ヒツジにおける羊毛食い

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ヒツジにおける羊毛食い

誌名

誌名 Animal behaviour and management ISSN

ISSN 18802133 著者

著者黄, 宸佑

竹田, 謙一巻/号

巻/号 51巻2号

掲載ページ

掲載ページ p. 65-72 発行年月

発行年月 2015年6月

農林水産省農林水産技術会議事務局筑波産学連携支援センター

Tsukuba Business-Academia Cooperation Support Center, Agriculture, Forestry and Fisheries Research Council Secretariat

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‑ Review ‑

The w o o l ‑ b i t i n g behaviour o f sheep: a short review

Chen‑Yu Huang'*， Ken‑ichi Takeda2*

'Interdiscip1inary Graduate Scho01 of Science and Techn010gy， Shinshu Universi句ら Minamiminowa，Nagano 399・4598，Japan

21nsti加teofAgric叫ture，Academic Assemb1y， Shinshu Universi臥Minamiminowa，Nagano 399‑4598， Japan

* Corresponding author. E‑mai1 address:12st553a@shinshu‑u.acj.p. ktakeda@s凶 shu‑u.acj.p

A b s t r a c t

In housed sheep， wo01‑biting is a serious behavioural prob1em. It not only 1et received animals injuring in their skin， but也eperformers of也isbehaviour may die企omdigesting troub1es. Although the occurrence of wo01‑biting behavio^ぽ isa serious impact on^{姐血}alwe1fare， but the factors that induce出sbehaviour are still unclear. Although it is believed也atsome rearing managements such as raising space and feeding processes， or也edeficiency of certarn nuむients1ike sulfur or zinc， are the potential factors to 1ead sheep into wo01ゐitingbehaviour， some points of view are 1ack of evidences. Since the factors^{紅巴} notso clear， it is di伍c叫tto prevent the occ^国Tenceof出IS behaviour or to con甘01the situation when it was alr巴adyhappened. In this pap巴r，we reviewed recent researches and summarized也eth巴on巴sabout woo1‑biting behaviour of sheep to date.

Key Words: abnormal behaviour; woo1‑biting; sheep; review

Animal Behaviour and Management， 51 (2): 65‑72， 2015 (Received 25 November 2014; Accepted for publication 6 December 2014)

Oral Stereotvoic Behaviours of Farm Animals Behaviour has usually been recognized as an indicator of heal出 andwe1fare in captive animals. Thus， the occurrence of stereotypic behaviours may point to the ex.ist巴nce of certain of deficiencies in artificial environments such as fanns^姐 dzoos， which have implications for the we1fare of animals. Stereotypic behaviours were defi.ned as abnormally repetitive， unvarying， and functionless behaviours that are often perfコrmed by captive animals housed in arti恥ialenvironments (S仰， 2011). Webster (1994) divided stereoザpicbehaviours into "movement" and

"ora1" types，阻dBergeron et a .l(2006) listed three principa1 hypotheses on the occurrence of oral stereotypic behaviours. First， anima1s do not often get enough gut fill or do not receiv巴sufficientnutrition， resulting in deficiencies in specific dietary

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mponents (e.g.， salt， prot怠in，fiber， or minera1)， or have too 1itt1e energy get， thus res叫tingin stereotypic behaviours as

M山nalsa仕emptto fi.nd mor巴foodor he1p addr巴ssthese underlying deficiencies. Second， captive姐 imalstake too litt1e time to fi.nd and consume也eirdai1y food ration. As a result， they have unfu1filled motivations to perform their natura1 foraging activities百illd，oral stereotypic behaviours are not d立巴ctlycaus巴dby也e quality or qu姐1ityof tlleir diet， but by也巴立伊t function

