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494 EQUINE VETERINARY JOURNALEquine vet. J . (1992) 24 (6) 494-496

Comparison of two surgical methods for treatment of crib-biting in horsesA. HAKANSSON', P. FRANZENt and H. PETTERSSONRegional Animal Hospital, Box 22097,5-250 2 Helsingborg, Sweden.

IntroductionCrib-biting is a vice of horses which involves the perpetualswallowing of air (aerophagia) either by arching the neck or bygrabbing a fixed object (eg stable door) with its incisors (Tumeret al. 1984). It is generally considered to be caused by anxiety,inactivity and frustration, although the specific aetiology is notyet fully understood. Complications of this vice include a loss ofbodily condition, decreased ability to perform, alterations ofdigestive function, flatulent colic and wearing down of the upperincisors.Different methods of conservative therapy have beenattempted, including change of management, electrical aversiontherapy (Baker and Kear-Colwell 1974) and application of acribbing strap to prevent the horse moving its larynx. However,none of these techniques has any reliable effectiveness. A radicalmethod for surgical treatment was introduced by Forssell in 1926.This involves myectomy of the ventral musculature of the throat(ie mm. stemomandibulare, mm. omohyoidei, mm. stemohyoideiand mm. sternothyroidei). The method gives encouraging resultswith elimination of crib-biting, but leaves the horse with anoticeable defect on the ventral aspect of the neck (Hamm 1977;Fricker and Hugelshofer 1981). The operation is said to beinadvisable for horses under 3 years of age because of the risk ofmalformation of the trachea (Forssell 1926).In an attempt to overcome the deleterious effects of F orssell'soperation, a method of cutting the n. accessorious ventralis todenervate the mm. stemomandibulare was devised (Hamm1977). This method was later modified by Fraunfelder (1981 ) sothat it could be performed in the standing horse. Mixed successhas been achieved so far; Hamm (1977) and Monin (19 77)reported good results, whilst Firth (1980) and Owen et al.(1980) did not find it of any value (Table 2). In 1981 Fricker andHugelshofer reported another surgical method involving a lessradical myectomy (ie only partial resection of mm. omohyoidei,mm. sternohyoidei and rnm. stemothyroidei) combined with abilateral neurectomy of n. accessorius ventralis. This produced abetter cosmetic result than Forssell's method and horses youngerthan 3 years of age can be operated upon. This technique hasalso been reported on by Greet (1982), Huskamp et al. (1983)and Tumer et al . (1984). Fairly goo d results have been describedusing this method (Table 2).The objective of this study was to compare the long -term resultsof the two surgical methods used to correct crib-biting at theRegional Animal Hospital in Helsingborg, Forssell's method andthe combined myectomy/neurectomy method, since our clinicalexperience in the long term is at variance w ith previous results.*Present address: Department of Obstetrics & Gynaecology, Swedish University ofAgricultural Scien ces, Bo x 7039, -750 7, weden.+Present address: Department o f Medicine and Surgery, Swedish University ofAgricultural Sciences, Box 7018. S-75907, weden.

