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Study of the behaviour, digestive efficiency and gut transit times of crib-biting

P. D. MCGREEVY, A. J. F. WEBSTER, C. J. NICOL

The spontaneous behaviour and the apparent digestibility of dry matter and fibre and transit times of digesta were compared in four normal horses and four crib-biters. A technique was developed for measuring total gut transit times (TGTT) by using single-stool analysis of the passage of radio-opaque polyethylene markers. Longer TGTT were recorded in the crib-biters than in the normal horses but the orocaecal transit times did not differ. The crib-biters rested less than the normal horses.

CRIB-BITING, a repetitive and invariant oral behaviour of ioural part of this study. The study also aims to establish horses, creates a transient distension of the cranial oesopha- whether horses which perform oral stereotypies have a dif- gus which, it has been suggested, may have an effect on sati- ferent digestive physiology from normal horses. As the first ety receptors (McGreevy and others 1995). The function of part of the alimentary tract, the mouth is the site of process- crib-biting remains uncertain and there is minimal evidence ing activity that can affect the physiology of the entire diges- of it reducing stress (McGreevy and Nicol 1998a). tive tract (Stevens 1977). Intestinal transit time was selected Circumstantial evidence which might link oral stereotypies as a relatively non-invasive method by which the digestive with nutritive behaviour includes the effect that diet has upon function of the horses might be studied. It is defined as the the intensity of the stereotypies (Marsden 1993), the tempo- time taken for a marker to pass through the gut. Historically, ral association between bouts of and the ingestion a variety of markers have been used, including glass beads of concentrate feed (Kusunose 1992), and the suggestion that (Alvarez and Freedlander 1924), ball-bearings (Burnett 1923) more palatable food elicits more ofthe anomalous behaviour and radioisotopes (Hansky and Cornell 1962). However, all (Dodman and others 1987). The functions of other oral single marker methods rely on the continuous collection of behaviours have been elucidated only by elaborate physio- faeces and have serious limitations in practice. The determi- logical investigations. For example, De Passille and others nation of the transit times of two species of radio-opaque (1992) used indwelling portal vein catheters to show that markers in single faecal samples is a technique which has been apparently functionless non-nutritive sucking behaviour developed in human medicine (Cummings and Wiggins contributes to postprandial hormonal changes in calves. 1976) and could have useful clinical applications in equine Recently, gut transit studies have been reported in horses gastroenterology. transiently deprived of the opportunity to eat hay and/or Since one factor that affects the passage of particles crib-bite (McGreevy and Nicol 1998a). These showed that through the gut is specific gravity (Hoelzel 1930), it is impor- there was an increase in the orocaecal transit time (OCTT) of tant that the specific gravity of radio-opaque polyethylene crib-biters when they were deprived ofthe opportunity to eat markers is comparable to that of faecal residues. The specific and crib-bite. gravities of the radio-opaque pellets used in this study were Although the possible function of