Some ora1 stereotypic behaviours are believed to be associated wi白血e feeding process because these usually occぽ around prandial activities (e.g.， McGreevy組 dNico1， 1998; Cooper etα l.2005). As animals maintained in environmentally enriched surroundings， they are al10wed to search food合omthis environment. Thus， SUIVlvrng them with some environment enrichments about feeding or foraging re1ated behaviours may reduce certain of stereotypic behaviours (B1okhuis， 1986; Norgaard‑Nie1s巴netα .l 1993). Oral stereotypic behaviours have been reported in various species. Bergeron et α 1. (2006) has enum巴ratedthe oral stereotypic behaviours in cows， catt1e， sows， horses， and sheep. Although 也e occurrence of oral stereotypic behaviours usual1y indicates inappropriate feeding processes dwing rearing management， it sometimes also reflects i1lness or patho10gical conditions such as c01ic (Hillyer etα. 1 2002)， ulc巴ration(Nico1 et a .l2002)， and 10w gas住民

pH 1eve1s (Willard et a .l1977). Several oral stereo勿plC behaviours are se1f‑directed such as tongue‑rolling in cows (Sambraus， 1985) or targeted at 0也erobjects such as wood‑chewing in horses (Johnson et a. l1998). However， some are usual1y partrIer‑directed such as featller‑pecking in pou1try (B1okhuis and Wiepkema， 1998)， tai1‑biting in pigs (Schroder‑Petersen and Simonsen， 2001)， and woo1‑biting in sheep (Reinl1ardt， 2005). These activities may a1so res叫tin skin iniuries

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n王EWOOL‑BIT町GOFSHEEP and hemorrhage in出巴 victimsor even death du巴to

cannibalism (Van Putten， 1969)

The occ^{町民}nceof oral stereotypic behaviours does not on1y affect the welfare of animals， it also decreases its productivity (Borell and Hぼnik，1990; Bergeron et a l.2006). In sows， for example， oral stereotypic behaviours increase energy use and reduce weight gain (Bergeron^組 d Gonyou， 1997). The cannibalistic behaviour such as feather‑pecking is also a serious welfare^祖 d economic problem on po叫町 indus町r

when birds are

町ぽ

edor kill吋 (Cloutieret a 2.l 002) Although ungulates are the most prevalent sp巴ciesthat engage in stereotypic behaviours^姐 d agricultural animals have been血efocus of extensive scientific studies (Bergeron et a .l2006)， stereotypic behaviours in sheep have not been extensively^巴xarnined(Lynch et a .l1992). Oral stereotypic behaviours in sheep include object‑licking， bar‑bitillg， slat‑chewing， and wool‑biting (Bergeron et al. 2006). Especially， wool‑biting in sheep is a p紅白巴r・directedoral activity (Fig.l)， sirnila r.to the abnormal behaviour known as

"hai r.pulling" in other anima1s， and has never been .

recorded in anima1s living in也enatura1 environment (Reinhardt， 2005). Th巴refore，the occurrenc巴 of出lS

cannibalistic behaviour indicates sheep are expenencing a pa.rticu1ar deficiency in its紅tificial re^征mgenV^lIonment

W001ゐitinqin Sheep

Sheep and 1ambs in farms sometimes deve10p a behaviour known as woo1‑biting (some a.rticles a1so use the terms as woo1‑pulling， woo1‑eating， or woo1‑chewing， and sometime rep1ace "woo1" with

"fleece")， in which the sheep bites off the woo1 fr.om other individuals. and then chews and swallows出lS

(Fig. 2). This behaviour is often sta.rts with a few numbers in the flock; howeve ，r.once sta.rted， it appears to spread across the who1e flock (Vasseur， et a 2.l006) We do not know if this behavioぽ isre1ative to breeds， but some res^巴archers have reported that出eallied species of sheep， the muskox (Ovibos moschatus)， a1so

Figure 1 A sheep (the standing one) is biting‑off wool from another individual (the sitting one). The receiver shown a highly tolerance to receive this behaviour.

pe.rforms wool‑biting (Reinhardt and Flood， 1983; Reinhardt， 1984). Wool‑biting is often observed in a

紺essfu1environment， and thus releasing these animals to也epasture often reduces出sabnOlma1 behaviour (Lynch et al. 1992). However， reports have also indicated that woo1‑biting occurs in grazing sheep (Huang， 2001; Huang and Chen， 2001; Shen， 2011).

