Calf disbudding – animal welfare considerations

ABSTRACT

Disbudding, removal of the horn buds, is performed for economic and practical reasons: to prevent bullying and injury to other animals (with implications for productivity and carcass damage, respectively) and human safety during handling. Mitigation of pain associated with the disbudding of calves is necessary to limit the pain-stress response that induces altered behavioural and physiologic states. The most common recommendation in Animal Welfare Guidelines is to disbud calves before they attain 2 months of age. From birth to 2 months of age the horn bud is not attached to the skull, which makes the removal of the horn bud and adjacent cells easier. The objectives of this review are to describe (1) the different methods of disbudding, (2) the pain responses associated with each of those methods and (3) how age and pain mitigation strategies affect those responses.

KEYWORDS:

• Disbudding
• methods
• age
• horn bud size
• pain relief

1. Introduction

Disbudding involves the removal of immature horn tissue (horn ‘buds’ growing from the skin), from which the horns of the animal subsequently develop (Mellor and Stafford 2004; Bates et al. 2016; Adcock et al. 2019, 2020; Duffield and Winder 2022; Reedman et al. 2022; Schoiswohl et al. 2022). After approximately 2 months of age, the horn buds attach to the skull. The removal of the horns after this age is called dehorning (AVMA 2014). There is evidence that disbudding is less painful than amputation dehorning (Petrie et al. 1996; Huxley and Whay 2006; Stilwell et al. 2007; Hokkanen et al. 2015; Moggy et al. 2017). For this reason, disbudding is preferred compared to dehorning from a welfare point of view. Research conducted by Dwane et al. (2013) using focus groups reported that some Irish beef farmers were reluctant to use local anaesthetic (LA) and opted to disbud calves less than 14 days old in order to avoid using it, even when the horn bud had not erupted. This may indicate a lack of knowledge concerning aspects of the disbudding procedure and the application of LA. Research indicates that young calves may be equally or possibly more sensitive to pain than older calves (FRAME 2001), supporting the farmers’ opinion that older calves are better able to withstand the pain of disbudding than younger calves and raising questions about the validity of age-related anaesthetic guidelines. These age limits, where specified, range from 3 weeks to 6 months. Legal provisions in other jurisdictions outside Ireland show a range of age limits set for disbudding (Table 1). There is also evidence to suggest that disbudding near birth does not improve welfare outcomes and there is some evidence to suggest it may produce a generalized long-term increase in pain sensitivity (Tucker 2018). In accordance with EFSA opinions (2006, 2012), many countries surveyed now require the use of LA for disbudding, irrespective of age. The 2009 ALCASDE report recommended that disbudding must be done by trained personnel and that specific techniques must involve pain alleviation using anaesthetic and non-steroidal anti-inflammatory drugs. However, almost as many other countries allow disbudding without LA for some of or the entire allowable age limit.

Table 1. Legislation concerning the use of anaesthesia for disbudding calves.

Country	Methods allowed	Anaesthesia required	Reference
Ireland	Hot-iron	All methods: over 15 days of age	S.I. No. 107 (2014)
United Kingdom	Hot-iron caustic paste^a	Hot-iron: at any age caustic paste: none	DEFRA (2013)
Germany	Not specified	All methods: over 6 weeks of age	Daanje (2013)
Belgium	Not specified	At any age	Daanje (2013)
Australia	Hot-iron caustic paste	All methods: over 6 months of age	Animal Health Australia (2016)
New Zealand	Not specified	At any age	Reddy (2018)
Canada	Not specified	Dairy: at any age beef: Not specified	National Farm Animal Care Council (2013)

^a Allowed but strongly not recommended.

The scientific community and producers worldwide (Huxley and Whay 2006; Hokkanen et al. 2015; Moggy et al. 2017; Reedman et al. 2022; Roder et al. 2022; Schoiswohl et al. 2022) agree that disbudding is a painful procedure, regardless of the age of the calf and recommends the use of a local anaesthetic in combination with an analgesic as a measure to alleviate pain during this procedure (reviewed by Herskin and Nielsen 2018; Winder, Bauman et al. 2018; Reedman et al. 2022; Roder et al. 2022; Schoiswohl et al. 2022). Martin et al. (2022) recently reported that the administration of bupivacaine liposome suspension as a cornual nerve block at the time of dehorning was as effective at controlling pain as a multimodal approach of lidocaine and meloxicam.