crib-biting remains in the range 1-3 to 1 6 (Cummings and Wiggins 1976), the uncertain, the owners of crib-biters persist in attempting to density of cellulose, which is the main faecal residue in her- prevent the behaviour because of its perceived deleterious bivores (West 1974). effects on the crib-biters' health and appearance (McGreevy To provide specific data on orocaecal activity, a minimally and Nicol 1998b). Crib-biting in horses is traditionally asso- invasive measure of the OCTT involving the microbial break- ciated with 'unthriftiness' or failure to maintain bodyweight down of sulphasalazine was used. The technique, which (Hayes 1968). Possible reasons why crib-biters should main- involves the detection of a breakdown product, sulphapyri- tain less bodyweight than normal horses on an equivalent dine, in sequential plasma samples, has recently been adapted ration include its behavioural effects, including the expendi- for use in horses (McGreevy and Nicol 1998a). Veterinary Record (2001) ture of energy in performing the activity, and the possibility 148, 592-596 that they might eat less or waste food by dropping it out of their mouths (Fraser 1992). There may also be digestive con- MATERIALS AND METHODS P. D. McGreevy, BVSc, sequences, for example, long-term crib-biting may reduce the PhD, MRCVS, digestibility of food because the resultant wear may Horses A. J. F. Webster, MA, result in the food being less well masticated. Eight thoroughbred geldings of similar body condition were VetMB, PhD, MRCVS, The aims of this study were to determine whether four used. Their bodyweights ranged from 491 kg to 648 kg. Four C. J. Nicol, BA, PhD, crib-biters were less able to maintain bodyweight than four were crib-biters and four had never displayed the behaviour; Department of Clinical normal horses and, if so, why. The spontaneous behaviour, the mean (sd) starting weights of the normal and stereotypic Veterinary Science, and the apparent digestibility of dry matter (DM) and fibre, horses were 5511 (33.9) kg and 533 (3.58) kg, respectively. University of Bristol, and transit times of digesta in the four normal horses and the They were bedded on woodshavings in concrete pens (4.5 x Langford House, four crib-biters were compared. A technique was developed 4-2 m) with rendered walls to a height of 1-4 m, with 6 cm Langford, Bristol for measuring total gut transit times (TGTT) by the analysis diameter tubular metal railings set 50 cm above the wall. Each BS18 7DU of the passage of radio-opaque polythene markers from pen had an outside portion (4-8 x 4 5 m) with walls of the single samples of faeces. same design and an automatic watering device. Visual, tac- Dr McGreevy's present Estimates of the number of crib-bites performed in a day tile and olfactory contact between horses was possible over address is Department of vary with the individual (Dodman and others 1987, the railings. Animal Science (B19), Kusunose 1992, McGreevy and Nicol 1998b), and the time The study lasted six weeks. In the first week the horses were Faculty ofVeterinary occupied varies accordingly but some horses spend over eight treated with anthelmintic and acclimatised to the stables. Science, University of hours per day crib-biting (McGreevy and Nicol 1998b). The They were then introduced to the test diet, and gut transit and Sydney, NSW 2006, consequences of this activity are considered in the behav- behavioural measurements started in the fourth week. Australia