The behaviour of woo1‑biting ^I^S usually accompanied by othe r.phenomena such as wool damage， alopecia， poor weight gain， 10st appetite， pica， and emaciation (lcen et a .l 2008). Para‑ or hyperkeratosis has a1so sometimes been reported (Akgu1 et al. 2001). Because sheep can not digest woo1，也epresence of ingested wool in th巴stomach，usually the abomasum， 1eads to the formation of hair balls白紙

b10cks the digestive tract (Fig. 3). Affected姐imals may thus suffer severe colic， causing them to 10se appetite and eventually die due to digestive diseases. F10ck mortality rates can be as high as 10% to 40%

(Hutyra et a l.1959; Shen， 2011). The wool‑biter.s are

巴asilyinfected by intemal parasites (Dwyer， 2008). A stomach worm， Haemonchus contortus， often thrives in the stomach of she巴p也at engage in woo1‑biting (Lynch et a .l1992). Simultaneously，出ewounds of victims are a1so easily infected by bacteria or 0也er. pathogens. In some areas， sheep血at extensively engage in woo1‑biting 10se their coat and die企omcold exposure

In也eear1y stages of woo1‑biting behaviour， sheep bite‑off the woo1企om other individuals， usually sta.rting合omthe rump or hind of back也atar^巴polluted by dust， soi1， or excrements. The afilicted animals may mt巴町upt仕出behaviourby moving away， escaping， o r. trying to reta1iate (Reinhardt， 2005). As也ea自icted anima1s receive mor巴biting合omthe woo1‑biters，出ey 10se their woo1 and appear as denude in the back area， which then spreads fOlward to the rest of the body，

Figure 2 A wool‑bitter is chewing woo .lA white hai巾all can obviously see inside its' mouth (see the arrowhead).

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HUANG AND TAKEDA

Figure 3: Some hai巾alls(A) and hair‑ropes (B) were found in the rumen from two wool‑biting sheep.

eventually resulting in their entire body denuded (Fraser and Fox， 1983). The shoulders and chest are also common t^紅getregions ofwool‑biters.

Adult sheep也at perform wool‑biting seems to appe紅 toinvolve only ewes (Reinhardt， 2005)， but it maybe because that adult male sheep are rarely rearing on flock indoor. The behavioural diversity of gender is need to be confmn. However， both mal^巴andfemale lambs have been observed to engage in this behaviour (Fig. 4). Moreover， it is believ巴d出atwool‑biting is associated with social dominance (Broom and Frasher， 2007). The sheep that receives the most wool‑biting are usually thos^巴withthe lowest hierarchy in th^巴flock，

姐 dthe individuals of出巴highesthierarchy often kept their fl^閃 cemtact

Although wool‑biting is usually consid巴reda sign of a lower level of welfare in sheep (Reinhardt， 2005; Vasseur etα .l2006)， the issue is rarely s加died.Until now， the cause of wool‑biting remains elusive. Farm m^組 agersbelieve出atstress causes出sbehaviour (e.g.， Simmons and Ekarius， 2010)， but the specific type of stress source was not be ascertained. Wool‑biting has also been consid巴redas a redirected behaviour related

Figure 4 Lambs of male (foreground) and female (background) were biting‑off wool form an adult ewe.

to a deficiency in fiber or roughage (Vasse町 etα .l 2006; Broom and Frasher， 2007). Furthermore， the deficiency of some minerals is also been believed to lead to wool‑biting.

Because the factors也at cause wool‑biting^{紅巳}

山水nown，it is hard to prevent or control this problem Th巴refore，it is worth to s凶nrnarizeand to reconsid紅

白巴白ldingsand theories on wool‑biting in sheep. 1n this paper， we reviewed the phenomenons of wool‑biting behaviour， and the possible factors企om some research巴s.