Materials and methodsCase materialDuring the periods 1958 to 1970 and 1980 to 1987, 228 crib-biting horses were presented to the Regional Animal Hospital inHelsingborg. The 117 horses in Group A were treated byForssell's method and the 11 1 in Group B by the combinedmyectomy/neurectomy technique.Operative proceduresThe horses were operated upon under general anaesthesia aftercasting with suxamethonium chloride (Celocurinchloride/KabiVitrum) or guaifenesin (Myolaxin vet./Chassot &Ciemayer). The anaesthesia was induced with thiopentonesodium (Pentothal natrium/Abbott) and maintained by inhalationwith halothane (HalothanM oechst), oxygen and nitrous oxide.The horses in Group A were operated upon as described byForssell (1926), involving resection of mm. omohyoidei, mm.stemohyoidei, rnm stemomandibulare (sternomaxillare) andfinally mm. stemothyroidei. The only exception from theschedule was that the skin incision from the thyroid cartilage tothe middle of the neck was extended to the distal third of the neckto make it possible to remove more of the muscles. In Group Bhorses the method described by Hu skamp et al. (1983) and Tum eret al. (1984) was used, including denervation of mm.stemo mand ibulare by resection of 10-12 cm of n. accessoriusventralis on both sides of the neck followed by resection of mm.omohyoidei and stemohyoidei and finally mm. stemothyroidei.Tetanus prophylaxis was given post-operatively and daily woundcare and antibiotic therapy were instituted. The owner wasrecommended to allow the horse to stand in a box (ie crib-bitingbox) with no manger or other protruding objects. It wasrecommended that feed be placed on the floor for at least 3- 4months after surgery.Follow-up details and statisticsFollow-up information was obtained by written reports and/orinterviews with the owners of the horse, 12-60 months afteroperation. The interviews were conducted according to apredetermined questionnaire. Information about breed, age andsex was obtained and other informative questions were:- For how long was the horse crib-biting before the operation?- Did the horse stop crib-biting after the operation?- If the crib-biting relapsed, when did it happen?- Do you think that the operation altered the exterior of the horse?- Does the horse have any crib-biting relatives?- Has the horse been in contact with any other crib-biting horse?- Did you place the horse in a box without protrusions (crib-bitingbox) after the operation, if so , for how long?

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EQUINE VETERINARY JOURNAL 495TABLE 1: Comparison of Forsells method (Group A) ar;d of the combined myectomy-neurectomy method (Group B) o correctcrib-bltina In horses

Group ANo. of horses Good results (10) Relapsed (%)

No. of horses 103 92 (89) 11 (11)warm blood 66 62 (94) 4 06)Thoroughbred 21 20 (95) 1 (5)Ponies 8 5 (63) 3 (37)Others 8 5 (63) 3 (37)

Swedish

Average ag e(years) 5.2 5.1 6.5Average durationof cribbing(months) 26 25 34

TABLE 2: Publlshed results of various surgical procedures orcrib-biting in the horseMethod No. of Good Improved Poor Follow-upReference horses result (10) (1.) result (1.) time (months )ForssellNeurectomy

Forssell 76 61 (80)Monin 73 39 (53)Harnm 150 90(6)Monin 6 3 (50)Oweneta/. 3 - -Frauenfelder 3 1 (33)Firth 8Fricker et a /. 10 8 (80)Greet 9 7 (78)Huskampeta/ . 28 26 (93)Tuner eta/. 35 20 (57)

- _Myectomy/Neurectomy

11 (31)

15 (20)20 (27)30 (20)3 (1002 (33)_ _8 (100)

0.53-1 843-20>512

Comparison was made within the groups between horses w ithgood operation results and horses relapsing in any grade andbetween the groups (between the two operation methods), withregard to breed, age and duration of crib-biting before operation.The cosmetic result of each operation method was also regarded.Statistical calculations of the responses received to thequestionnaire were done with the Mann-Whitney U-test and thechi-square method. The models are described by Campell (1974).ResultsReplies were obtained for 103 horses (88%) in Group A and 103(93%) horses in Group B. The follow-up results from surgery inGroup A showed that most of the horses stopped crib-biting(Table 1). The others relapsed between 8 days and 1 year, with anaverage of 3 months post-operatively. In Group B, only halfresponded favourably. Some horses (32.5%) resumed crib-bitingof the same intensity immediately after the operation (14%), andthe rest after a more extended period (18.5%). Some horses thatresumed crib-biting (18.5%) appeared to be less severely affectedand were recorded as having partial improvement (Table I ) . Theaverage period before the return of crib-biting was 8 months,varying between 2 weeks and 30 months. The Forssellsprocedure gave significantly better results (P

