PAIN RELIEF APPROACH TO CATTLE

There are many publications that have attempted to establish cattle pain response for various procedures. There are also journal papers that assess farmers’and vets’attitudes to pain control and measurement of the longerterm benefits of using pain relief in cattle of different ages.

This article aims to provide an overview of pain management methods available to practitioners and, in particular, promote an approach to multimodal pain relief.

Failure to adequately manage pain in cattle can have the following effects:

• delayed healing;

• weight loss or reduced daily liveweight gain;

• decreased productivity;

• impaired cardiovascular and respiratory functions;

• development of aggressive or violent behaviour; and

• adaptive postural changes, which can lead to permanent muscle atrophy and joint degeneration.

Off-licence drug use

When treating food-producing animals, vets may only use medicines containing ingredients authorised for use in such animals. Drugs that have market authorisation (MA) for use in food animals are assigned to annexes one to three.

The annex system is a way of safeguarding public health by preventing human exposure to potentially dangerous or toxic substances. It should be noted that horses are classed as food-producing animals unless their passports are specifically marked as not intended for human consumption.

• Annex 1. Drugs with established maximum residue limits (MRLs). Therefore, withdrawal times can be derived.

• Annex 2. Drugs that do not need to have MRL values determined for the protection of public health.

• Annex 3. Drugs with provisional MRLs. The residues at the proposed levels should not be hazardous to consumer health.

• Annex 4. Drugs with no established MRLs, because their presence at any level in foodstuffs of animal origin would pose a hazard to consumer health.

Therefore, it should be noted that in food-producing animals there is a need to satisfy the requirements of the annex system in addition to the use of drugs under the veterinary cascade. The off-licence use of medicines under the cascade system results in the application of minimum standard withdrawal times, which are 28 days for meat and seven days for milk and eggs.

A veterinary medicinal product can only be authorised in a food-producing species if an MRL has been established, and must be done in advance for all pharmacologically active substances used in the concerned species. For an up-to-date list of authorised veterinary medicines, visit:

• European Medicines Agency (www.emea.europa.eu/index/indexv1.htm);

• www.vmd.gov.uk/General/VMR/VMG07notes.htm;

• www.vmd.gov.uk/publications/consultations/VMR08/VMGN15.pdf; or see

• EC regulation 1950/2006 (drugs authorised for use in equine anaesthesia).

NSAIDs

This drug group possesses the following properties:

• anti-inflammatory;

• antipyretic;

• analgesic; and

• antiendotoxic.

Situations in which NSAIDs would be contraindicated include hypovolaemia, renal disease and gastrointestinal ulceration. They should not be used in conjunction with steroids, due to the additive effect on the gastrointestinal tract, which can lead to ulceration.

Corticosteroids

The only corticosteroid licensed for use in cattle is dexamethasone. There are several different products available with differing formulations – offering various durations of antiinflammatory activity. Contraindications include renal disease, congestive heart disease and viraemia. Corticosteroids can be used to induce parturition, and should be used with caution in pregnant animals. Corticosteroids can also delay wound healing and have immunosuppressive activity, therefore, they should be avoided prior to surgery and given where appropriate with an antibacterial agent.

Opioids

Opioids, such as morphine or butorphanol, offer the most potent analgesic properties of drugs available to veterinary surgeons. However, there are no licensed products available for use in cattle, therefore restricting their use considerably. Butorphanol can be used at a dose of 0.05-0.1mg/kg IM or IV and is suitable for multimodal analgesia – for example, combined with NSAIDs.

There are two products licensed for use in horses for human consumption:

• torbugesic (equine meat withdrawal nil); and

• dorulex (equine meat withdrawal nil).

In other species, the drug is licensed as an analgesic for moderate to severe pain with post-surgery indications.

• Alpha 2 agonists

These drugs are sedative agents commonly used in all species. They have some analgesic and muscle relaxant properties. For several years the only available licensed drug in cattle was xylazine – this has now been joined by detomidine to offer an alternative depth and duration of sedation.

There are currently no other licensed sedative drugs (or indeed general anaesthetic agents) for use in cattle entering the food chain. Dose-dependent side effects include decreased GI motility and decreased cardiorespiratory function.

Local anaesthetics

Local anaesthetic drugs provide temporary alleviation from pain by the inhibition of sensory receptors when used as locally infiltrative or perineural techniques. They can also be used in many different locations via an intravenous regional perfusion technique, and are, therefore, most useful when the anaesthesia of a specific area is required for surgery.

A full description of all the local anaesthetic techniques available to cattle practitioners is beyond the scope of this article, but a brief overview of the commonly encountered techniques will be provided.