Legislation concerning the use of pain relief during and post-disbudding varies among countries. While the use of anaesthetics is mandatory during the disbudding of calves at any age in New Zealand, Belgium and the United Kingdom, calves can be disbudded without the use of anaesthetic up to a certain, specified age in Australia, Germany and Ireland (Table 1). Cozzi et al. (2015) reported in their survey that pain relief protocols have shown to be inconsistent within and between EU Member States. The authors suggested that an introduction of transnational legal standards concerning disbudding and dehorning should help to a harmonization of the current inconsistent drug protocols observed within and between countries (Cozzi et al. 2015). According to a large European survey carried out in 2008 (ALCASDE 2009), 40% of beef farms (which corresponded to approximately 40% of beef cattle) kept bulls without horns. Of this population, 63% were disbudded (52% of these by hot iron and 48% by caustic paste) and 35% were dehorned. About 2% of the beef cattle population were from polled breeds. The legislation concerning the use of anaesthesia for disbudding in cattle varies considerably among different countries within the EU and internationally, depending on the method involved and age of the animal (Table 1).

2. Reasons for disbudding of calves

Removal of the horns in cattle is carried out to reduce the risk of injuries to humans, and of other animals in the herd (Menke et al. 1999; Knierim et al. 2015). It also reduces the incidence of carcass wastage due to bruising (Meischke et al. 1974). Hornless animals also require less space at the feed bunk in confined systems. Cattle with horns are more difficult to handle in yards and chutes; require three times more space at a feed trough and during transport (McMeekan et al. 1999); exhibit fewer aggressive behaviours associated with individual dominance (Bouissiou 1972); and may suffer financial penalties on sale. In general, there is no obligation to dehorn cattle in Europe. However, in some Member States (including UK, Ireland and Austria) animals that are presented for sale at auction markets must be dehorned (ALCASDE 2009). According to the Transport Regulation (2005) it is illegal to mix horned and non-horned animals during transport unless they have been raised in compatible groups and dehorned cattle are often a requirement of the slaughter industry. In Ireland, it is prohibited to sell or export horned animals under Statutory Instrument ((S.I.) No. 224 of 2014 (Animal Health and Welfare (Restriction on Horned Cattle) (No. 2) Regulations 2014)) other than under certain very limited conditions (Animal Health and Welfare Act 2013).

3. Disbudding methods

The horn bud-producing cells (corium) and the surrounding tissue need to be destroyed or removed to prevent horn re-growth (Vickers et al. 2005). Since the horn bud is not attached to the skull until after 2 months of age, horn buds can be removed easily without opening the frontal sinus. Therefore, disbudding is preferred compared with dehorning of older animals. The most common methods of disbudding are cautery (thermal or chemical) or physical. Thermal (hot-iron) or chemical (caustic paste) cauterization destroys the horn-producing cells, while physical method removes them (Vickers et al. 2005). The choice of method depends on the current legislation and farmers’ experience and preference.

3.1. Hot-iron disbudding (thermal cauterization)

Cautery or hot-iron disbudding is recommended by the European Food Safety Authority (EFSA) and other authority organizations, and is the only method of disbudding allowed in Ireland under Statutory Instrument (S.I.) No. 127/2014 – Animal Health and Welfare (Operations and Procedures) (No. 2) Regulations 2014, which permit disbudding of calves up to 28 days old by this method. Hot-iron disbudding is the most common disbudding method, reported to be used in 71% of the farms in Europe (Cozzi et al. 2015). Using this procedure, the concave tip of the disbudding iron, heated to over 600°C, is applied to the base of the horn bud for approximately 10 s, causing the destruction of the horn bud and generative tissues (Weaver et al. 2005). The heat cauterizes the blood vessels around the wound; no bleeding should occur if the procedure is properly done. Hot-iron disbudding causes third-degree burns where the hot iron is applied and first and second-degree burns on surrounding tissues (Taschke and Folsch 1997). It is suggested that excessive heat applied during hot-iron disbudding could damage the underlying bone (Kihurani et al. 1989). Besides that, disbudding via cauterization may be less stressful compared with scoop disbudding because nociceptors are destroyed by heat and pain perception is consequently reduced (Petrie et al. 1996). Electrical and butane hot-iron disbudding devices are available for this procedure.

