| Line 1: |
Line 1: |
| | {{review}} | | {{review}} |
| | | | |
| − | ==Minimizing the potential problems of a wound==
| + | In clinical practice healing can be achieved in one of three ways: |
| − | [[Image:Acute wound protocol.jpg|right|thumb|250px|<small><center>Veterinary protocol for management of the acute wound (Image courtesy of [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary])</center></small>]]
| + | * Primary or first intention healing. |
| − | ‘Time spent in the preparation of a wound is never wasted’ – Barrie Edwards, 1984
| + | * Secondary or second intention healing. |
| | + | * Delayed primary healing. |
| | | | |
| − | Harmful effects can be minimised by careful wound management and sound
| + | ==Primary or first intention healing== |
| − | surgical techniques including:
| |
| | | | |
| − | # Early intervention
| + | This is the mechanism that occurs when the edges of a wound can be closely |
| − | #* Bacterial adhesion occurs around four to eight hours after wounding and therefore intervention before this occurs provides a much cleaner wound
| + | apposed. Most surgical wounds rely upon this mechanism. In a non-infected |
| − | #* Long delays in attention to a wound inevitably result in overt infection and contamination by foreign matter
| + | surgical wound, healing is reliably accomplished in a predictably short time |
| − | #* Delay in wound examination may, however, make recognition of nonviable tissue easier
| + | (usually 7 to 14 days). |
| − | # The application of sound surgical principles
| |
| − | #* The use of appropriate debridement techniques
| |
| − | #* The use of suitably placed surgical drains - vacuum drains and Penrose (capillary) drains
| |
| − | #* Minimizing dead space within the wound itself
| |
| − | # The use of physiologically sound wound lavage mechanisms (see [[Wound Management Basics - Donkey#2. Initial cleaning|Initial cleaning below]] and [[Wound Healing Inhibition Factors - Donkey#Foreign body|Foreign body]]).
| |
| − | # [[Wound Management Basics - Donkey#5. Infection control|Reducing and controlling infection]]
| |
| − | # [[Wound Management Basics - Donkey#4. Prevention of further injury and contamination|Eliminating and preventing contamination and continuing trauma]]
| |
| | | | |
| − | ==Summary==
| + | Elective surgical wounds are probably the current ‘gold standard’ of |
| − | Recognition of potential problems, that is, factors that might inhibit wound
| + | wound management, but there are major differences between surgical |
| − | healing (see [[Healing Fundamentals - Donkey#Delayed primary healing|Delayed primary healing]]), allows decisions on the best or most appropriate
| + | wounds and accidental injuries (see Table 1 and Table 2 below) and so there are |
| − | management and the likely results of healing. Owner and veterinary
| + | almost inevitable differences in healing between the surgical situation and |
| − | expectations can be rationalized and explained.
| + | the accidental wound. |
| − | Consideration of the problems from the outset will almost always result
| + | [[Image:Wounds table.jpg|center|thumb|450px|<small><center>(Image courtesy of [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary])</center></small>]] |
| − | in earlier and more satisfactory healing. | + | [[Image:Table healing.jpg|center|thumb|450px|<small><center>(Image courtesy of [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary])</center></small>]] |
| − | By the nature of their location and severity, many wounds will have
| |
| − | particular limitations and needs, and these must be addressed from the
| |
| − | outset of wound management.
| |
| − | All wounds must be promptly and thoroughly examined to establish
| |
| − | the full extent of the damage. It will usually be difficult to perform a full
| |
| − | examination on a wound without appropriate sedation (or, if necessary,
| |
| − | anaesthesia). The exact site, depth and direction of the wound are critical
| |
| − | factors in all wound management procedures.
| |
| − | The cause of the wound and the time delay between injury and veterinary
| |
| − | attention will have important implications for the subsequent management.
| |
| − | The tetanus vaccination status should always be determined and | |
| − | appropriate protection ensured.
| |
| − | [[Sedatives and Tranquilisers|Sedatives]], [[Opioids|opioid analgesics]] with [[NSAIDs|non-steroidal anti-inflammatory drugs]] | |
| − | make initial assessment and subsequent procedures far easier.