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first morning, and 300 R3 markers on the second. The Rl markers were 2 mm long and 0 75 mm in diameter, and the Time since ingestion (t) 8 16 24 32 40 48 56 64 72 80 88 96 104 Total R3 markers were 0 75 mm long and 2 mm in diameter. These lengths of hollow plastic tubing were mixed in an aqueous Number of markers (s) 0 4 33 47 22 30 17 10 13 8 14 5 0 203 paste made from approximately 40 g low protein cubes. This txs 0 64 792 1504 880 1440 952 640 936 640 1232 480 0 9560 mixture was loaded into 60 ml syringes and administered like t Time from ingestion of markers to time of collection (hours), s Number of markers in each of the an oral anthelmintic. 13 collections Bedding was removed from the loose boxes six hours later. The following results from one type of marker in one horse are provided as a working example: For verification purposes, the total faecal output ofeach horse (t xs)- 9560 = was then collected every eight hours for 96 hours, and each 1(s) 203 47-1 hours sample was oven dried at 80°C for 48 hours, weighed and radiographed in polyethylene bags. The radiographs were then examined and each species of marker excreted during Feed each eight-hour period was counted. At the beginning of the trial, the horses were being fed 10 kg The mean transit time (Cummings and Wiggins 1976) of of hay per day. The test feed was introduced by giving 2 kg each type of marker through the alimentary tract was calcu- with 3 kg ofhay twice daily. Over the next seven days, the test lated from the mean ofthe analyses ofthe individual samples feed component was increased to 5 kg twice per day until it by using the equation replaced the hay ration completely for the following five weeks. The test feed was a commercial 'complete' diet for TGTT = S(t£(s)x s) maintenance (PhD Diets) based on a coarse mixture ofcereals and chopped forage and formulated to provide a balanced where t is the time from the ingestion of the markers to the supply of nutrients and sufficient long fibre to promote time of collection, and s is the number of markers in each healthy digestion. Its composition was as follows: fibre 21-0 sample. Table 1 gives an example of the calculation. per cent, protein 13-0 per cent, ash 7-2 per cent, oil 3 0 per cent, calcium 1-6 per cent and phosphorus 0 9 per cent. The Determination of ocrT horses were fed at 09.30 and 16.30, and took between 60 and The horses were given a paste of 26 g of sulphasalazine 90 minutes to consume their ration which was designed to (Salazopyrin; Kabi Pharmacia) milled with 30 5 g of mint provide 1 MJ digestible energy/kg bodyweight0 75; approxi- sweet (Polo; Nestle Rowntree) by mouth and the first blood mately 1-5 times maintenance requirements. samples (7 ml in oxalate fluoride) were withdrawn via indwelling jugular catheters. Sequential samples were taken Determination of TGTT with Portex markers every hour for the next six hours. Sulphapyridine was Radio-opaque barium sulphate-impregnated polyethylene detected by high performance liquid chromatography (HPLC) markers (Portex) were administered orally on two consecu- as described by McGreevy and Nicol (1998a). In all the assays, tive mornings. Work in human beings (Cummings and the threshold offirst appearance was set at the point at which Wiggins 1976) has shown that these markers do not change the ratio of sulphapyridine to the internal standard alimentary activity. Giving a single dose of a marker and (sulphamethazine) reached 0-02. recording its appearance in the faeces is the most usual means ofestimating the time taken for food residues to pass through Determination of digestibility the gut. In studies on humans it is suggested that there is Chemical measurements were carried out on both feed and increased accuracy in the measurement of single stool tran- faeces. Measurements of DM, organic matter (OM), gross sist times when two markers are used (Davignon and others energy (GE), crude protein (cp), acid detergent fibre (ADF) and 1968, Cummings and Wiggins 1976). By using two markers neutral detergent fibre (NDF) were made using the official ofdifferent shapes the aim was to determine gut transit times methods of AOAC (AOAC 1995). from the analysis of a single faeces sample. A pilot study in Faecal analysis was performed on all faeces passed in the 10 horses showed that there were no significant differences in fourth and fifth week of the study. The faeces were dried in a the transit characteristics of the two species of marker and forced draught oven as described above, milled and sub- that they were therefore appropriate for the development of sampled before DM analysis. Further grinding through a 1 mm the method. Having established that TGTT can be assessed screen was followed by determinations ofOM, GE, CP, ADF and accurately, the technique was used to identify any functional NDF, as above. differences between the normal and the crib-biting horses. The horses were weighed every 14 days on a walk-on Three hundred RI markers were given to each horse on the weighbridge. Behaviour 400 -U- Crib-biting horses (n=4) Behaviour was recorded for 10 days during the final 14 days (DE - Normal horses (n=4) of the study. Pairs of horses were scan sampled alternately a) c every 30 seconds for two hours in the afternoon and for a fur- 300 ther two hours the following morning. Cribbing, eating, drinking, self-grooming, interacting with neighbours, + 0 -s rubbing against the wall of the box, pacing the box, resting, D D 200 defaecation and urination were all recorded. cca