Licensed products in cattle include:

• Willcain (Dechra). Procaine and adrenaline. Licensed for disbudding and dehorning procedures. Two to 5ml SC. Meat/milk withdrawal nil.

• Adrenacaine (Norbrook). Procaine and adrenaline. Licensed for disbudding and dehorning procedures. Two to 5ml SC. Meat/milk withdrawal nil.

Commonly encountered local anaesthetic techniques that farm animal vets should be familiar with are:

• line block;

• inverted L-block;

• ring block;

• intratesticular injection;

• intravenous regional anaesthesia (IVRA);

• caudal epidural;

• retrobulbar;

• auriculopalpebral; and

• infraorbital.

• Line block

– Uses. Non-specific regional infiltrative anaesthetic technique, for example, in flank or eyelid.

– Technique. Multiple subcutaneous/intramuscular injections of local anaesthetic 1-2cm apart. Infiltrate to the depth required.

– Needle/volume. Twenty gauge, 2.5cm. Volume depending on block required.

– Advantages. Easy.

– Disadvantages. Oedema and haematoma at incision site may delay wound healing (clip and clean thoroughly prior to block). Deeper layers of abdominal wall may have incomplete analgesia and muscle relaxation. Large volume required (potential toxicity).

• Inverted L-block

– Uses. Another non-specific regional anaesthetic technique. Flank anaesthesia predominantly, for example, LDA surgery, caesarean section.

– Technique. Block the nerves from T13-L4 in an inverted L outline using the technique for a line block.

– Needle/volume. Twenty gauge, 2.5cm. Approximately 100ml, but depends on the length of block required.

– Advantages. Easy, anaesthetic away from incision.

– Disadvantages. Deeper layers of abdominal wall may have incomplete analgesia and muscle relaxation. Large volume required (potential toxicity).

• Ring block

– Uses. Teat surgery, distal limb surgery.

– Technique. Local anaesthetic is instilled in a line block encircling above the area to be desensitised.

– Needle/volume. Eighteen or 20 gauge, 1-2in, 10-30ml, depending on site.

– Advantages. Straightforward.

– Disadvantages. Small risk of ischaemia.

• Intratesticular injection

– Uses. Castration.

– Technique. Local anaesthetic is injected into the body of the testicle with a bleb under the scrotal skin. This is repeated in the other testicle – either by redirecting the needle beneath the first testicle across to the second or via a second injection. An alternative technique is to inject into the vessel in the spermatic cord.

– Needle/volume. Nineteen or 20 gauge, 2-3cm, 5-10ml each side, depending on size.

– Advantages. Simple to perform.

– Disadvantages. Requires adequate restraint – normal testicular anatomy can be distorted by the local infiltration.

• Intravenous regional anaesthesia (IVRA)

– Uses. Surgery of the distal limb

– for example, digit amputation or interdigital fibroma removal.

– Technique. Restrain the animal in a crush or wopa box. Place a tourniquet above the area to be blocked; this can be a piece of bicycle tyre rubber, IV drip line or flutter valve pipe (the leg restraint on a crush is often inadequate as a tourniquet if the animal moves). Inject local anaesthetic into a vein distal to the tourniquet.

The block will provide analgesia while the tourniquet remains in place. The last place to desensitise is the interdigital space. The limb can be exsanguinated using an Esmarch’s bandage to prevent blood contaminating the operating site.

– Needle/volume. Nineteen gauge, 1.5in, 20-30ml.

– Advantages. Simple, safe, reduced bleeding (tourniquet), single injection, quick.

– Disadvantages. It is not always successful. Adequate restraint is required.

• Caudal epidural

– Uses. Obstetrical procedures – for example, dystocia, uterine/vaginal/rectal prolapse. Castration, tail surgery.

– Technique. Commonly at Co1-Co2, but could be at S5-Co1. The joint between Co1 and Co2 is the most movable joint when pumping the tail up and down.

– The technique in sheep is more difficult than cattle. The point of the needle is placed in the centre of the depression and advanced cranially and ventrally at 15° to the vertical. The needle is advanced until it contacts the ventral floor of the vertebral canal, then withdrawn approximately 0.5cm.

Confirm placement by hanging drop technique (subatmospheric pressure aspirates a few drops of local).

The epidural space is beneath the ligamentum flavum and above the dura matter. The dural sac ends at L7 in cattle, S3 in sheep, L6-7 in dogs, L7-S3 in cats and mid-sacrum in horses. No resistance to the injection should be encountered (using the hanging drop technique with a drop of saline in the needle hub

– the negative pressure in the epidural space should suck in the saline). Maximum effect after 10-15 minutes; it lasts one hour.

