Farm animal dermatology Flashcards
Dermatological disease, Teat surgery
What would you differential diagnoses be if presented with a group of cows showing the following clinical signs?
- All affected animals are pyrexic
- Recumbent heifers dyspnoeic, swollen muzzles and nostrils, seroud oronasal discharge
- Marked skin tent
- Generalised erythema and alopecaiaon white haired areas
- Ingestion of toxins
- Bluetongue
- Vasculitis
- Foot and mouth disease
Describe the appearance of photosensitisation in cows
- Can be primary or secondary
- Erythema on white areas
- Tachycardia
- Dyspnoea
- Oculonasal discharge
- Secondary: icterus, depression, other behavioural changes
What can cause photosensitisation in cows?
Ingestion of toxins, anything affecting liver function preventing ability to excrete harmful compounds
Describe the mechanisms of action of ragwort toxicity
- Toxin is pyrrolizidine alkaloid
- Converted to toxic intermediates pyrroles and their esters
- Cause damage to hepatocytes
Explain the pathogenesis of photosensitisation skin lesions due to ingestion of toxic compounds causing liver damage
- Liver non-functional so toxic compounds build up in blood
- Reach skin, react with sunlight leading to photosensitisation
What diagnostic tests should be carried out if are suspicious of photosensitisation as a consequence of liver damage?
- Blood sample to assess liver function (serum biochem for liver enzymes)
- Ultrasonography
- Biopsy of liver
Compare the bilirubin and bile acid concentrations in primary photosensitisation vs ragwort poisoning
- Would be normal in primary photosensitisation
- Elevated in ragwort poisoning
What features may be identified on liver biopsy in the case of ragwort poisoning?
Megalocytosis, biliohyperplasia and fibrosis
Outline a treatment plan for cattle suffering ragwort toxicity
- No corrective treatment for liver damage
- Supportive treatment
- Small frequent meals 6x/day
- Oral or parenteral B vitamins
- Fluids
- Euthanasia
What dietary management is appropriate in secondary photosensitisation?
- Low protein, high energy diet
- Rich in branched chain amino acids
If all liver values are normal in a ruminant with photosensitisation, what does this indicate?
That this is primary photosensitisation and no evidence of liver damage
Outline the potential causative agents of primary photosensitisation in cattle
- Diet
- Inherited defect in animal’s metabolism of red blood cells
- Ingestion of lush green plants containing photodynamic compounds e.g. St, John’s wort, clover
What is the prognosis for a cow with primary photosensitisation as a consequence of St John’s Wort ingestion?
Can recover, but if caught too late can be fatal
Give the methods of restraint that can be used for cow in order to examine the udder
- Lifting back leg
- Tail jack
- Tie back leg
- Kickbar (usually ineffective)
- Crush/WOPA box/parlour
List the methods for providing anaesthesia to a teat in cows
- Teat cistern infusion
- Ring-block
- Paravertebral nerve block
- Lumbosacral epidural
- Line block
- Topical (splash) application
Describe the method for a teat cistern infusion and state what is anaesthetised by this method
- 5-10ml of local anaesthetic via teat canal into teat cistern
- Blocks mucosal layer of teat but NOT connective tissue or muscle
Describe the method for a ring block to anaesthetise a cow’s teat and state which structures are anaesthetised by this method
- Inject local anaesthetic in a ring pattern around the base of the teat, full thickness
- Blocks mucosa and connective tissue
Why would you want to avoid using procaine for tea surgery?
Procaine always comes with adrenaline in the UK and and to avoid the vasoconstrictive effect this would have as this could present a risk for necrosis of the teat
What is blocked by a paraveertebral nerve block?
Cranial udder and teats (used for standing surgery)
What is blocked by a lumbosacral epidural and how must surgery using this technique be performed?