co °Lcn 0) RESULTS ac 100 E cu TG1T FIG 1: Faecal output of c 2 0 The total mean number of RI markers retrieved was 171*12 gut transit markers (10-09) and for R3 was 164 12 (8-01). This gave mean retrieval 0 25 50 75 100 (Ri +R3) in horses on rates for markers RI and R3 of 55 and 51 per cent, respec- the complete diet TTime since administration of markers (hours) tively. Mean transit times for the two markers (43 05 [2-29]

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06 * Crib-biting horses (n=4)

- - - : CDc0 0.6 -- Normal horses (n=4) Latency for ratio Latency for ratio 'a Crib-biter to reach 0-02 Normal horse to reach 002 E 04 0) 1 180 5 60 , 2 120 6 300 ._ 0-3- 3 60 7 120 0) 4 60 8 60 E 0.2- Mean e) 105 minutes (28.72) Mean (se) 135 minutes (56.79) COco o 0-1 Ir- FIG 2: Mean bioavailabilty of sulphapyridine in the hours for RI and 38-96 [1-65] hours for R3) were not signif- 0 100 200 300 400 500 plasma of horses on the icantly different (Wilcoxon signed-rank test, P=0-0687). Time since administration of sulphasalazine (minutes) complete diet. Bars = se Therefore, the mean times for the transit of both markers in the two groups of horses were compared with a Mann- Whitney test. Normal horses had significantly shorter mean significantly less time (33-25 [2-93] per cent) (Mann-Whitney TGTTS (37-6 [2-39] hours) than crib-biters (43-6 [1-56] hours) test, P<0-05) resting than normal horses (48-56 [5-44] per (P<0-05) (Fig 1). cent). There was a non-significant positive correlation between the number ofvisits to the watering device and num- OCiT ber of bouts of crib-bites observed (correlation coefficient The time to first appearance (<0-02 sample:standard) varied 0-485). No food refusals were observed. from 60 to 300 minutes. The appearance ofsulphapyridine in the plasma is represented in Fig 2. The mean time to first appearance for stereotypic horses (105 [28-72] minutes) was DISCUSSION not significantly different (Mann-Whitney test, P=0-8852) to that of normal horses (135 [56-79] minutes) (Table 2). Even This experiment shows that radio-opaque polyethylene pel- though this difference did not achieve statistical significance lets can be useful as particulate faecal markers in the horse it was, in relative terms (105/135=0-78), greater than that because they are unabsorbed, non-toxic, easy and safe to observed for TGTT (37-6/43-6=0-86). measure. The key to any such adaptation would involve a pre- diction of when single stools would be passed with a repre- Faecal analysis sentative number of both types of marker. This time period The mean daily dry-weight faecal outputs for the normal and would be influenced by the type ofequid being studied (Hintz stereotypic horses were 3-06 (0-263) kg and 2-91 (0-072) kg 1990, Cuddeford 1995), its diet (Fonnesbeck 1969), its stress (unpaired t test, P=0-6014), respectively. The mean (se) per- response (Enck and others 1989) and possibly the amount of centage digestibilities for crib-biters and normal horses are exercise it receives (Orton and others 1985, Pearson and shown in the Table 3. No significant differences emerged. Merritt 1991). An observer would have to remain with the subject during this period and record the time of each defae- Weight changes cation. A considerable increase in the number of markers Both normal and stereotypic horses put on weight during the would also be required to increase accuracy before single stool experiment. Mean finishing weights for the normal and analysis could be relied upon in gut transit studies. stereotypic horses were 583-25 (37-99) kg and 551-5 (3-33) kg, The rates of retrieval were low compared with those of respectively (Fig 3). Mean weight changes over the six weeks other particulate markers used in previous equine gastro- for normal and stereotypic horses were 32-12 (5-89) kg and enterological studies (83 per cent [Van der Noot and 18-5 (3-8) kg, respectively. The normal horses therefore Gilbreath 1970], and 94 per cent [J. M. Hunt, unpublished showed a tendency to put on more weight, but this was not observations]). This may be due to poor resolution of the statistically significant (unpaired ttest, P=0-0865). Expressed radiographic image through the bags offresh faeces (often the as a percentage oftheir mean starting weights, these increases faeces were voluminous and more than 16 cm in depth) or were more alike: 5-78 kg (normal) and 3-47 kg (crib-biters), retention of the markers in the intestine. Coprophagia may and again the unpaired t test showed that the difference was non-significant (P=0-0701). Behaviour 20 The percentage oftime spent in 10 activities are shown in Fig 4. There was a trend (Mann-Whitney test, P=0-0814) for crib- biters to spend less time (18-82 [1-93] per cent) eating than -02) normal horses (32-89 [5-35] per cent). The crib-biters spent -0 .0 C Co 0) 0) c M Crib-biting horses (n=4) .-C 0 Normal horses (n=4) Crib-biers Normal horses Mann-Whitney C Measremewt (n-4) (n=4) P value 01) matter 56&38 (6.03) 53-74 (4.39) -7728 Grossener 64.355 6401 (1-68) 0-8845 Crd pr 4616 (1 4 (1 0-5637 FIG 3: Mean weight Aciddetergent fibre 034-13 (04 34-06 (3-31) 0-3865 in horses 0 2 4 6 8 changes on Neur deegn fibre 45.72(0-6 45.05 (2.43) 0-2482 the complete diet. Time on diet (weeks) Bars = se