| |
| | | | |
| − | ==Initial procedures==
| + | In primary wound healing, the various tissue structures involved are |
| | + | managed by suturing to restore very close normal anatomical relations. The |
| | + | underlying tissues are closed carefully to minimize dead space, provide good |
| | + | support for the skin wound itself and to restore function as far as possible. |
| | + | Although in most cases this will involve closure of the wound by sutures |
| | + | or staples, this is not a prerequisite. Close apposition of the margins of the |
| | + | wound using adhesive tabs or even simply by bandaging in a suitable fashion |
| | + | may have the same effect and may indeed be considered to be advantageous |
| | + | in that there is no foreign matter in the wound. Minimal granulation tissue |
| | + | formation and epithelial migration are required and so the wound heals |
| | + | rapidly. Usually within seven to ten days the wound margin is sufficiently |
| | + | strong to permit removal of skin sutures. |
| | | | |
| − | ===1. Control of haemorrhage===
| + | Few accidental/ traumatic wounds are amenable to this approach because |
| | + | there are almost always some complicating factors. Where it is possible |
| | + | however to create a ‘surgical’ situation from a traumatic injury, wounds will |
| | + | heal with an excellent result both functionally and cosmetically. |
| | | | |
| − | This is a major initial consideration.
| + | ==Secondary or second intention healing== |
| | | | |
| − | ====Arterial bleeding====
| + | Second intention healing is the natural way for a wound to heal. Wounds |
| | + | too extensive or contaminated to suture, or those in which primary closure |
| | + | has failed, must heal in this way. |
| | | | |
| − | Arterial bleeding is potentially the most dangerous haemorrhage. Even small arteries can produce significant blood loss. This is '''bright red''' and under '''high pressure'''.
| + | In second intention healing, a '''healthy bed of granulation tissue is |
| | + | required before epithelialisation can proceed'''. The quality of the granulation |
| | + | tissue bed and the anatomical site has a strong influence on the rate of |
| | + | healing of the wound. Because there is a necessary delay in the development |
| | + | of the granulation tissue bed, there is an inevitable delay in healing. |
| | | | |
| − | * Control of arterial bleeding is usually effected by application of '''direct pressure over the site''' (or in the arterial tree on the heart side of the injury). This may need to be maintained for up to 10 to 15 minutes
| + | Major factors in the process of second intention healing are the size of |
| − | * Alternatively a '''pressure bandage''' can be applied. It is possibly helpful to use a firm roll of bandage over the actual site to increase the local pressure without having to make the bandage dangerously tight for other tissues
| + | the wound, the anatomical location and the extent of '''complicating factors''': |
| − | * Management of pressure bandages is important. If after two hours bleeding is still present when the bandage is removed, an alternative method of haemostasis should be used | + | * Over 70% of donkey wounds are complicated by failure to heal and chronic inflammation |
| | + | * Second intention healing relies upon the inflammatory response; the longer the wound takes to heal, the greater will be the scar and the possible cosmetic and functional deficits |
| | + | * The anticipated problems associated with second intention healing may encourage clinicians to try to close wounds by primary union, although this can be ill-advised |
| | | | |
| − | '''Note:
| + | <u>Most traumatic wounds create circumstances that preclude primary |
| − | * '''Pressure bandages can be catastrophic without the correct bandaging technique. It may stop the bleeding but leave the donkey with extensive skin necrosis or, even worse, tendon necrosis
| + | closure</u> and so second intention healing is a major clinical aspect of wound |
| − | * '''Pressure bandages should not be left on for more than one to two hours
| + | management in donkeys. Factors that disturb normal corrective processes |
| − | * '''Removal of the dressing can reinitiate bleeding
| + | inevitably complicate and delay wound healing. Early recognition of healing |
| | + | difficulties allows prompt correction; ideally factors that will result in |
| | + | non-healing should be recognized pre-emptively at the time of wounding, |
| | + | but inevitably some will not be apparent until later and possibly when the |
| | + | wound has failed to heal. |
| | | | |
| | + | The owner of a donkey with one or more of these factors can be given |
| | + | rational advice on the likely prognosis and the time-scale for healing. Most |
| | + | non-healing wounds are preventable by suitable management in the early |
| | + | stages after injury and others are understandable or predictable. Failure |
| | + | to recognize potential reasons for failure of healing in a fresh wound, or |
| | + | delayed presentation, mean that the wound will become chronically inflamed |
| | + | and so the healing process will be unnecessarily prolonged. |
| | | | |
| − | '''Direct ligation or clamping''' of the bleeding artery is of course an effective
| + | ==Delayed primary healing== |
| − | method of control, but arteries usually run alongside nerves and inadvertent
| |
| − | clamping of the nerve in a conscious donkey will usually cause a dangerous
| |
| − | response. Also, ligation of a major end-artery can be catastrophic. Ligation
| |
| − | of a bleeding artery will also leave a suture in the wound and the material
| |
| − | used must be chosen with care.