Behaviour backaround

Th巴reasonsor factors that induc巴wool‑bitingin housed sheep remain elusive. Possible factors include certain aspects of rearing management， and nutrient factors. And^，it is also have the possibility that combined interaction between various factors cause wool‑biting

Rearing management

Sheep are出emost sociabl巴farmanin1als， requ江mg close association with other members in也巴 flockto reduce stress， to facilitate normal behaviour， and to maintain proper manageme凶 andproductivity (Fisher and Ma仙ews，2001). Frum managers believe也at stress of indoor environment leads to wool‑biting， and releasing出esheep to出巴 pas^加re often stops this behaviour (Lynch et a .l1992)百1US，overcrowding in indoor pens is a potential stressor (L戸lch^巴ta l.1992; Broom and Frasher， 2007; Dwyer， 2008). Although Heath (1971) descri.bed也ateach ewe requ江esa space of appro氾mately12 ft2 (approx. 1.1 m ¥ but Broom and Frasher (2007) suggested that 10 sheep in a pen of approxirnately 20 m '"seems to be the lower lirnit to induce wool‑biting. Little is known about the effects of

油田sor behavioural change result企omovercrowding in sheep， but this feature leads to feather‑pecking and cannibalism in laying hens (Hughes and Duncan，

1972)， tail‑biting m pigs (Gonyou， 2001; Schroder‑Petersen and Simonsen， 2001)， and mor巴

aggression m rats (Mostafa， 2010). Because overcrowding is a stressor for captive anin1als and will result in some physical， endocrinal， or behavioural

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THE WOOL‑BITING OF SHEEP

problems (Lip^回p，1993; Grant and Abright， 2001; Al・Qud油，2012)，託mightbe possible伽 twool‑biting occ町sma曲目sfulenvironment， and白isbehaviour is reduced or disappears when the density of the flock is decreased or sheep are released to the pas加 e(Lynch et a .l1992).

Extemal parasites such as sheep keds and ticks reduce weight gain and cause anemia. These parasi^同 also cause irritation and itching， causing the sheep to rub， scratch， and iniure出世 wool.Some sheep bite themselves to relieve their suffering and occasionally become habitua1 wool‑chewers (Simmons姐 d Ekarius， 2010). Thus， it has the possibility白紙thesheep were habituate to chew wool，

組 dむyingto get wool form themselves or企omother flock members， resulting in也e development of wool‑biting habit.

A lack of environmental stimulation may also induce stereotypic behaviours in captive animals because也eyfeel bored. When grazing， sheep spend a lot of t訂ne feeding and ruminating. Some studies shown也atsheep in grazing take an average of 6.6 h 白rfeeding and 5 to 9 h for ruminating (Cory， 1927; A mold姐 dDudzinski， 1978). However， in s仕essful conditions， animals consume their daily food within a short period of time，組d血erest of the day is spent doing nothing. Environmental enrichment techniques have been developed to reduce wool‑biting in sheep but seemed to only delay也e appearance of this behaviour rather than prevent it (Bradley， personal comment). Cooper et al. (2005) suggested也atdividing the animals' meals into rations of smaller sizes may be an effective means of reducing oral stereotypic behaviours in stabled horses. However， Vasseur et al. (2006) found no differences in the occurrence of wool‑biting between high and low feeding frequencies in captive Merino sheep. They also considered that sheep consume their allocated food at once and出us presenting smaller portions will in result in less oral stimulation

