Abstract: There is confusion in the veterinary literature concerning the definition of oral based stereotypies in the horse. This study reports the use of fluoroscopy and endoscopy during cribbiting/wind-sucking in afflicted horses. This permitted observations of movements of the pharyngeal and oesophageal tissues and of the air column within during the stereotypic behaviour. The findings reported show that the sequence of events during crib-biting/wind-sucking is not related to deglutition and that air is not swallowed to the stomach. Transient dilation of the upper oesophagus was recorded and the characteristic noise of wind-sucking coincided with the in-rush of air through the cricopharynx. The oesophageal distension was relieved when the air returned to the pharynx although small quantities passed caudally. It is proposed that the role of contraction of the strap muscles of the neck is to create a pressure gradient in the soft tissues surrounding the oesophagus which provokes movement of air from the pharynx into the oesophagus. The findings suggest that the definitions currently used in the sale of horses are in need of revision.

Abstract: Fourteen riding horses of mixed age and breed were randomly allocated to observer and control treatments. An additional horse was pre-trained as a demonstrator to walk the 13.8 m length of the test arena and select one of two food buckets using colour and pattern cues. Observer horses were exposed to correct performances of the task by the trained demonstrator, for 20 trials held over 2 days. Control horses were subjected to the same handling and placement procedures as the observer horses but without exposure to the behaviour of the demonstrator. The third day for all subjects was designated as a test day. Each subject was released individually in a predetermined place in the arena, and the latency to walk the length of the test arena to the food buckets, the latency to feed, the identity of the bucket approached and the identity of the bucket selected were recorded on ten consecutive trials. During tests both food buckets contained food to minimize the possibility of individual trial and error learning. On the first trial the mean latency to approach the goal area was 18 s for observer horses, compared with 119 s for control horses (t = 2.8, d.f. = 12, P < 0.01) and the mean latency to eat was 35 s for observer horses, compared with 181 s for control horses (t = 4.86, d.f. = 11, P < 0.001). However, observer horses were no more likely to choose the demonstrated bucket than control horses on the first trial. Twelve of the 14 horses decreased their latency to approach the goal area during the series of ten trials, but there were no significant changes in the buckets selected.

Abstract: Developmental pathologies may result from endogenous or xenobiotic-enhanced formation of reactive oxygen species (ROS), which oxidatively damage cellular macromolecules and/or alter signal transduction. This minireview focuses upon several model drugs (phenytoin, thalidomide, methamphetamine), environmental chemicals (benzo[a]pyrene) and gamma irradiation to examine this hypothesis in vivo and in embryo culture using mouse, rat and rabbit models. Embryonic prostaglandin H synthases (PHSs) and lipoxygenases bioactivate xenobiotics to free radical intermediates that initiate ROS formation, resulting in oxidation of proteins, lipids and DNA. Oxidative DNA damage and embryopathies are reduced in PHS knockout mice, and in mice treated with PHS inhibitors, antioxidative enzymes, antioxidants and free radical trapping agents. Thalidomide causes embryonic DNA oxidation in susceptible (rabbit) but not resistant (mouse) species. Embryopathies are increased in mutant mice deficient in the antioxidative enzyme glucose-6-phosphate dehydrogenase (G6PD), or by glutathione (GSH) depletion, or inhibition of GSH peroxidase or GSH reductase. Inducible nitric oxide synthase knockout mice are partially protected. Inhibition of Ras or NF-kB pathways reduces embryopathies, implicating ROS-mediated signal transduction. Atm and p53 knockout mice deficient in DNA damage response/repair are more susceptible to xenobiotic or radiation embryopathies, suggesting a teratological role for DNA damage, consistent with enhanced susceptibility to methamphetamine in ogg1 knockout mice with deficient repair of oxidative DNA damage. Even endogenous embryonic oxidative stress carries a risk, since untreated G6PD- or ATM-deficient mice have increased embryopathies. Thus, embryonic processes regulating the balance of ROS formation, oxidative DNA damage and repair, and ROS-mediated signal transduction may be important determinants of teratological risk.

Abstract: Social influences on established behaviour and on the acquisition of new information and behaviour are reviewed. Distinctions between social facilitation and contagious behaviour are drawn and suggestions for further research on contagious behaviour are made. Socially derived visual, olfactory and auditory cues are considered as important influences on behaviour and subsequent learning. The evidence supporting two potential mechanisms of social learning, i.e. stimulus enhancement followed by individual learning, and imitation, is reviewed in detail. It is argued that the functions of social learning are similarly heterogeneous and include motor skill acquisition, gathering of environmental information, and social conformity. Factors affecting the spread of socially acquired skills, including the social relationship between demonstrator and observer, are highlighted. Lastly, the few studies of social learning that have been conducted with domestic species are reviewed and potential applied goals that could stimulate further research in this area are suggested.

Abstract: Crib-biting is a common oral stereotype. Because of perceived deleterious effects on the health and appearance of subjects the prevention of crib-biting is regularly attempted. The resourcefulness of horses in satisfying their motivation to perform this behaviour often frustrates owners' efforts at prevention. This paper reviews the efficacy and observable consequences of attempting to prevent crib-biting by a variety of methods. These include attempts to prevent the grasping of objects, to interfere with air-engulfing and to introduce punishment for grasping and neck-flexion. Other approaches include the use of surgery, acupuncture, pharmaceuticals, operant feeding and environmental enrichment. A remedy that is effective for every crib-biter remains elusive. We conclude that, rather than concentrating on remedial prevention, further research should be directed at establishing why horses crib-bite and how the emergence of crib-biting can be avoided.