| |
| | | | |
| − | ====Venous bleeding====
| + | This is a useful procedure that combines the early stages of second intention |
| | + | healing with a primary intention healing after a few days. It is applicable to |
| | + | a few wounds but it is a very rewarding process. If closure is delayed for |
| | + | 72 to 96 hours, only a minimal risk of infection exists. The method allows |
| | + | contaminated wounds in which immediate closure may lead to infection to |
| | + | heal faster than would be the case for second intention healing. |
| | + | The wound is '''initially cleaned and debrided, but is not closed'''. After a |
| | + | variable time (usually two to four days), the wound is '''surgically debrided to |
| | + | remove any demarcated tissues and closed by suture as for first intention''' |
| | + | healing. There is an inevitable delay in the healing process but, where it |
| | + | is applicable, the healing time is usually shorter than second intention |
| | + | healing. |
| | | | |
| − | Venous bleeding is usually '''dark''' in colour and has a ''''slow flow rate''', although the overall volume can be large if large veins are involved.
| + | The '''clinical advantages'' of delayed primary healing are considerable: |
| | + | * The wound can be assessed for causes of failure of healing at various stages, allowing the best time for closure to be chosen |
| | + | * Acute inflammatory responses and natural debridement can take place before it is ‘driven’ towards healing without the development of a difficult and prolonged chronic inflammatory process |
| | | | |
| − | * Venous bleeding can be controlled by '''direct pressure''', by application of a '''firm (but not tight) bandage''' or by allowing a '''normal clot''' to form in the site
| + | The '''disadvantages''' include the need for repeated procedures and an inevitable increase in scarring when compared to first intention healing, even when the time delay is relatively insignificant. |
| − | * Usually venous bleeding will stop naturally within 10 to 15 minutes. Disruption of the clot may, however, restart the bleeding
| |
| − | | |
| − | ====Capillary bleeding====
| |
| − | | |
| − | Capillary bleeding is '''slow''' and of '''low volume''' but can be '''bright or dark''' in colour. It can be controlled by allowing '''natural clotting''' to take place or by application of '''cold compresses or dressings'''. Capillary ooze
| |
| − | may continue for some time after injury but is unlikely to be of sufficient volume to cause problems.
| |
| − | | |
| − | | |
| − | ===2. Initial cleaning===
| |
| − | | |
| − | The first objective is to '''expose the injury''' so that a thorough assessment | |
| − | can be made. This will always involve '''clipping of the hair''' and '''removal of
| |
| − | gross contamination'''. During this stage the '''wound itself should be covered'''
| |
| − | or filled with an inert, water-soluble jelly such as obstetrical lubricant (K-Y
| |
| − | Jelly) or hydrogel (Intrasite Gel ). This will prevent clipped hair and other
| |
| − | superficial debris from entering the wound during clipping and initial
| |
| − | washing of the surrounding skin.
| |
| − | | |
| − | Once the wound area is clipped and cleaned, the gel within the wound is
| |
| − | washed out with (sterile) saline under minimal pressure (3-5 psi), but (warm)
| |
| − | running water is commonly used until any gross contamination is dislodged.
| |
| − | The '''final wash should be with normal saline to restore physiological status'''.
| |
| − | Care should be taken to ensure that this does not drive foreign matter into
| |
| − | the depths of the wound. If the wound has bled heavily, washing may
| |
| − | loosen the blood clot and restart haemorrhage, which may then need to
| |
| − | be controlled.
| |
| − | | |
| − | A '''solution of 0.5% chlorhexidine''' is a standard wound antiseptic with
| |
| − | minimal harmful effects. It can be used if the wound is heavily contaminated
| |
| − | or is over two to four hours old. Fresh wounds probably do not need an
| |
| − | antiseptic wash.