Nutritions

Animals have some specific nutritional requirements and they balance their physical needs by choosing their food.百lemoose (Alces alces) has been repo此edto consume land plants血atcontain more calories to support their huge bodies， whereas也ey consume aquatic plants with low calories but high concen仕ationsof sodium for their daily requirement (Belovsky， 1978). Therefore， it is possible for herbivorous animals to detect specific minerals that 也ey need in surrounding plants. Because various minerals are essential for animals，也eyc佃 consume these by licking salt blocks in domestic conditions or feed on soil when grazing. However， sheep， cattle， and deer prey on b仕ds'eggs or chicks for calcium when 也isparticular element is lacking or insu伍cientin也e pas回re(Fumess， 1988; Nack姐 dRibic， 2005). The wool of sheep contains high amounts of sulfur and也us

也ey need to consume su伍cient sulfur for proper grow也 andmaintenance of也出 wool.It is也us possible也atsheep a伽mptto retrieve s叫白r企om也e wool of other individuals (Huang， 2001; Huang and Chen， 2001; Shen， 2011). Some researchers in China (e.g.， Huang and Chen， 2001; Shen， 2011) found出at when sheep does not find su伍cientsul白r也at也ey need in the pasture，也eywould attempt to retrieve this 企om姐 0也er so町ce such as wool， which is也m observed as wool‑biting (也eycalled it as "shimao zheng"， which means wool^圃ea住宅 S戸drome). Researchers considered出isphenomenon as a local nuむitional and metabolic disorder. Giving sheep CaS04 as a prescription or allowing them to graze in o血erpas加rescan cure也issyndrome.

However， some reports have shown 也at wool‑biting is associated with a deficiency in zinc but not sul白r姐 d by 0也er reasons. Zinc plays阻

important role in taste in animals， including human beings; animals with zinc deficiency may show ageusia， which leads to pica. A sheep with zinc deficiency usually presents with some complications such as alopecia， para‑and hyperkaratosis， woollesion， skin cracking， pica， and wool‑biting (Masters et a l.

1985; Suliman et a l.1988; White et a .l1994; Mozaffari and Dera1也shanf^紅，2007).Some researchers found that sheep engaged in wool‑biting have also been found to be zinc‑deficient (0枇etal. 1964; Suliman et a .l1988; Akgul et al. 2001). However， it is uncertain wh抽 er wool七itingis an outcome of zinc deficiency or a consequence of pica due to ageusia resulting企omzmc deficiency. Icen et al. (2008) reported that wool‑biting in sheep was associated with excessively high levels of zmc^，copper^{，組}diron.

Some reports suggested that certain of minerals or salt deficiency were considered to related to wool‑biting， because in the early phase of wool‑biting， sheep usually begin by biting wool企om也eparts of the rump or hind of another animals' back出atare polluted with soil or excrements. A♂ude of也e animal‑breeding technology of China has earlier reported that the levels of the minerals calcium， phosphorus， and molybdenum were excessively low in wool‑biting sheep. However， no reliable or robust evidence could associate白isbehaviour to the shortage or excessive levels of specific minerals. It may also be possible也atsheep 鮒emptsto find salt and not certain minerals (Bergeron et a .l2006). Salt deficiency has been associated with tail‑biting in pigs， although也lS condition does not fully explain how the abnormal behaviour initially develops (Fraser， 1987; Zonderland et al. 2011; Sonoda etα1.2013).

Another factor也athas often been discussed is fiber deficiency (Copper et al. 1995; Vasseur et a .l2006; Broom and Frasher， 2007). As a ruminant， sheep needs to consume su伍cientfiber to maintain the natural functions of their rumen and their appetite for rumination. According to Campion and Leek (1996)， rumination will cease within 8 days when sheep were

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HUANG AND TAKEDA

fed with concentrate only. Fiber may also offer sheep 也e satisfaction of oral stimulation by eating and ruminating these materials. Vasseur et al. (2006) described也atwool‑biting is a redirected behaviour of the unfulfilled need for stimulation of the sheep' s oral org姐 s.For most animals， fiber not only provides the oral stimulation but also也egut fill without excessive energy intake， which in turn reduces the motivation to feed (Robe目 et a .l1997)^阻 d the enac団側 of stereo勿picbehaviours in sow (Brouns， et a. l1994; Bergeron et a l.2000; Robert et a .l2002). Decreasing 也eproportion of fiber in food also increases the 企equencyof bar‑biting and chain‑chewing in heifers (Redbo and Nordblad， 1997)， as well as crib‑biting and wood‑biting in horses (McGreevy et a l.1995)

