Dehorning Flashcards
Innervation of the horns in cattle and small ruminants
Cattle - cornual nerve - a branch of the zygomaticotemporal nerve (trigeminal)
Additional sensation may be present caudally from branches of C2
A small proportion will be innervated by the frontal nerve - this is not possible to block
Goats - in addition to the cornual nerve, sensation is provided by the infratrochlear nerve located close to the dorsomedial margin of the orbit
Nerve blocks for dehorning in cattle
The cornual nerve is blocked, a branch of the zygomaticotemporal nerve, which is part of the trigeminal nerve.
The cornual nerve is often palpable along the ventrolateral aspect of the frontal ridge, halfway between the lateral canthus of the eye and the base of the horn
Use 20g 1-1.5” needle just under the frontal ridge and 5-10ml local
Older animals may also require hemicircumferential infiltration of the caudal aspect of the horn base to anesthetise cutaneous branches that originate in the second cervical spinal nerve
Nerve blocks for dehorning goats
- The cornual branch of the lacrimal nerve (zygomatico–temporal) is blocked behind the root of the supraorbital process. The needle is inserted to a depth of 1–1.5 cm, and as close as possible to the root of the supraorbital process.
- The cornual branch of the infratrochlear nerve is at the dorsomedial margin of the orbit and is generally palpable. The needle is inserted close to the margin of the orbit to a depth of about 0.5 cm.
V sensitive to local - do NOT exceed the toxic dose of lignocaine = 8mg/kg and for procaine 20mg/ kg.
NB procaine only labelled LA for food producing animals in UK. Lido used rutinely in US
what age does the horn bud attach to the skull in cattle?
Approx 2 months
when the continuing outgrowth of the cornual process of the frontal bone connects to the horn bud
Label the diagram
From what age does the frontal sinus open into the horn in cattle?
Approx 4-6mo
Give 4 methods available for dehorning cattle
1) Caustic paste - Na, K or Ca hydroxide. Done as soon as horn buds appear; 3-7d. Does cause some discomfort but not legally req to give NSAID if <7d old in UJ
2) Thermal - butane powered burning irons that operate approx 500-600°C. Can do from 3d to 2mo (has to fit entire horn bud over it)
3) Sharp/cutting -
a) Tube dehorner: circular cut when twisted over the base of a horn bud on young calves then a twist upward scoops out the horn. Haem is minimal
b) Scoop/Gouge dehorner: used on calves from 3 months to 1 year+, as long as the dehorner fits over the base of the horn enough to remove a 1-cm ring of skin. Exposed arteries are pulled and snapped so they recoil under the skin where they can clot. Can apply thermal dehorner to control haem after. Opening to the sinus typically left open
c) Keystone: large cutting instrument with 2 opposing blades on long handles. Haemostasis similar to above or can apply tourniquet around the poll for a few days
d) Obstetric Wire: will not work for really large horns occasionally found on cows and bulls and horn regrowth that curves into the head. Essential to include a 1cm ring of haired skin with the horn. Relatively slow
4) Genetic - Angus & polled Herefords
Label the instruments
Keystone (top)
Roberts (left)
Barnes (right)
Describe the procedure for ‘cosmetic’ dehorning
elliptical incisions leaving no more than a 1-cm margin around the base of the horn beginning 5 to 7 cm dorsal to and ending 5 to 7 cm ventral to the base of the horn
Skin dissected away ensuring not to transect the auricular muscles of the area
Ob wire is placed in the ventral incision against the frontal bone with the wire directed toward the poll and used to saw off the horn
The incised skin is undermined if necessary and brought into direct apposition by using #2 nonabsorbable sutures in a simple interrupted or mattress pattern.
NSAIDs indicated
Complications:
Haemorrhage is the most common PO complication - artery to be pulled or ligated where possible, or a tourniquet can be applied
Infection - can lead to sinusitis requiring trephination/lavage
Skull fractures can also be a complication
Possible complications of dehorning.
Why are goats more susceptible to severe complications>
Meningitis (esp thermal dehorning)
Sinusitis
Goats have thin frontal bones so cerebral thermal damage more common
Goats also have larger horns relative to the size of the head vs cattle, horns are in parietal position therefore closer together vs cattle (temporal) - so larger incisions closer together so harder to close in goats vs cattle.
Overall complication rate 39% (Hartnak VS 2018) - main risk factor for complications was increasing weight of the goat. Complications much lower for disbudding at a young age vs dehorning older.
Hempsted TVJ 2018
What were the main complications folowing disbudding in goats via thermal, chemical and cryosurgical methods?
PO pain seen in all - less for thermal vs cryo & caustic
Higher incidence of brain injury with thermal cautery - 10/70. This was not seen w other tx, but no sig diff in ave daily gain between groups.