| |
| − | | |
| − | At this stage the wound can be lavaged with '''warm (sterile) saline''' under
| |
| − | increased pressure (7-10 psi - simply using a 50 ml syringe and squirting the saline directly from it with moderate
| |
| − | pressure can achieve this). Higher pressure can drive bacteria and
| |
| − | particles into the tissues and open fascial planes, while lower pressures may
| |
| − | fail to dislodge foreign matter and bacteria.
| |
| − | | |
| − | '''Avoid'''
| |
| − | * Wiping the wound with dry or saline-soaked swabs that may just push bacteria and foreign matter deeper into the wound
| |
| − | * Strong chemical disinfectants and antiseptics. These should not be used without considerable thought on the possible balance between benefit and harm
| |
| − | | |
| − | ===3. Wound assessment===
| |
| − | | |
| − | The wound must be fully assessed to establish its full extent and the
| |
| − | various structures in the vicinity must be considered individually. A sterile gloved finger is a sensitive and sensible instrument to use! Sedation may be required. Small foreign bodies, bone fragments and tissue damage can be appreciated.
| |
| − | | |
| − | '''Major factors that need to be established in a wound'''
| |
| − | * Depth of the wound
| |
| − | * The direction of the damage
| |
| − | * The extent of the damage
| |
| − | * The precise tissues and structures involved
| |
| − | | |
| − | After assessment, the wound is carefully '''flushed again with sterile saline'''.
| |
| − | The presence of any of the recognized factors that might hinder, [[Healing Fundamentals - Donkey#Delayed primary healing|delay
| |
| − | or prevent healing]] must be recognised early. Where delayed
| |
| − | healing is unavoidable, the owner can be advised accordingly and a suitable
| |
| − | plan instigated to expedite the healing as much as possible without unrealistic
| |
| − | expectations.
| |
| − | | |
| − | ===4. Prevention of further injury and contamination===
| |
| − | | |
| − | A '''hydrogel or sterile water-soluble (obstetrical) lubricant gel''' is packed into
| |
| − | the wound and a suitable protective dressing applied, taking care not to
| |
| − | cause further damage.
| |
| − | | |
| − | ===5. Infection control===
| |
| − | [[Image:Infected wound.jpg|right|thumb|250px|<small><center>Infected wound (note the necrotic tissue which is black or brown in colour whilst the healthy granulation tissue in the lower wound is pink and has a definite epithelial margin). (Image courtesy of [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary])</center></small>]]
| |
| − | '''Up to six to eight hours''' after injury, a wound is usually considered
| |
| − | contaminated and [[Antibiotics|antibiotics]] could be considered to be prophylactic.
| |
| − | '''Beyond six to eight hours''' bacteria have usually become established in the
| |
| − | damaged tissues and the wound is then classified as infected. [[Antibiotics]]
| |
| − | used at this stage are therapeutic. Although this so-called ‘golden period’ is
| |
| − | an important concept, it suffers from being too prescriptive; in some cases
| |
| − | the wound may become infected slower or faster. The overriding principle
| |
| − | of wound management is that the wound should be dealt with as soon as
| |
| − | possible after injury.
| |
| − | | |
| − | [[Antibiotics]] are used to treat known or suspected infections and
| |
| − | as prophylaxis for various types of medical and surgical procedures.
| |
| − | Notwithstanding the consideration of contamination and established
| |
| − | infection, there is merit in administering a full dose of antibiotic before
| |
| − | any interference is undertaken, the wound site covered throughout the
| |
| − | procedure. Topical antibiotics are probably not helpful, but sometimes soluble antibiotic
| |
| − | is usefully added to lavage solutions (especially in special or complicated wounds, such
| |
| − | as wounds involving joints and body cavities).
| |
| − | | |
| − | Failure to control potential and actual infection will inevitably result in retarded healing. Removal of bacteria
| |
| − | before adhesion occurs is a useful aid to wound healing and minimises the use of antibiotics. The side effects
| |
| − | of antibiotics include the development of bacterial resistance, anaphylactic reactions, overgrowth of bacteria and gastrointestinal disturbances.
