Middleburg Agricultural Research and Extension Center

Background
The welfare of horses has become paramount in the equine community and the public at large, as our view of the horse has evolved from that of working livestock to a recreational companion. The MAREC research program relates to the care and welfare of the horse and to the interaction of the grazing animal and the land.

Animal welfare, evolution and environment
We view animal welfare as the good fit of an animal to its environment (Kronfeld and Parr, 1987). Evolution adapted species to their environments. Then mankind changed parts of the environment and placed extra demands on animals that were challenges to their evolved capabilities and threats to their welfare.

Directional evolution gave the modern horse a single toe, which was an advantage until the Romans built roads of lava blocks. Then the horse's foot became vulnerable to mechanical stress. Directional evolution gave the modern horse a digestive tract well suited to nibbling fibrous forages. About 300 years ago, the advent of intensive agriculture more than doubled the load of a working horse. To provide enough food energy, the hard working horse was suddenly plied with two starchy meals of grain a day. Then the horse's gut became vulnerable to digestive upsets, such as gastric ulcers and cecal distension (a form of colic) and conducive to certain metabolic disorders, for example, laminitis and certain forms of muscle disease (recurrent exterional rhabdomyolysis, RER) and skeletal disease (osteochondrosis, developmental orthopedic disease, DOD).

To improve animal welfare, genetic selection may be used to adapt the species to the environment. Alternatively, the environment may be changed to suit the animal. In the case of the horse, selection for speed and hard work has led to undesired side effects that are related positively to the desired effect in a mathematical sense, hence negatively in a phenotypic or practical sense. These side effects include bleeding (exertional pulmonary hemorrhage) and chronic infertility of mares associated with a round rump and sloping vulva.

Breeders are not selecting against speed to eliminate RER or DOD. Thus we must turn to environmental means of compensating for undesired side effects of selection for speed (and other genetic exaggerations). Moreover, caregivers are not going to cut back the horse's work-load-the twist in evolution that created the need for more feed energy. Even the promise of elucidating the genome blinks at the prospect of traits for high performance and high production, which are usually dependent upon numerous genes.

Thus the only immediate countermeasures for genetic exaggerations and blunders that bring a living horse to the brink of disorder and disease must be environmental: mechanical, the shoe; nutritional, the diet; physiological, physical conditioning; behavioral science, the handling; surgical, the stitched vulva. These categories apply equally well to ergogenic aids, which promote exercise performance. Dare we add medical and pharmacological countermeasures without risking the charge of doping? We would answer this question with prime regard for the horse's welfare.

Animal welfare and stress: a reciprocal relationship
To assess animal welfare, we have evaluated the lack of adaptation or goodness of fit to its environment as manifested in the animal as stress—emotional, adrenal and immunological, oxidative and acidogenic, alimentary and muscle.

Emotional, adrenal and immunological stress
The first well described form of stress was the general adaptation syndrome, which was recognized by Selye in the 1930s as a set of non-specific responses to any noxious stimulus. A series of responses in the lower brain, pituitary gland and adrenal cortex is central to emotional perturbation, which is also reflected in behavior.

We have conducted studies of stress in foals and mares during weaning, which combined behavioral scores and blood plasma levels of adrenal hormones (Hoffman et al., 1995; Holland et al., 1996). These studies of weaning stress have demonstrated a positive correlation between cortisol response and behavior, thus providing a valid method of welfare assessment. Since prolonged cortisol secretion affects immunity, welfare and stress may be assessed in terms of immune competence by quantifying plasma concentrations of immunoglobulins G and A.

Oxidative stress
Another general aspect of animal welfare is oxidative stress, which is an exaggeration or imbalance of a complex oxidative system in all cells. It may be manifested by certain changes in the blood.

Nearly all cells in the body are dependent on oxidation to provide energy for vital functions and to maintain their structural integrity. When unchecked, however, oxidative processes damage the DNA of genes and contribute to degenerative changes, including aging and cancer ( Harman, 1956). The rate of oxidation in muscles increases some 10- to 30-fold during a bout of strenuous exercise. The consequent oxidative stress may damage lipids in cell membranes, hence contribute to muscle damage and its preventive, fatigue (Packer, 1997). We are interested in both the immediate and accumulative effects of oxidative stress.