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60 * Crib-biting horses (n=4) various components of the diet. Therefore, any unthriftiness * Normal horses (n=4) in crib-biters is unlikely to be related to changes in digesta motility. The apparent retention of ingesta in the caeca of 50 crib-biters could reflect an imbalance in their gut flora, per- haps as a result of hindgut acidosis (Nicol 1999).Among other - possible functions, crib-biting may represent an adaptive .2 40 . attempt to reduce transit times; this is effective in the foregut C.)0 but less effective in the hindgut. co 30 It is interesting to consider these results in the light of pre- C vious studies which showed an increase in the OCTT of crib- C biters when deprived of the opportunity to eat and crib-bite C) a cn 20 (McGreevy and Nicol 1998a). It is possible that crib-biting (D E horses have a general tendency to have slow transit times, which they usually overcome by crib-biting, and it is only 10 when they are prevented from crib-biting or placed on an extreme all-concentrate diet that this latency, which is usually masked, becomes apparent. FIG 4: Percentage of 0 In this study, attempts to select horses of similar body- time spent on each c -2 -~e a)~ E 0 weight may have introduced differences in metabolic require- behaviour by crib-biting o horses and normal ments between experimental and control animals. This is a) IC horses on the complete co because, although bodyweights can be more accurately mea- diet. * Significantly 0 sured than body condition, any pre-existing differences in different. Bar = se Behaviour body condition would be reflected in differing ratios oftissues, for example, muscle to fat. Therefore, an already unthrifty crib-biter, with a greater proportion of muscle to fat than a have reduced retrieval rates but this seems unlikely because control horse, would require more energy for maintenance. the appearance of markers in the faeces in all trials followed Although there were no significant differences in the similar patterns. This could only have occurred if all the weight changes during the study, there was a trend towards horses ate their own faeces at only set times on many occa- lower weight gains in the stereotypic animals. WAhile this sions. The degree of intestinal retention that would be experiment was long enough to investigate the digestibility of required to explain the low retrieval rate is inconsistent with the novel diet, it was too short to expose the long-term con- the results of previous equine gastroenterological studies sequences of crib-biting. The absence of ridden exercise in which have used other particulate markers (for example, this experimental design may have contributed to energy con- cerium and chromium mordanted fibre [Uden and others servation and therefore weight gain. However, in practice, 1980]) and reported retrieval rates of more than 95 per cent. exercise reduces the time available for stereotypical behaviour Furthermore, because the disappearance of markers after 100 and may fatigue horses to the extent that they are more likely hours was apparently absolute, the gradual excretion of tem- to rest than stereotype (Kiley-Worthington 1987). Working porarily retained particles seems to have been ruled out. horses with stereotypies may have greater maintenance Problems with imaging during radiography would appear to requirements than normal horses. In rare cases, crib-biting be the most likely explanation of the fate of the 'lost mark- may be associated with such profound incisor erosion that the ers'. Drying the faeces to reduce the volume that has to effective prehension oflong fibre may become compromised. be radiographed would enhance resolution and therefore The behavioural studies have shown that crib-biters rest detection rates. less than normal horses. This may be an important cost for Despite the disappointing rates of marker retrieval, there horses that expend energy when crib-biting, which would was consistency in mean transit times between the first and otherwise have been conserved at rest. The tendency for crib- second trials. Transit times in the region of 40 hours are con- biters to spend less time eating is also likely to contribute to sistent with those quoted by other authors using chromium a relative energy deficit and, therefore, unthriftiness in horses mordanted fibre (Pearson and Merritt 1991, Cuddeford 1995) on a critical plane of nutrition. and inorganic particulate markers (Van der Noot and others In the course of the six-week trial, occasional displays of 1967, J. M. Hunt, unpublished observations). lignophagia, coprophagia and intraspecific aggression were The insignificant differences in transit times between the two observed in the 21 or more hours per day when the horses markers may have arisen because of the different shapes which were not feeding. It has been suggested that these behaviours caused RI to trap pockets of air more easily than R3. This may indicate feed-related frustration (Rees 1984, Crowell-Davis have allowed R1 to float along the gas/fluid interface quicker and Houpt 1986, Ralston 1986, Kiley-Worthington 1987, than R3 which was in the particulate phase of the ingesta. Fraser 1992). It seems, therefore, that while being nutrition- Longer TGTTS were found in crib-biters compared with ally sufficient for maintenance, the 'complete diet' being fed normal horses, while OCTTs did not differ. This suggests that to the horses in this trial was failing to meet their behavioural the difference in TGTT reflects prolonged hindgut and not needs. foregut activity. Therefore, these data may indicate that oro- caecal digestion in crib-biters is less efficient. Thus, it may be that, because ofpoor mastication and emulsification, fibre has ACKNOWLEDGEMENTS to be retained in the large intestine for longer than normal. Given their longer TGTTS, one would predict better apparent Morley Badman and Susan Aston are thanked for their help digestibility in crib-biters compared with normal horses. in caring for the horses in this study. Dr Michelle Hyde and Crib-biting might be a response to a disorder of digestion that Professor David Fraser are thanked for their comments on is associated with prolonged TGTT and possibly OCTT. early drafts ofthis manuscript. The authors are grateful to Dr However, the motivation to crib-bite in these circumstances Frances Barr and Jeanne Latham who made radiographic should not be taken to imply that the strategy is successful. equipment available for this study. The digestibility assays Ultimately, however, these differences in gut function do not were conducted by Mike Kitcherside. This work was funded manifest themselves in lower percentage digestibilities for the by the Horserace Betting Levy Board and the RSPCA.