| |
| − | | |
| − | '''Important note'''
| |
| − | '''Antibiotics seldom eliminate infection – rather they reduce the rate of bacterial replication to a degree that allows the hosts’ immune system to eliminate the infectious agent.'''
| |
| − | | |
| − | <u>The donkey is particularly sensitive to tetanus toxins</u> and the untreated
| |
| − | disease carries a hopeless prognosis. Therefore, the '''tetanus vaccination status''' should be established in all cases. If the donkey has had a recent vaccination then there should be no risk of the disease (the vaccine is highly effective) but, where vaccination history is dubious, either a tetanus toxoid booster vaccination or antiserum (or both) should be administered.
| |
| − | | |
| − | ===6. Wound debridement===
| |
| − | [[Image:Wound debridement.jpg|right|thumb|250px|<small><center>Debridement under general anaesthesia to remove the infected and unhealthy tissue. (Image courtesy of [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary])</center></small>]]
| |
| − | [[Image:Wound healing.jpg|right|thumb|250px|<small><center>Wound healing takes place rapidly once all the obstacles have been
| |
| − | removed. Note the very healthy pink colour and the epithelial margin. (Image courtesy of [http://drupal.thedonkeysanctuary.org.uk The Donkey Sanctuary])</center></small>]]
| |
| − | Ideally, all foreign matter and necrotic or non-viable tissue should be
| |
| − | removed, using a scalpel and dissecting forceps, to convert an accidental wound into a surgical one that can be closed by first intention. Although this ideal is seldom achieved it is an important target. '''Debridement of
| |
| − | contaminated or devitalized tissue should be accomplished systematically''',
| |
| − | starting at the most dependent part of the wound so that bleeding does not
| |
| − | conceal tissue that should be removed. Repeated partial debridement can be
| |
| − | performed to produce a clean, healthy wound site. Surgical debridement may
| |
| − | be delayed until it is possible to differentiate between viable and devitalised
| |
| − | tissue. Extensive debridement may require general anaesthesia – this
| |
| − | has major advantages in terms of accuracy and detail but circumstances
| |
| − | will vary.
| |
| − | | |
| − | '''Important note'''
| |
| − | '''In anatomical sites that have little ‘spare’ skin (e.g. the distal limb regions and the face) or where skin deficits are likely to have serious limiting effects (e.g. the eyelid), skin should be preserved as far as possible.'''
| |
| − | | |
| − | '''As a general rule, skin should be preserved unless its presence is likely to do more harm than good. Even non-viable skin can act as a useful (if temporary) biological cover for wound site.'''
| |
| − | | |
| − | Antibiotics can never replace good wound management principles. The
| |
| − | inability to create a completely sterile wound by debridement and lavage
| |
| − | can be partially (but NOT totally) compensated for by antibiotics applied
| |
| − | locally and administered systemically. Provision of adequate drainage
| |
| − | (through placement of drains), partial suturing and counter incisions to
| |
| − | reduce fluid and tension at the wound site can also help to limit the chances
| |
| − | of infection.
| |
| − | | |
| − | ===7. Wound closure===
| |
| − | | |
| − | The choice of wound closure method is governed by the nature and site
| |
| − | of the wound and is a matter of clinical preference. Wounds subjected to
| |
| − | [[Healing Fundamentals - Donkey#Primary or first intention healing|primary wound closure]] or first intention healing will usually heal faster
| |
| − | than those subjected to either [[Donkey - Fundamentals of healing#Delayed primary healing|delayed primary healing]] or [[Healing Fundamentals - Donkey#Secondary or second intention healing|second intention healing]].
| |
| − | | |
| − | Incised wounds frequently lend themselves to suturing. Suturing should
| |
| − | only be carried out when so doing will have a positive advantage and minimal
| |
| − | harmful effects. Careful selection of suture patterns will make a considerable
| |
| − | difference to wound healing. No wound should be completely closed unless the deeper tissues are effectively sterile.
| |
| − | | |
| − | <u>Factors that are likely to result in wound breakdown (dehiscence) after suturing include:</u>
| |
| − | # Gross contamination, including hair matting over the wound.
| |
| − | # Infection.
| |
| − | # Significant skin loss (either occurring at the time of injury or arising afterwards from skin necrosis).
| |
| − | # Marked swelling with fluid and inflammatory exudate.
