely in the same way as the Topcat wireless thermal systems. Pressure to drive the same limb actuators is supplied from a rechargeable syringe mounted on the animal’s back alongside the control unit. The system is unsuited for species below around 60 kg due to the need for this pressurised air supply. It has been used to date primarily on horses and camels. The wireless mechanical and thermal systems can be used together on one animal, providing data from both modalities in a single study.