3.2 Caustic paste (Chemical cauterization)

A caustic paste containing sodium hydroxide and calcium hydroxide is applied to the horn bud to damage the horn-producing cells. The damage continues as long as the active chemicals are in contact with tissue (Vickers et al. 2005). Dehorning with caustic paste induces pain, but the pain is reported to be less than that caused by the hot iron, even when using lidocaine (Vickers et al. 2005). Despite the lack of robust scientific evidence, caustic paste disbudding has been suggested to be one of the least painful methods for horn bud removal (Vasseur et al. 2010). However, the potential longer-term welfare consequences of this method (i.e. inflammatory pain, healing time, horn regrowth, injuries from chemical run-off) are unknown and, to date, few studies have found a way to mitigate the acute pain response associated with caustic paste (Stilwell et al. 2009; Vasseur et al. 2014; Winder, Bauman et al. 2018). Caustic paste was reported to be used in only 26% of farms in Europe (Cozzi et al. 2015) while a study by Ede et al. (2020) suggest that calves initially remember caustic paste disbudding as a more negative experience than hot-iron disbudding, even with the use of sedation, local anaesthesia and analgesia. While there is very limited research examining pain mitigation of calves disbudded with caustic paste compared to similar work in cautery, the current evidence supports the use of local anaesthesia combined with NSAID analgesia as effective for reducing pain when disbudding using caustic paste (Reedman et al. 2020).

3.3 Clove oil or isoeugenol

Clove essential oil (Caryophylli aetheroleum) has anaesthetic, analgesic, antibacterial and cytotoxic properties mainly associated with its principal active component eugenol (Chaieb et al. 2007). Similar properties have also been shown for the eugenol-isomer isoeugenol. The cytotoxicity of eugenol was reported to be 1 order of magnitude lower than that of isoeugenol in-vitro (CC50: eugenol, 0.395 mM; isoeugenol, 0.0523 mM); and reactive oxygen species (ROS) production was induced significantly by isoeugenol, but not by eugenol (Atsumi et al. 2005). Due to the combination of cytotoxic and anaesthetic effects, clove oil and isoeugenol have been investigated as an alternative to hot-iron disbudding in goats and calves (Sutherland et al. 2013, 2002; Molaei et al. 2014, 2015; Frahm et al. 2020; Juffinger et al. 2021). Still Brooks et al. (2021) reported that clove oil injection was associated with several unexpected and severe complications in kid goats including unintended tissue necrosis, temporary paresis, skull defects, meningitis and death. The general consensus in the literature is that neither the injection of clove oil or isoeugenol was as effective as the use of a hot iron in preventing horn growth and the injection of clove oil was not recommended. In agreement, a recent study by Schoiswohl et al. (2022) reported that while alternative treatments (especially isoeugenol) may cause less severe tissue damage than hot-iron disbudding, the authors recommended that further research is necessary to optimize the injection volume and technique. To our knowledge, no study has investigated the welfare implications or long-term consequences of isoeugenol as an alternative to hot-iron disbudding.

3.4. Scoop dehorning (Physical removal)

This method involves the physical removal of the horn buds using knives, a scoop or tubes. It is important that the corium and a complete ring of hair surrounding the horn bud should also be removed to prevent horn regrowth (AVMA 2014). The method is reported to be used by 3% of European farmers (Cozzi et al. 2015).

4. When to disbud calves

Animal Welfare Guidelines recommend the disbudding of calves before they attain 2 months of age (EFSA 2012). As previously mentioned, from birth to 2 months of age the horn bud is not attached to the skull, which makes the removal of the horn bud and adjacent cells easier. The Code of Recommendations for the Welfare of Livestock from the United Kingdom recommend that disbudding should take place before calves are 2 months old and ideally as soon as the horn bud becomes visible (FAWC 2012; DEFRA 2013). Other organizations for animal welfare from Ireland, Australia, recommend disbudding calves as young as possible, without specifying the optimum age (FAWAC 2003, 2008; Animal Health Australia 2016). Even though there is a general recommendation to disbud calves before they attain 2 months of age, there is no agreement on when calves should be disbudded within the 2 month period. In addition, regulatory organizations permit painful procedures without pharmacological anaesthesia or analgesia in animals under a certain age, even though there is much evidence that the use of pain relief is efficient and should be used when disbudding calves (reviewed by Coetzee et al. 2012; Guatteo et al. 2012; Coetzee 2013; Stock et al. 2013; Stock and Coetzee 2015; Herskin and Nielsen 2018; Winder, Miltenburg et al. 2018).

