PAPERS & ARTICLES Theriogenology 51, 1489-1503 GALLI, C., CROTTI, G., NOTARI, C., TURINI, P., DUCHI, R. & LAZZARI, G. (2001) Embryo production by ovum pick up from live donors. Theriogenology 55, 1341-1357 GIBBONS, J. R., BEAL, W. E., KRISHER, R. L., FABER, E. G., PEARSON, R. E. & GWAZDAUSKAS, F. C. (1994) Effects of once- versus twice-weekly trans- vaginal follicular aspiration on bovine oocyte recovery and embryo devel- opment. Theriogenology 42, 405-419 GIBBONS, J. R., KRISHER, R. L., CARLIN, S. K., PEARSON, R. E. & GWAZ- DAUSKAS, F. C. (1995) In vitro embryo production after microinjection and ovarian dynamics following transvaginal follicular oocyte aspiration. Theriogenology 43, 1129-1139 HALL, L. W. & CLARKE, K. W. (1991) Anaesthesia of the ox. In Veterinary Anaesthesia. 9th edn. London, W. B. Saunders. pp 236-259 KRUIP, T. A., PIETERSE, M. C., VAN BENEDEN, T. H., VOS, P. L., WURTH, Y. A. & TAVERNE, M. A. (1991) A new method for bovine embryo produc- tion: a potential alternative to superovulation. VeterinaryRecord 128,208-210 PETYIM, S., BAGE, R., FORSBERG, M., RODRIGUEZ-MARTINEZ, H. & LARSSON, B. (2000) The effect of repeated follicular puncture on ovarian function in dairy heifers. Journal of Veterinary Medicine A 47, 627-640 PETYIM, S., BAGE, R., FORSBERG, M., RODRIGUEZ-MARTINEZ, H. & LARSSON, B. (2001) Effects of repeated follicular punctures on ovarian morphology and endocrine parameters in dairy heifers. Journal ofVeterinary Medicine A 48, 449-463 PIETERSE, M. C., KAPPEN, K. A., KRUIP, T. A. M. & TAVERNE, M. A. M. (1988) Aspiration of bovine oocytes during transvaginal ultrasound scan- ning of the ovaries. Theriogenology 30, 751-762 PIETERSE, M. C., VOS, P. L. A. M., KRUIP, T. A. M., WILLEMSE, A. H. & TAVERNE, M. A. M. (1991a) Characteristics of bovine estrous cycles during repeated transvaginal, ultrasound-guided puncturing of follicles for ovum pick-up. Theriogenology 35, 401-413 PIETERSE, M. C., VOS, P. L. A. M., KRUIP, T. A. M., WURTH, Y. A., VAN BENEDEN, T. H., WILLEMSE, A. H. & TAVERNE, M. A. M. (1991b) Transvaginal, ultrasound guided follicular aspiration of bovine oocytes. Theriogenology 35, 857-862 REIS, A., STAINES, M. E., MCCALLUM, G. C., WATT, R. G., DOLMAN, D. F. & MCEVOY, T. G. (2000) Bovine blastocyst yields following zygote culture in defined medium depend on the source of selected oocytes. In Early Regulation of Mammalian Development. British Society of Animal Science International Symposium. September 18 to 20, 2000. Aberdeen, UK. p 22 ROCHA, A., BROUSSARD, J., BLAIR, R. M., LIM,J. M., MEINTJES, M., ROUS- SEL, J. D., GODKE, R. A. & HANSEL, W. (1996) Effect of unilateral ovari- ectomy, gonadotropin stimulation and immunization against a synthetic peptide of the inhibin a-subunit on follicular development and oocyte recov- ery in cattle. Theriogenology 46,605-616 SANTL, B., WENIGERKIND, H., SCHERNTHANER, W., MODL, J., STOJ- KOVIC, M., PRELLE, K., HOLTZ, W., BREM, G. & WOLF, E. (1998) Comparison of ultrasound-guided vs laparoscopic transvaginal ovum pick- up (OPu) in Simmental heifers. Theriogenology 50,89-100 SCOTT, C. A., ROBERTSON, L., DE MOURA, R. T. D., PATERSON, C. & BOYD, J. S. (1994) Technical aspects of transvaginal ultrasound-guided fol- licular aspiration in cows. Veterinary Record 134, 440-443 SHAW, D. W. & GOOD, T. E. (2000) Recovery rates and embryo quality following dominant follicle ablation in superovulated cattle. Theriogenology 53, 1521-1528 SNEL-OLIVEIRA, M. V., TURY, E., PEREIRA, D. C., MALAGOLI, D. Jr,. NASCIMENTO, N. V., SANTOS, E. S. & RUMPF, R. (2002) Histopathological lesions in the ovaries after ultrasound guided transvaginal ovum pick up (OPU) in Nelore prepubertal calves. Theriogenology 57, 687- STUBBINGS, R. B. & WALTON, J. S. (1995) Effect of ultrasonically-guided follicle aspiration on estrous cycle and follicular dynamics in Holstein cows. Theriogenology 43, 705-712 VIGORITA, V. J. & GHELMAN, B. (1999) Arthritis. In Orthopaedic Pathology. 