| |
| − | | |
| − | Proper preparation and careful assessment should limit these factors significantly.
| |
| − | | |
| − | '''Important note'''
| |
| − | * '''Delays in closure may result in contraction of the skin flaps and so preclude closure
| |
| − | * '''[[Healing Fundamentals - Donkey#Primary or first intention healing|Primary closure]] will almost always fail when tissue necrosis and swelling disrupt the suture line
| |
| − | * '''Notwithstanding the presence of obvious complication factors, wounds involving the lower parts of the limbs usually present the greatest challenges. There is considerable controversy over the need/necessity to suture lower limb wounds. In general, a limb wound may be sutured if the wound is:
| |
| − | | |
| − | # '''Clean.
| |
| − | # '''Free of complicating factors.
| |
| − | # '''In the longitudinal plane (i.e. running up/down the limb).
| |
| − | # '''In a suitable site that makes suturing without undue tension feasible.
| |
| − | * '''Otherwise it is probably best to use [[Healing Fundamentals - Donkey#Secondary or second intention healing|second intention
| |
| − | healing]] or [[Healing Fundamentals - Donkey#Delayed primary healing|delayed primary intention healing]]
| |
| − | | |
| − | [[Healing Fundamentals - Donkey#Delayed primary healing|Delayed primary closure]] may be applicable in relatively clean but
| |
| − | contaminated wounds with extensive tissue damage. The wound is '''cleaned,
| |
| − | debrided and dressed with a hydrogel and a polymeric foam dressing'''
| |
| − | applied. '''Daily re-examination''' and redressing continues until the wound is
| |
| − | free of obvious infection and necrotic tissue, and the wound bed contains
| |
| − | '''healthy granulation tissue'''. The wound is then freshened using careful,
| |
| − | '''superficial, sharp debridement and closed using a suitable suture technique'''
| |
| − | (possibly with the aid of tension-relieving quills or tension-relieving lateral
| |
| − | incisions).
| |
| − | | |
| − | [[Healing Fundamentals - Donkey#Secondary or second intention healing|Second intention healing]] is applicable to the large majority of wounds in donkeys. The '''wound is left open''' after initial treatment and '''allowed to
| |
| − | granulate'''. Once healthy granulation tissue fills the wound from its depth
| |
| − | and has reached the wound margin, the epithelium should be able to migrate
| |
| − | across the wound.
| |
| − | | |
| − | '''Wound contraction''' is a significant aspect of second intention healing.
| |
| − | On the body and neck over 95% of second intention healing is by
| |
| − | contraction and it occurs at a rapid rate. Contraction is weak in the distal
| |
| − | limb regions of donkeys in particular. Second intention healing is faster on
| |
| − | the body trunk than on the limbs where, at least in a proportion of larger
| |
| − | horses, the inflammatory process is weak and prolonged and so the wound
| |
| − | never heals (Wilmink et al, 1999).
| |
| − | | |
| − | ===8. Provision of an ideal (moist) wound healing environment===
| |
| − | | |
| − | A moist wound healing environment has become standard practice. Wounds heal better when maintained in this fashion (Winter, 1962). Alginate or highly absorptive dressings may be required if exudate is excessive, but should not be used in other circumstances.
| |
| | | | |
| | ==References== | | ==References== |
| | | | |
| | * Knottenbelt, D. (2008) The principles and practice of wound mamagement In Svendsen, E.D., Duncan, J. and Hadrill, D. (2008) ''The Professional Handbook of the Donkey'', 4th edition, Whittet Books, Chapter 9 | | * Knottenbelt, D. (2008) The principles and practice of wound mamagement In Svendsen, E.D., Duncan, J. and Hadrill, D. (2008) ''The Professional Handbook of the Donkey'', 4th edition, Whittet Books, Chapter 9 |
| − | * Wilmink, J.M., Stolk, P.W.T., van Weeren, P.R., and Barneveld, A. (1999). ‘Differences in second intention wound healing between horses and ponies; macroscopical aspects’. ''Equine Veterinary Journal 31''. pp 53-60.
| |
| − | * Winter, G.D. (1962). ‘Formation of the scab and the rate of epithelialisation of superficial wounds in the skin of the young domestic pig’. ''Nature 193''. pp 293-294.
| |
| | | | |
| | | | |