5. Impact of disbudding on calf welfare

Tissue damage caused by disbudding results in the activation and release of intracellular contents from damaged cells, inflammatory cells and nerve fibres (Anderson and Muir 2005). In addition, physiologic, neuroendocrine and behavioural changes indicatives of pain and distress are observed following disbudding (McMeekan et al. 1998; Vickers et al. 2005). Increased levels of circulating corticosteroids, such as cortisol, reflecting changes in the hypothalamus-pituitary-adrenal axis are commonly detected after disbudding. Plasma cortisol concentrations increase 30–60 min after disbudding and return to baseline values approximately 6–8 h after the procedure (Wohlt et al. 1994; McMeekan et al. 1997; McMeekan et al. 1998; Mellor et al. 2000; Stewart et al. 2008; Stewart et al. 2009). Wohlt et al. (1994) reported plasma cortisol concentrations of 21.9 ng/ml for 3-week-old Holstein calves that were dehorned using an electrically-heated instrument, in comparison to 11.3 ng/ml for control animals. Similarly, a study of electrical dehorning of 8-week-old calves, by Laden et al. (1985), found increased plasma cortisol concentrations compared to controls, although there were no effect of dehorning on blood packed cell volume or plasma glucose. Morisse et al. (1995) compared electrical and caustic methods of dehorning of 4- to 8-week-old calves, each with and without local anaesthesia. Both methods of dehorning increased plasma cortisol and produced changes in behaviour for about 4 hours, including restlessness, head-shaking and decreases in social behaviour. There were no differences in plasma cortisol between electrical and caustic dehorning methods, but calves dehorned using the electrically heated instrument tended to exhibit less intense behavioural reactions. The provision of local anaesthesia reduced cortisol in calves dehorned using caustic paste, and the intensity of the behavioural responses in both the caustic and electrical dehorned treatments. Taschke and Folsch (1993) identified particular behavioural patterns that were exhibited to a much greater extent by electrically dehorned calves in comparison with sham-dehorned calves. These behavioural patterns included rearing, tail-wagging and attempted escape during treatment, and subsequent head scratching, head shaking, standing with the head lowered and suppression of normal behavioural activity, which Taschke and Folsch (1993) classed as ‘depression’.

Postoperative behavioural indicators of pain, such as head rubbing, head shaking, ear flicking, tail flicking, increased numbers of transitions between lying and rising and reduced rumination were also reported following disbudding (Faulkner and Weary 2000; Sutherland et al. 2002, 2013; Stilwell et al. 2007). There is also evidence that hot-iron disbudding reduces play behaviour (Mintline et al. 2013), and produces a negative change in emotional state of dairy calves (Neave et al. 2013).

Disbudding performed without pain mitigation is viewed as a key welfare issue. Administration of local anaesthetics is reported to reduce the initial increase in plasma cortisol concentration and behaviours associated with the immediate and postoperative pain response (Morisse et al. 1995; Sylvester et al. 1998, 2004; Graf and Senn 1999; McMeekan et al. 1999). The use of a non-steroidal anti-inflammatory drug (NSAID) in addition to local anaesthesia has generally been found to be advantageous (Faulkner and Weary 2000; Milligan et al. 2004; Stilwell et al. 2009; Heinrich et al. 2010; Allen et al. 2013; Stock et al. 2016). Reductions in plasma cortisol, pain behaviours and pressure sensitivity were reported when NSAID was administered in combination with a local anaesthetic at 3, 4 and 6 h post-disbudding (reviewed by Stock et al. 2013; Winder, Bauman et al. 2018). Therefore, the use of local anaesthetic combined with an NSAID is recommended best practice for pain mitigation for cautery disbudding. However, as highlighted by Winder, Miltenburg et al. (2018), studies addressing the magnitude or duration of NSAID treatment are very heterogeneous. Therefore, it is still difficult to draw specific recommendations concerning the use of analgesia during and post disbudding.

The genetic selection for polled cattle may be a long-term solution to reduce the need for disbudding (Spurlock et al. 2014). Although polled genetics have been introduced for beef breeds, only 4.9% of European farms have polled cattle (Cozzi et al. 2015). Therefore, disbudding and dehorning are still performed both in beef and dairy farms in Europe; 81% of the dairy, 47% of the beef and 68% of the suckler cows are dehorned (Cozzi et al. 2015).