GONCLUSION

Stereo勿picbehaviour is 白血ledas a rep巴titiveact that is fixed in form and serves no obvious function: thus， wool‑biting should not be treated as a stereo勿plC be加、riourbut a redirect怠dbehaviour in some伺 ses because it seems to be associated with certain nu仕itional goals when fi吋 on a high ratio of concentrates.

Somβaspects such as farm management and nutrients seems to have been associated with wool^田biting;however， theseωnnot fully 'explain白e development of wool‑biting and why wool" was been chosen by sheep. Furthermore，也efactors也attrigger wool‑biting remain unclear， although multiple factors have resulted in血is behaviour. Wool‑biting is an abnormal behaviour and白紙 ne伊tively affi民ts也e welfare of創出nals.

FUTUREWORKS

Wool‑biting is a serious welfare problem in sheep; however，出ereis not su伍cientbackground knowledge on this behaviour. It is也us currently di伍cult to prevent or stop ltS occurrence目 Releasingsheep to也e pas加res or reducing flock density may solve the problem of wool‑biting， although抗isimpossible for every farm m釘lagersin some countries or釘easto provide pas旬res for their sheep. For othβr farms， reducing也edensity of a flock means to dβcreasUlg也e number of animals but not increasing血espace of pens， which may then be a cost‑ineffective approach to farm mana伊ment. Thus， an economical and effective me出odto con仕01wool‑biting is w創T佃おd.

One reaso司自atsh民pul pas加resdo not engage in wool‑biting behaviour may be也at白eyc血 domore f閃 dingand/or foraging， which are beha羽ours也ata domestic environment cannot provide. Since wool‑biting is very similar to normal feeding behaviours， sinlilar to血efeather‑pecking behaviour in laying hens， which is reduced if birds are given incentives也atelicit foraging behaviour (Aαni et. al.， 2000). Therefor百円也e relationship between 也IS abnormal behaviour and normalたedingbehaviours should be investigated.

Althou油田ceelement deficiencies were ob田町ed

m

^也êwôô^l^‑^bⁱ^tⁱⁿ^g^s^hêê^p^，^t^hê^rêⁱ^s^cû^r^rêⁿ^t^l^y^no p^rôô^f

that these deficiencies directly result in wool‑biting. These nu出tional relationships should也erefore be exantined in more detail. Deficiency in fiber is also a potential factor血atelicits wool‑biting， and increasing 也evolume or ratio of roughage in meals may be an e能ctivemethod of con仕ollingwool七iting. Broom and Frasher (2007) suggested也athay is ideal meal for sheep but 位awis also a useful fiber source to COll'仕01 wool‑biting. However， in the study conducted by Vasseur et al. (2006)， feeding sheep with s仕awfailed to completely prevent wool幽bitingbut only delayed its occ百四nce.So， it is possible也at紺awis not an ideal so町ceof roughage for sheep or，企oma nu出tional point of view， the required仕aceelements in s仕awwas lowerthan也atul也ecommon hay meal.

Although some reports have suggested 也at wool‑biting is related to social dominance in flocks， there is no concrete evidence也atsuppo此s也isopinion， and it also can not explain why wool同bitingceases when sheep are released to也epas加re.Vasseur et al. (2006) showed that some sheep perform or receive wool‑biting more由姐others，and也usthe relationship between wool‑biters and victims in terms of flock dominance should be investigated

The wool‑based objects in the rumen of wool‑biting sheep as showed in Figure 3 were found. However， information on its role in出e functioning of the digestive system of sheep or也eoptimal amount of this material to influence digestion in the rumen remains to be elucidated. This p紅tof issue is also worth to be studied

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