– Needle/volume. Cattle: 19 gauge 1.5in needle, 1.0ml/100kg local (reduce for Belgian blue breeds and blue cross, due to their smaller epidural space). Sheep: 19-gauge, one inch needle, 1.5-2ml local. Maximum 1.0ml/50kg.

– Advantages. Simple and inexpensive.

– Disadvantages. Risk of postural instability/recumbency, haemorrhage due to puncture of venous sinus.

• Cornual

– Uses. Dehorning, disbudding.

– Technique. Desensitise corneal branch of lacrimal nerve (part of ophthalmic division of trigeminal). Lateral ridge of frontal bone, along from lateral canthus of eye, slightly closer to horn than midway along frontal ridge. Depth is 1.0cm in young calves to 2.5cm in large bulls. Do not insert too deeply; keep needle parallel to skin surface. The cornual artery and vein are close to nerve, so aspirate first. Adequate block can be confirmed by blink response during infiltration and ipsilateral ptosis.

Large bulls may have innervation to the horn from subcutaneous branches of the second cervical nerve requiring infiltration of local anaesthetic along the caudal aspect of the horn.

– Needle/volume. Twenty gauge 2.5cm, 5-10ml.

• Retrobulbar

– Uses. Enucleation.

– Technique. Sedated, well restrained animal. Use an index finger to deflct the globe and protect it from needle point. Introduce needle through eyelid at orbital rim and penetrate at dorsal, ventral, medial and lateral aspects. Inject 15-20ml local at increments during needle advancement. Blocks optic nerve, oculomotor nerve, trochlear nerve, trigeminal nerve, abducent nerve and facial nerve.

– Needle/volume. Nineteen gauge, 3.5in bent to form a loop, 50-60ml.

– Advantages. Easier to perform than other techniques.

– Disadvantages. Risk of penetration of globe, orbital haemorrhage, damage to optic nerve, injection into optic nerve meninges, oculocardiac reflex (dysrhythmias) due to manipulation of the eyeball.

• Auriculopalpebral

– Uses. Paralysis of the eyelids (without analgesia) – for example, examination of the eye, injecting medication or procedures of the eye when combined with sensory anaesthesia.

– Technique. Palpate nerve in a notch on the zygomatic arch anterior to the base of the auricular muscles.

– Needle/volume. Twenty gauge, 2.5cm, 5-10ml.

• Infraorbital

– Uses. Insertion of nose rings in bulls, repair of nasal lacerations (nerve is continuation of maxiallary branch of CN5, sensory only).

– Technique. Foramen of infraorbital canal is located rostral to the facial tuberosity on a line extending from the nasomaxillary notch to the second upper molar tooth. Needle is inserted deep to the levator nasolabialis muscle. Nerve is difficult to palpate.

– Needle/volume. Eighteen gauge, 3.75cm, 20-25ml.

Other techniques

Compassionate nursing care of the patient plays an important part in pain management. Basic points to remind farmers are:

• provision of food and water,

• comfortable walking and lying surfaces;

• positioning the animal away from extremes of weather;

• dry, clean bedding where appropriate; and

• patience when moving animals that are uncomfortable and slow.

Additional therapy includes the following treatments.

• Foot blocks. These should be applied to the sound claw, and will alleviate pain by reducing the weight bearing on affected claws. Blocks are useful when cattle are on a firm, walking surface – whether inside or out – but make little difference when the foot can sink into the ground surface, such as on soft ground or a deep straw bed.

Blocks are also useful to confirm that a foot lesion only affects one claw by producing a much improved gait when the sound claw is weight bearing – particularly when a salvage technique, such as digit amputation, may be required.

• Mucolytics. Includes Bisolvon (active ingredient bromhexine, Boehringer Ingelheim). These are useful to alleviate discomfort from excess mucus build up in severe cases of respiratory disease as an adjunct to therapy.

• Diuretics. Diuretics, such as frusemide – for example, Dimazon (Intervet/Schering-Plough) are licensed to remove mammary and limb oedema, as well as oedema associated with cardiorespiratory disease and trauma.

• Antispasmodics. Includes Buscopan (active ingredients butylscopolamine and metamizole, Boehringer Ingelheim). These can be used for spasmodic colic and diarrhoea, as well as for muscle relaxation – to aid the passage of a stomach tube or urinary catheter – and to reduce the pain and likelihood of stricture formation during oesophageal foreign body removal.

Summary

There are several methods available to the practitioner to provide pain relief in cattle.

Farmers should be encouraged to play an active role in pain management in their stock, and the veterinary surgery can add to this in many circumstances, using a combination of the methods described.