6. Disbudding practices and use of pain relief

A European study reported that 81% of the dairy, 47% of the beef and 68% of the suckler production systems have disbudded/dehorned animals, and a low prevalence of polled animals especially in the dairy cattle sector (Cozzi et al. 2015). The study also found that only 57.2%, 37.9% and 35.3% of the dairy, beef and suckler systems, respectively reported to use some form of medication prior to disbudding (Cozzi et al. 2015). The authors did not provide the breakdown of medication according to the use of sedation, local anaesthesia, analgesia or a combination of the main treatments. The administration of an NSAID alone is reported to lower cortisol concentrations earlier than if no pain control is provided but did not eliminate the cortisol peak reported in the first 30 min after disbudding (Glynn et al. 2013; Stock and Coetzee 2015; Reedman et al. 2020; Reedman et al. 2022). It was also reported that when both local anaesthetic and NSAID were administered to calves prior to disbudding, the acute and delayed cortisol responses were eliminated (Stilwell et al. 2009; Winder, Bauman et al. 2018; Reedman et al. 2020, 2022). While the local anaesthetic is effective at reducing acute pain (the first cortisol peak) for 1–3 h after disbudding, the NSAID works to prevent the secondary peak, which usually occurs 4 h after disbudding, through anti-inflammatory properties. However, Winder, Miltenburg et al. (2018) in their meta-analysis found that in some cases, the cortisol response of calves provided with both medications did not differ from the responses of sham-disbudded control calves. The use of local anaesthesia and sedation is partly associated with the operator, as in some countries use of anaesthetics or sedatives are legally restricted to veterinary practitioners. Also, the availability of drugs for farmer use is regulated differently in various countries, so that farmers may or may not have access to local anaesthetics, NSAIDS or sedatives. Stafford and Mellor (2011) highlighted that the administration of a cornual block and an analgesic are simple procedures of which, in communities of smaller farmers, a local veterinary technician can easily be trained to do it. Therefore, in countries where the provision of pain relief is mandatory for such procedures, legislators and regulators have made other regulatory adjustments to allow non-veterinarians to administer such drugs and carry out such procedures (Stafford and Mellor 2011; Spoolder et al. 2016). In 2015, the stockman was reported to be the main person in charge of calf disbudding in Europe (72% of hot iron disbudding, 92% of caustic paste and 60% of scoop disbudding) (Cozzi et al. 2015).

The legislation in Ireland permits disbudding of a bovine that has not attained the age of 28 days by farmers, without a presence of a veterinary practitioner (S.I. No. 127 of 2014). In any case, Irish farmers must use anaesthesia or analgesia (with a veterinary prescription) when disbudding calves between 15 and 28 days of age. Disbudding of calves older than 28 days must be performed by a veterinary practitioner and the use of local anaesthesia and analgesia is mandatory for the procedure (Statutory Instruments (S.I.) No. 127 and 107 of Animal health and welfare regulations, 2014). Adrenacaine (procaine with adrenaline) is the only authorized local anaesthetic for use in calves, by farmers with prescription, for disbudding in Ireland (Health Products Regulatory Authority (HPRA) 2015). The presence of adrenaline in the composition of adrenacaine may prolong the duration of action of the drug (French and Sharp 2012). However, evidence supporting the efficacy of adrenacaine as a local anaesthetic during the disbudding of calves is limited. A study by Thomsen et al. (2021) reported that 42% of calves, having received local anaesthetic and disbudded with a hot iron, showed at least 1 of 3 behaviours (getting up, kicking, or lifting head), which the authors suggest may have been due to the type of LA administered, the time interval from LA administration to disbudding (range: 2–35 min) and the tip diameter (23 or 33 mm) of the hot-iron disbudder.

7. Age at disbudding and horn bud size

Most of the recommendations and legislations concerning when the disbudding should be performed are based on the age of the calves. There is variation in the suggested upper age limits for disbudding of calves ranging from 2 to 8 weeks of age. These age limits are not based on empirical evidence, but rather on opinion related to the physical development of horns in calves and that the horn buds become attached to the underlying periosteum at approximately 2 months of age. Particularly, the Code of Recommendations for the Welfare of Livestock from the United Kingdom recommends that disbudding should take place ideally as soon as you can start to see the horn bud (DEFRA 2013). In general, the size (diameter and height) of the horn bud is a visual aspect which farmers use to guide when to perform disbudding.