- Anaesthesia of caudal abdominal wall up to level of umbilicus, with temporary dysfunction of the hindlimbs
- Need sedation and lateral recumbency for surgery
Describe the method for a line block for teat surgery and outline the key risks
- Give multiple subcut infiltrative injections of local anaesthetic 0.5-cm apart at wound edge to required depth
- Risk of oedema and haemorrhage delaying wound healing, but technique is quick and easy
Describe the method and main advantage of a topical (splash) application of local anaesthetic for teat surgery
- Drip or splash LA onto surgical wound and allow ~20mins contact time for it to take effect
- Can be used before infiltrative anaesthesia in fractious animals
Discuss the use of bandages in teat repair
- Applied to keep teat clean
- Rarely used
- May want to use after surgical repair
What is the main indication for use of staples in teat repair? Advantages and disadvantages
- Superficial wounds only
- If laceration is affecting teat canal may end up with fistulas
- But are quick and cheap
What is the main indication for the use of self-retaining cannulas/milk catheters?
To allow drainage of milk from a teat where milking is not possible e.g. due to full thickness perforated lesion. Milk drips out slowly
What are the main risks with self-retaining cannulas/milk catheters?
- End of cannula is always open and can introduce infection (unless place bung)
- Plug replacement often forgotten after allowing udder to drain
- Total cannula falls out or accidentally left open, both present risk for infection
Briefly describe the closure of teat lacerations
- Need to close each layer individually i.e. submucosal, then connective tissue, then muscle, then skin
- Cannot be milked while wound heals
When is teat amputation indicated and why?
- Where more than 3/4 of the teat has ripped off
- Repair would leave too much scar tissue, which would affect milk flow and increasing the risk of chronic infection
What is a good prognostic factor for teat amputation?
If can perform surgery within 4 hours of injury occurring then good, if overnight then poor prognosis
What is the main risk when performing a teat amputation?
Go too high into venous plexus - may bleed a lot but not too much of a worry, will need antibiotics
What are the methods available for the removal of teat granulomas, and ourline the surgical requirements?
For all methods require local block
- Hudon’s teat spiral
- Alligator forceps
- Theloscopy
Describe the cause and consequences of a teat pea/granuloma
- Unsure of cause, may be infection, haematoma, calculi, papilloma
- Slows milking
Discuss the use of Hudson’s teat spiral for the removal of teat granulomas (advantages, disadvantages)
- Difficult to use
- Insert spiral via streak canal, take pea into spiral and remove pea
- Likely to be painful, requires anaesthetic
- Likely to cause damage to teat sphincter which increases risk of mastitis due to improper closure following milking
Discuss the use of alligator forceps for the removal of teat granulomas
- Easier than Hudson’s teat spiral
- But risk of sphincter damage
Discuss the use of theloscopy for the removal of teat granulomas
- Teat endoscopy, very rare
- Only very valuable cows
- Incision on side of teat, use endoscope to remove pea via the side of the teat
Discuss the use of teat knives (aim, method, risks, post-procedural requirements)
- Used to “repair” hard milkers or teat spiders
- Causes damage to teat canal
- Aim to speed up milking
- Insert knife into base of teat and make incision, rotate 90degrees and made a second incision
- Can be effective
- Ensure keep milking cow to keep incision open
- High risk of infection, bigger problem than slow milking quarter…
What is the legislation regarding chemical anaesthetic in the disbudding of cows?
- Must use chemical anaesthetic other than when chemical cauterisation is used
- Chemical cauterisation only in first week of life
When should dehorning be avoided and why?