1st edn. Philadelphia, Lippincott Williams & WiLkins. pp 570-620 Study of crib-biting and gastric inflammation and ulceration in young horses C. J. NIcoL, H. P. D. DAVIDSON, P. A. HARRIS, A. J. WATERS, A. D. WILSON Nineteen young horses that had recently started to perform the stereotypy of crib-biting were compared with 16 non-stereotypic horses for 14 weeks. After initial observations of their behaviour and an endoscopic examination of the condition of their stomachs, the horses were randomly allocated to a control or an antacid diet. At the start of the trial, the stomachs of the crib-biting foals were significantly more ulcerated and inflamed than the stomachs of the normal foals. In addition, the faecal pH of the crib-biting foals (6-05) was significantly lower than that of the normal foals (6-58). The antacid diet resulted in a significant improvement in the condition of the horses' stomachs. The crib-biting behaviour declined in most of the foals, regardless of their diet, but tended to decline to a greater extent in the foals on the antacid diet. STEREOTYPIES are repetitive behaviours which become increasingly fixed in form and orientation (Mason 1991). Dietary factors have been strongly associated with the devel- opment of oral stereotypies (Rushen and others 1993) but plausible mechanisms linking a feeding practice to the devel- opment of a stereotypy have rarely been proposed, let alone investigated. Crib-biting is an oral stereotypy performed by approxi- mately 5 per cent of captive domestic horses (McGreevy and others 1995a, Redbo and others 1998, Nicol 1999); a fixed object is grasped with the incisor teeth, the lower neck mus- cles contract to retract the larynx caudally, and air is drawn into the cranial oesophagus, producing a characteristic grunt. Air is not swallowed (McGreevy and others 1995b) but there is a view that crib-biting is harmful, and restrictive devices and/or surgery are widely employed to stop the behaviour, with limited success and against the best interests of the indi- vidual horse (McGreevy and Nicol 1998). Texts from the 19th century to the present day state that crib-biting is caused by idleness or boredom (Wortley Axe 1905, Codrington 1974). In contrast, recent epidemiological work has shown that the risk of crib-biting is increased by a low forage or high grain diet (McGreevy and others 1995a, Waters and others 2002). Although the mechanism(s) governing this effect are not known, it has been proposed that horses may begin crib-bit- ing to increase their flow of alkaline saliva (Nicol 1999). Saliva is essential to buffer gastric acidity in horses, but it is secreted only during mastication (Alexander and Hickson 1970). Horses fed low forage or high grain diets may produce insuf- ficient saliva to buffer their stomach contents, and may seek Veterinary Record (2002) 151, 658-662 C. J. Nicol, MA, DPhil, A. J. Waters, BSc, PhD, A. D. Wilson, PhD, MRCVS, Department of Clinical Veterinary Science, University of Bristol, Langford House, Bristol BS40 5DU H. P. D. Davidson, BSc, P. A. Harris, PhD, MRCVS, Equine Studies Group, Waltham Centre for Pet Nutrition, Leicestershire LE14 4RT The Veterinary Record, November 30, 2002 658