There is limited information in the literature on age at cautery disbudding for suckler-bred beef calves with most studies reporting on cautery disbudding of dairy-bred calves. More recently, Marquette et al. (2021) reported that the mean (SD) age of Holstein–Friesian male calves at disbudding was 37 (10) days while the corresponding ages for female and male suckler beef calves were 26 (8) (Charolais), 28 (9) (Limousin), 23 (6) (Simmental) days and 24 (7) (Charolais), 26 (7) (Limousin) and 23 (6) (Simmental) days, respectively. Stanek et al. (2018) reported a median age of 20 days (2.9 weeks) for dairy calves on Czech farms; Vasseur et al. (2010) reported a median age of 6.4 weeks in Canada; Gottardo et al. (2011) reported a mean of 4.6 weeks in Italy. The age range for disbudding reported by Stanek et al. (2018) on surveyed Czech farms ranged from 3 to 68 days of age. A possible reason why calves were disbudded before 28 days of age on Czech farms is that legislation allows the disbudding of calves without the use of pain relief for up to 28 days. There is variation across studies in the percentage of calves reported to be disbudded before 28 days of age. For example, Stanek et al. (2018) reported that 63.3% of Czech calves were disbudded which is greater than those reported in other studies: 21% in Canada (Misch et al. 2007), 25.7% in the US (Fulwider et al. 2008), 17% in southern Brazil (Hotzel et al. 2014) and lower than those reported (95%) in Finland (Hokkanen et al. 2015).

A number of studies have focused on the acute pain response to cautery disbudding (AVMA 2014, 2018; Winder et al. 2016; Winder, Bauman et al. 2018; Adcock and Tucker 2018, 2020, 2021; Herskin and Nielsen 2018) and of the benefits of providing local anaesthesia and systemic analgesia (Allen et al. 2013; Stock et al. 2013, 2016; Bates et al. 2015, 2016) at the time of disbudding. Adcock and Tucker (2018) reported that calves disbudded at 3 days versus 35 days of age were more sensitive to pain after disbudding. Similar findings of increased sensitivity are reported by Casoni et al. (2019) for up to 14 weeks post-disbudding of 7 and 28 days old Holstein calves. However, while local anaesthesia in addition to NSAID analgesia are of benefit in mitigating the pain-related disbudding behaviours, few studies have investigated the responses of contrasting breeds, sex and age of calves on recommendations of age-related anaesthetic and analgesic protocols. Caray et al. (2015) reported some effects of age, breed or sex on the behaviour of calves that were observed between 2 and 7 h after disbudding (for example 4-week calves and Charolais calves were more active than their 1-week-old Holstein counterparts), but found no interactions between age, breed, sex and treatment medication.

Marquette et al. (2021) in their investigation on the effect of age, breed and sex on horn bud size of dairy-bred and suckler-bred calves at the time of disbudding, reported that horn bud diameter and height were very variable across breeds which suggest that most of the variation is not explained by age. The research findings also indicated that the association between age and horn bud size was very weak in dairy-bred and suckler-bred calves. The horn bud size (diameter and height) was greater in dairy-bred calves than suckler-bred beef calves at the time of disbudding, and male suckler-bred calves had greater horn bud size than female counterparts (Marquette et al. 2021). The authors suggested that the variation observed, at least for the suckler-bred calves, could be attributed to calf sex since male suckler-bred calves had a greater horn bud height (29.1%) and diameter (8.8%) compared with female suckler calves at time of disbudding (Marquette et al. 2021). However, this finding is not unexpected for male calves as there is general agreement that the main evolutionary benefit of males having larger horns than females relates to intra-sexual competition for mates (e.g. Preston et al. 2003; Bro-Jørgensen 2007; Knierim et al. 2015). The implications of the findings by Marquette et al. (2021) were that calves should be disbudded while horn development is still at the bud stage and when the bud is large enough to be easily palpable/visible, but not too large that disbudding could lead to tissue trauma.

8. Conclusion

The degree of tissue damage associated with disbudding is influenced by the stage of development of the horn bud, for example, in younger calves the burning of the vessels surrounding the horn bud is sufficient, whereas the whole bud needs to be removed (by levering it out from the side) when the horn is further developed. Despite the visibility of the horn bud being the characteristic normally adopted by farmers when selecting animals for disbudding, most recommendations are based on the age of the calf. A calf should be old enough to have a horn bud, but not so old that the horns are too large when they are disbudded as the procedure could result in severe tissue trauma. Furthermore, depending on the procedure, calves with greater horn bud diameter at the time of disbudding may have more tissue damage which could lead to prolonged healing time and prolonged stress. In addition, the size of horn bud at the time of disbudding and that of the diameter of the disbudder tip are important considerations that need to be addressed in view of healing time. There are also limited studies on the time interval from the administration of LA to the hot-iron disbudding procedure, therefore further research is necessary to assess the pain responses of calves undergoing disbudding and the efficacy of the anaesthesia. This information would be useful to guide more specific recommendations on calf disbudding.

Disclosure statement

No potential conflict of interest was reported by the author(s).