Avoid in summer due to high risk of fly strike and infection from flies
Outline the options for restraint for dehorning in cattle
- Good quality crush
- Halter +/- bulldogs
- Light sedation with xylazine/detomidine in fractious animals
- Heavy sedation with the above to induce recumbency if no crush available or very fractious animal
Outline the anaesthesia and analgesia used in dehorning of cattle
- Cornual nerve block
- Local block of subcutaneous branches of second cervical nerve
- Allow time for anaesthesia to take effect (at least 10 mins)
- Pain difficult to control in dehorning
- Check by pricking around horn base with needle
- NSAIDs
Identify the methods for dehorning cattle
- Remove horn close to/flush with skull
- Scoop/gouge dehorners
- Shears/guillotines
- Embryotomy wite
- Bone saw
Give the advantages and disadvantages of scoop/gouge dehorners
- E.g. Barnes dehorners Advantages: - Good for smaller horns - Quick for small to medium/large horns Available in variety of sizes
Disadvantages
- Cumbersome
- Require some strength to operate
Give the advantages and disadvantages of shears/guillotine dehorners
Advantages:
- Quick
- Can be sued for small to very large horns quickly and cleanly
Disadvantages
- Require considerable strenght
- Cumbersome
- Require long arms and lots of room
- Anecdotally can fracture frontal bone in large animals
Give the advantages and disadvantages of using embryotomy wire for dehorning cattle
Advantages:
- Better haemostasis once hot
- Less strength required
Disadvantages
- Slow, stamina required
- Tiring
Give the advantages and disadvantages of bone saws for dehorning cattle
Relatively quick, effective if skilled
Discuss the need for haemostasis in dehorning
- 2-4 large arteries in horns, significant haemorrhage in large horns
- Often less blood with wiring
Describe methods for haemostasis during dehorning of cattle
- Grasp and pull or twist artery slowly with haemostats so they break below bone line and clot (impossible in some cases)
- Work around wound circumferentially with hot iron
- Apply tourniquet around base of horns and poll with baler twine or bands (must be removed after a few days)
Describe the after care following dehorning
- Treat with oxytetracycline spray
- Return to clean environment
- Advise client to check regularly in first 24 hours
- Stress minimised
- Feed from floor not rack to minimise debris into frontal sinus
Outline some common problems and complications that occur as a result of dehorning of adult cattle
- Haemorrhage
- Infection at surgical site (rarely significant problem, manage same as any superficial infection)
- Sinusitis (foreign material into sinuses, some may require systemic treatment and potential trephination of sinus)
- Fly strike
Where should ear tags be placed in cattle?
- Between the 2 cartilage ribs that run length of ear
- In middle third of ear
- Metal tags on proximal border of ear in its middle third
What information is given by the primary and management ear tags?
- Primary: identifies animal, herd, country of origin
- Management: identifies bull and dam of cow and DOB, handwritten, can be coloured
What are common problems associated with ear tags in cattle?
- Infection
- Trauma
Outline the treatment of infection at ear tag sites in cattle
- Lance, clean with antibacterial washes
- Apply topical antibiotics e.g oxytetracycline spray
- In bad cases administer broad spec antibiotics
- Remove tag in severe cases
Outline the treatment for trauma at ear tag sites in cattle
- Often not necessary
- Clean with antibacterials
- Clamp/tie off vessels, compress with bandage
- treat infection
- Surgical repair possible for aesthetic purposes but not required
Outline the procedure for cosmetic dehorning
- Rare
- GA or sedation + local
- Aseptic prep and procedure
- Clip and clean
- Incise and reflect skin around horns
- Dehorn and close skin with sutures to achieve primary healing
Outline the procedure for dehorning goats
- Disbudding kids more complicated than calves
- Use GA - ketamine + NSAID
- Remove bud using forceps once cut awau rather than scoop out with disbudding iron
Why is disbudding kids more risky than disbudding calves?
- Skulls more fragile
- Higher risk of thermal injury to brain
When is it best to nose-ring bulls?
Between 6-12 months
Outline the requirements regarding nose ringing bulls
- Ideal in all adult bulls to aid safe handling
- Legal requirement for all bulls on public footpaths
Outline the restraint for nose ringing bulls
- Crush or suitable stanchion
- Halter +/- nose tongs
- Light sedation with xylazine/detomidine for fractious animals
- Heavy sedation with same in very fractious animals
- Good restraint needed, high risk of being hit by poll
Describe the anaesthesia use for nose ringing bulls
- Local infiltration of septum with procaine theoretically possible but practically difficult
- May not need local anaesthetic if smooth quick administration
- Can soak cotton wool in procaine and hold against septum, but takes long time
Identify the techniques for nose ringing cattle
- Ring placed through soft tissue of nasal septum in front of cartilage
- Nose punch to cut out circular punch of tissue
- Sharp end of ring driven through septum by hand
- Sharp end of ring driven through septum using specific applicator
- Scalpel blade 11 used to cut slit through which ring is passed
Outline the post-nose-ring application requirements
- Must allow to heal before ring is used to restrain the animal
- Should not be used as main method for tying up bull
- If ring is ripped out and cannot be replaced, can stitch up or allow to heal by secondary intention, but cannot be kept on public footpath