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EQUINE VETERINARY JOURNA Lpositions of nerve ramifications if the amount of nerve tissueresected is less than 6.8 cm, but they did not discuss thepossibility of regeneration.In both groups of horses in the present study conformationalalterations in the ventral neck were observed but only in a smallnumber of the patients. For Group A we expected a greateramount of conformational alterations. The explanation of theunexpected good results may be due to the fact that i f the horseceases to crib-bite the owner is less aware of the alteration than ifthe horse continues to crib-bite. Young horses and horses with ashort history of crib-biting are the most likely to provide a goodoperation result (Table I ) . These results may be due to the factthat these horses do not have the chance to develop strong ventralneck muscles or to strengthen the pattern of behaviour.Swedish Warmblood horses dominated the breeds in this study,and this is also true for the rest of the case load in the clinic.Standardbreds are poorly represented in the stud y, despite the factthat this breed makes up about 17% of the clinic case load.Although Thoroughbreds make up a smaller percentage of all theclinical cases, the breed is over-represented in comparison withother breeds. Disparity amongst the breeds may have its origin indifferences in temperament, constitution and managem ent.The imcomplete data and low response rates do not allow anyconclusions to be drawn on the heritability of crib-biting. Thestabling of the horses in crib-biter boxes post-operatively did notseem to have any b eneficial effect. Statistically , there was nodifference between ordinary stabling and that in the crib-biter boxes.However, it is well known that any available surface that offers asturdy hold can lead to crib-biting. It is not clear whether ownersclaiming to p rovide crib-biter boxes really did so effectively.The conclusion of this study is that both surgical methods hadsome disadvantages. The Forssell's operation gives better long-term clinical results but can lead to a conformational deformity onthe ventral aspect of the neck. This was found to be only a minorcomplication in this study. The combined myectomy/neurectomy

method involves a much higher risk of relapse, especially i nThoroughbreds. This study also proves the importance of anextended follow-up period to reveal potential relapses.A combination of these two methods is currently being testedat a number of clinics. The results are yet to be analysed.AcknowledgementWe thank Professor Leo B. Jeffcott for constructive criticism ofthe manuscript.ReferencesBaker, G.J. and Kea r-Colw ell, J. ( 1974) Aerophagia (=w indsu cking ) and aversionCampbell. R.C. ( 1974) Sruiisrir's i f Biolog isrs. Cambridge University Press,Firth, E.C. ( 1980) Bilateral ventral accessory neurectomy in windsucking horses.Forssell. G. (1926) The new surgical treatment against cribbiting. V d .J. 82.538-548.Frauenfelder. H. (19 81) Treatment of crib-b iting: A surgical approach in the standingFricker. C. and Hugelshofer. J. (1 98 1) Neurektomie verbunden mit M yekto mie als

therapy in the horse. Pro( , .A m . Ass. Equine Prucr. 127-129.Cambridge.Vrr. Rrc. 106. 30-32.

horse. Eqirinr w r . J . 13.62-63.Alternative zu der klassische Kopperoperation nach Forssell. S c h e i : . . A d i .Tierheilk. 123. 2 19-22 .

Greet, T.R.C. ( 1982) Windsucking treated by myectomy and neurectomy. Eqirinrw r . ./. 14. 299-30 I .

Hamm. D. (1977) A new surgical procedure to control crib-biting. P r w . An!. Ass .Equine Prucr. 23,301-302.Huskamp. B., Henschel. E. and Arenhoevel. H . (19 83) Technik und Ergebnisse einermodernen Kopperoperation.Der Pratrisckr Tierurzr.64. I 10-119.Monin. T. 1977) In discussion on the paper by Hamm. P r w . Am.. Ass. Eqiri~irPrucr. 23.302-303.Owen, R., McKeating, F.J. and Jagper. D.W.198 0) Neurectomy in windsuckinghorses. Vef. Rec. 106, 134-135.Turner, AS ., Whit e, N . and Ismay. J. (198 4) Mod ified Forssell's operation for crib-biting in the horse../.Am . wr.nwd. Ass . 184. 309-312.

Corrections Volume 24 (NO.5 ) , September 1992We regret that problems during production of this issue led to some figures being reproduced below thestandard required. The most severely affected figures were those of Watson et al. reproduced below, andMeyer et al. and Dyson and Kidd to be reproduced in Volume 25 (No. l ) , anuary 1993.Watson, T.D.G., Burns, L., Love, S., Packard, C.J.and Shepherd, J . Plasma lipids, lipoproteins and post-

heparin lipases in ponies with hyperlipaemia. pp 341-3462

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