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References Management and Training. London, J. A. Allen. p 265 AOAC (1995) Official Methods of Analysis of the Association of Official KUSUNOSE, R. (1992) Diurnal pattern of cribbing in stabled horses. Japanese Analytical Chemists. 16th edn. Washington DC, AOAC Journal ofEquine Science 3, 173-176 ALVAREZ, W. C. & FREEDLANDER, B. L. (1924) The rate of passage of food MCGREEVY, P. D. & NICOL, C. J. (1998a) Behavioural and physiological con- residues through the bowel. Journal of the American Medical Association 83, sequences associated with the short-term prevention ofcrib-biting in horses. 576-580 Physiology and Behaviour 65, 15-23 BURNETT, F. L. (1923) The intestinal rate and the form of faeces. American MCGREEVY, P. D. & NICOL, C. J. (1998b) Methods for the prevention of crib- Journal ofRoentgenology 10, 599-604 biting - a review. Equine Veterinary Journal Supplement 27, 35-38 CROWELL-DAVIS, S. L. & HOUPT, K. A. (1986) Techniques for taking a behav- MCGREEVY, P. D., RICHARDSON, J. D., NICOL, C. J. & LANE, J. G. (1995) ioural history. Veterinary Clinics ofNorth America: Equine Praccice (Behaviour) A radiographic and endoscopic study of horses performing an oral stereo- 2,507-518 typy. Equine Veterinary Journal 27,92-95 CUDDEFORD, D. (1995) Are there differences between horses and ponies? In MARSDEN, M. D. (1993) Feeding practices have greater effect than housing International Conference on Feeding Horses. Northamptonshire, Dodson practices on the behaviour and welfare of the horse. Livestock Environment & Horrell IV. 4th International Symposium of the American Society of Agricultural Engineers, University of Warwick, CUMMINGS, J. H. &WIGGINS, H. S. (1976) Transit through the gut measured Coventry. pp 314-318 NICOL, C. J. (1999) Stereotypies by analysis of a single stool. Gut 17,219-223 and their relation to management. In Proceedings of the BEVA Specialist Days on Behaviour and Nutrition. Eds P. A. DAVIGNON, J., SIMMONDS, W. J. & AHRENS, E. H. (1968) Usefulness of Harris, G. M. Gomarsall, H. P. B. Davidson, R. E. Green. Newmarket, chromic oxide as an internal standard for balance Equine studies of formula-fed Veterinary Journal. pp 11-14 patients and for assessemnt of colonic finction. Journal of Clinical ORTON, R. K., HUME, I. D. & LENG, R. A. (1985) Effects of exercise and level Investigation 47, 127-138 of dietary protein on digestive function in the horse. Equine Veterinary DE PASSILLE, A. M. B., METZ, J. H. M., MEKKING, P. & WIEPKEMA, P. R. Journal 17,386-390 (1992) Does drinking milk stimulate sucking in calves? Applied Animal PEARSON, R. A. & MERRITT, J. (1991) Intake, digestion and gastro-intesti- Behaviour Science 34,23-26 nal transit time in resting donkeys and ponies and exercised donkeys given DODMAN, N. H., SHUSTER, L., COURT, M. H. & DIXON, R. (1987) ad libitum hay and straw diets. Equine Veterinary Journal 23, 339-343 Investigation into the use of narcotic antagonists in the treatment of a stereo- RALSTON, S. L. (1986) Feeding behaviour. Veterinary Clinics ofNorth America: typic behaviour pattern (crib-biting) in the horse. American Journal of Equine Practice (Behaviour) 2, 609-621 Veterinary Research 48, 311-319 REES, L. (1984) The Horse's Mind. London, Stanley Paul. p 199 ENCK, P., MERLIN, V., ERCKENBRECHT, J. F. & WIENBECK, M. (1989) STEVENS, C. E. (1977) Comparative physiology of the digestive system. In Stress effects on gastrointestinal transit in the rat. Gut 30,455-459 Dukes' Physiology of Domestic Animals. Ed. M. J. Swenson. London, Cornell FRASER, A. F. (1992) The Behaviour of the Horse. 1st edn. Wallingford, CAB University Press. pp 224-226 International. pp 214-216 UDEN, P., COLUCCI, P. G. & VAN SOEST, P. J. (1980) Investigation of FONNESBECK, P. V. (1969) Partitioning of the nutrients of forage for horses. chromium, cerium and cobalt as markers in digesta. Rate of passage studies. Journal ofAnimal Science 28,624-633 Journal ofthe Science ofFood and Agriculture 31, 625-632 HANSKY, J. & CORNELL, A. M. (1962) Measurement ofgastrointestinal tran- VAN DER NOOT, G. W. & GILBREATH, E. B. (1970) Comparative digestibil- sit using radio-active chromium. Gut 3, 187-188 ity ofcomponents of forages by geldings and steers. Journal ofAnimal Science HAYES, M. H. (1968) Veterinary Notes for Horse-Owners. London, Stanley 31, 351-355 Paul. p 655 VAN DER NOOT, G. W., SYMONS, L. D., LYDMAN, R. K. & FONNESBECK, HINTZ, H. (1990) Digestion in ponies and horses. Equine Practice 12,5-6 P. V. (1967) Rate of passage of various feedstuff through the digestive tract HOELZEL, F. (1930) The rate of passage of inert materials through the diges- of horses. Journal ofAnimal Science 26, 1309 tive tract. American Journal ofPhysiology 92,466-497 WEST, R. C. (1974) Handbook of Chemistry and Physics. 54th edn. Cleveland, KILEY-WORTHINGTON, M. (1987) The Behaviour of Horses: In Relation to CRC Press

