I. INTRODUCTION
HB trimming is still used worldwide for retrimming birds on farm where required to reduce the risk of or control serious outbreaks of cannibalism and feather pecking. In the review by Glatz (2000) other methods of trimming included a gas beak trimming machine, an electric soldering iron and a cold blade. These methods are only practical to use when retrimming birds on smallholder farms as they are too slow to use on a large number of birds on a commercial farm. This paper aims to reaffirm the research which identified best practice HB trimming that was included in previous Australian Model Codes of Practice for the Welfare of Animals – Domestic Poultry (Welfare Code) in 1992, 1995 and 2002. HB trimming has been banned in many European countries and IRBT in some because of the concerns from animal rights organisations and consumers. It was clear from the early research, that IRBT was a superior method of tipping (Glatz, 2005) and this was acknowledged in later research by McKeegan & Philbe (2012). Since then, there has been little attempt to repeat the work which led to development of best practice HB beak trimming as defined in the 1992, 1995 and 2002 Welfare Codes. Instead, most of the beak tipping research has been about understanding the effects of IRBT on beak physiology and growth and defining best practice IRBT. This research (Dennis, 2009 & 2012; Carruthers, 2012) included comparisons made with the standard HB method used in the country where the research was conducted. Gabrush (2011) did compare the severity of HB beak trimming for day old chicks using the guide-plate on the trimming machine which has 3-hole sizes (4, 5 and 6 mm in diameter). HB treatment was successful in effecting the degree of beak shortening with beak length being 14, 31 and 39% shorter than the control treatment at 11 weeks of age. Histological examination of the beaks did not find neuromas, supporting the best practice method for HB trimming reported in the 1992, 1995 and 2002 Welfare Codes.
II. HOT BLADE TRIMMING
Research by Glatz (1987, 1990) had identified that HB trimming birds at hatch and removing half of the upper beak and one third of the lower resulted in less stress to birds and better performance than beak trimming birds at older ages. Glatz (1990) showed that chickens trimmed at hatch have better feed conversion than those trimmed at 10 or 42 days of age. Hester and Shea-Moore, (2003) also reported that better egg production is obtained when birds are HB trimmed earlier.
The initial pain reactions to HB trimming can be divided into 3 phases; painless, acute, and chronic. Acute pain (2h to a few days) results from stimulation of nociceptors (pain receptors) in the tip of the beak and follows a pain free period (up to 26h) normally associated with action by the birds’ endogenous analgesia system (Cheng, 2005). Neuromas form in the beak when axons are severed because of beak trimming (Lunam, 2005). They may develop as scattered micro neuromas which regress (one-half upper beak, one third lower beak trim) or in the case of severe beak trimming (two-thirds of upper beak; one-half of lower beak) neuromas may persist and discharge action potentials that may be perceived by the bird as chronic pain.
III. INCIDENCE OF NEUROMAS
Lunam et al. (1996) used the recommendation from Glatz (1987, 1990) to beak trim birds at hatch with a hot blade. The incidence of neuromas at 10 and 70 weeks-of-age in untrimmed birds was compared with chicks given a moderate trim (i.e. one half the upper beak removed (3 mm) and one-third of the lower beak removed (2.5 mm) versus birds with a severe trim where two-thirds of the upper beak (4 mm) and half of the lower beak (3mm) was removed. The results were consistent with other work (Keunzel, 2007) and indicate that neuromas do form after trimming but resolved in birds moderately trimmed, with sensory corpuscles still present in the upper and lower beak. Neuromas (consisting of masses of disorganised tangles of nerve fibres) only persisted in birds that had been severely trimmed and may discharge ectopic spontaneous action potentials perceived as pain.