Evaluation of the dosage of ivermectin in falcons

M. LIERZ

Twelve groups of falcons, each containing three female gyrfalcon-peregrine falcon hybrids (Falco rusticolus x Falco peregrinus) were injected intramuscularly with a single dose of ivermectin ranging from 0-2 mg/kg to 1 1 mg/kg bodyweight, and a control group was injected with water. Doses of ivermectin between 0-2 and 5 mg/kg failed to produce clinical signs of illness in the birds. Four birds which received either 6, 7 or 8 mg/kg showed slight clinical signs, and all the birds receiving 9 to 11 mg/kg showed more or less severe clinical Veterinary Record (2001) signs of anorexia, apathy and sedation. Slight changes in the mean plasma activities of aspartate 148, 596-600 aminotransferase, alanine aminotransferase and alkaline phosphatase (AP) were detected in the group dosed with 5 mg/k& and higher dosages caused marked changes in these enzymes as well as in the mean plasma M. Lierz, DrMedVet, activity of lactate dehydrogenase. The mean activity of AP decreased, and the activities of the other enzymes MRCVS, Abu Dhabi increased. A dosage of 2 to 3 mg/kg ivermectin is recommended as a safe and effective antiparasitic drug for Falcon Research Hospital, falcons and it has been used successfully to treat infestations of Serratospiculum species. PO Box 77, Abu Dhabi, United Arab Emirates IVERMECTIN, administered either orally, topically or by contains 80 per cent 22,23-dihydroavermectin Bla and 20 injection, has been used for the treatment of mite and nema- per cent 22,23-dihydroavermectin Blb (Loescher and oth- Dr Lierz's present address tode infestations in wild and domestic birds. Ivermectin is ers 1991). It increases the potential of the inhibitory neu- is Nonnenpfad 5,49074 a product of the actinomycete Streptomyces avermitilis, and rotransmitter gamma-aminobutyric acid (GABA), which Osnabrueck, Germany

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Study of the behaviour, digestive efficiency and gut transit times of crib-biting horses

P. D. McGreevy, A. J. F. Webster and C. J. Nicol

Veterinary Record 2001 148: 592-596 doi: 10.1136/vr.148.19.592

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