The moderately trimmed birds had a 25% reduction in beak length compared to control birds at 70 weeks while the severely trimmed birds had a reduction of 50-65% in beak length as compared with control birds. Beak trimming younger birds (less than one week of age) appears to avoid the long-term chronic pain that can occur in the stump of the beak when older birds are trimmed (Lunam et al, 1996) and suggests that beak-trimming at an early age decreases the formation of scar tissue and reduces the risk of neuroma development. A likely explanation for this is that the beak of young birds has a greater capacity for regeneration compared to the regenerative ability of older birds.
A case was then made by Gentle (1998) who had previously recommended a ban on HB trimming to continue HB beak trimming in young birds using moderate trimming (Gentle, 1988) as previously recommended by Glatz (1987,1990) and Lunam et al. (1996).
Work by Glatz (1987, 1990) was included in the 1992 Welfare Code recommending that HB trimming of half of the upper beak and one third of the lower beak be practiced on chicks early in life. Gentle et al (1997) suggested that anything less than 50% top beak removal results in extensive re-growth and this can lead to outbreaks of feather pecking and cannibalism after beak trimming and hence the need to retrim birds if the one-third rule is adopted. To investigate impact of retrimming, an anatomical and behavioural study examined the effects of moderate hot blade beak-trimming of chickens (as specified above) on the day of hatch and retrimming of 2 mm of the upper and lower beak at 14 weeks-of-age (Lunam, 2005). Beak trimming was conducted per industry standards for beak trim accreditation (Bourke et al., 2002a, b). A heated blade on a commercial electric beak trimming machine (Lyon Electric Company) cut and cauterised half the upper beak and one-third of the lower beak for 2s. At 14 weeks of age chickens were re-trimmed using a heated blade that removed 2 mm of the upper and lower beak. The wound was cauterised with the heated blade for 2s.
Sensory receptors and individual nerve fibres were observed near the tips of the retrimmed upper and lower beaks at 28 weeks-of-age. In the tip of the lower beak, large Herbst corpuscles were present and many nerve bundles traversed the dermis between the mandibular bone and epidermis of the beak tip. At 66 weeks-of-age, sensory receptors and nerve fibres were observed in the dermis at the beak tip (Lunam, 2005). The hens returned to normal feeding and pecking behaviours by 66 weeks-of-age (Jongman et al. 2008) and supported the microanatomy that the sensory input to the beak is restored after retrimming.
IV. BEAK TRIMMING CODE OF PRACTICE
The early findings on hot blade trimming by Glatz (1987, 1990) were recognised in the 1992 Australian Model Code of Practice for the Welfare of Animals. Domestic Poultry Edition 2 (and again in Edition 3, 1995) (see page 13 Management Practices (12.2.1 and 12.2.2) where one half of the upper beak and one third of the lower beak may be removed in day old to 10- day old birds) and were supported by the later findings of Lunam et al. (1996) and Gentle (1988).
In the 2002 Australian Model Code of Practice for the Welfare of Animals, Domestic Poultry, it specified that beak trimming of birds be conducted using an accredited trainer under an accredited training program in accordance with an agreed accreditation standard. The co-author of this paper was requested by RIRDC’s Egg Program to develop an accreditation standard and publish a training manual for HB trimmers and worked with TAFE (NSW), VIAS and PIRSA (see Bourke et al., 2002) to develop the standards.
V. CONCLUSION
IRBT is the most popular method to beak tip poultry in Australia. The HB method is used for re-trimming flocks during the rearing period if beaks have regrown after treatment at hatch with the infrared method. Where IRBT is not available at small hatcheries, HB trimming is used for the first trim and a second trim where required. The standard developed for hot blade beak trimmers was referred to in the 1992, 1995 and 2002 Australian Welfare Codes and involved removal of no more than half the beak length and to provide a step to the lower beak for birds trimmed at day old to 10-12 days-of age (see P. 68 of Bourke et al. 2002b). This standard is still used today.
Abstract presented at the 30th Annual Australian Poultry Science Symposium 2019. For information on the latest edition and future events, check out https://www.apss2021.com.au/. 
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