Oxidative stress has been suggested to contribute to several equine diseases, including the cartilage defect in DOD, the membrane damage in RER, the vascular defect in exercise-induced pulmonary hemorrhage, and degenerative motor neuron disease. It has also been implicated in the dairy cow about the time of calving. Supplementation with anti-oxidants has improved reproductive efficiency and reduced the frequency of several disorders that occur during the periparturient period. Immunity is also affected by antioxidants, such as zinc, copper, iron, selenium, vitamin A, E and C, and folate. Thus there are grounds for examining the oxidative status of horses under a variety of conditions.

Our initial studies of oxidative stress in horses undergoing endurance exercise, which were supported by the Bernice Barbour Foundation, have yielded highly encouraging results, albeit presented so far only in one abstract (Hargreaves et al., 2001). Two papers will be presented at the 6th International Conference on Equine Exercise Physiology, Lexington, KY, and three more abstracts have been submitted to the American Society of Animal Science Convention, 2002. Moreover, Dr Hoffman conducted a study of oxidative stress in polo ponies at the University of Connecticut (Hoffman et al., 2001), and she brings this experience to our group.

Acidogenic stress
Oxidation yields acid, which may be regarded as a byproduct of work. Metabolic inefficiency during work leads to stress, and stress leads to metabolic inefficiency, which generates excessive heat and acid. We have studied the effects of diet on the acidogenic effect of repeated sprints using a comprehensive physico-chemical model proposed by Peter Stewart. Most of these studies were summarized in the Animal Welfare session at the World Veterinary Congress, Yokohama, 1995 (Kronfeld et al., 1998). We now propose to study the effects of dietary energy sources on the acidogenic effect of endurance exercise.

Alimentary stress
Gastric ulcers develop commonly in horses subjected to emotional perturbation, adrenal stress and the daily feeding of large grain meals without adequate forage. Stress ('travellers') diarrhea develops commonly in association with emotional perturbation, diminished immune competence, and increased adhesion of bacteria to enterocytes. Typical is the development of salmonellosis in a hospitalized horse.

Muscle stress
During strenuous exercise causes microtrauma of muscle cells with leakage through cell membranes of proteins, such as the enzyme creatine kinase. More severe membrane damage allows myoglobin, the oxygen carrying protein, to escape, as in exertional rhabdomyolysis.

Fatigue is regarded as a safety mechanism that prevents exacerbation of microtrauma into gross structural damage of muscle or, worse, supporting structures such as tendon or bone—the dreaded 'breakdown' of the competitive equine athlete. Our studies are intended, among other objectives, to reduce the risk of breakdown through better nutrition, training and monitoring of horses engaged in hard work.

Kronfeld DS, Parr CP. 1987. Ecologic and symbiotic approaches to animal welfare, animal rights, and human responsibility. JAVMA. 191:660-664.

Hoffman RM et al. 1995. Preweaning diet and stall weaning method influence stress response of foals. J. Anim. Sci. 73: 2992-2930.

Holland JL et al. 1996. Weaning stress is affected by nutrition and weaning methods. Pferdeheilkunde 12(3): 257-260.

Harman D. 1956. A theory based on free radical and radiation chemistry. J Gerontol 11:298-300.

Packer L. 1997. Oxidants, antioxidant nutrients and the athlete. J Sports Sci. 15:353-363.

Hargreaves BJ et al. 2001. Oxidative status of endurance horses. Proc Equine Nutr Physiol Soc 17: 280-281.

Hoffman RM et al. 2001. Dietary vitamin E and ascorbic acid influence nutritional status of exercising polo ponies. Proc Equine Nutr Physiol Soc 17: 129-130.

Kronfeld DS et al. 1998. Acid-base responses of fat-adapted horses: relevance to hard work in the heat. Appl Anim Behav Sci 59: 61-72.

Currently, the feeding-fasting cycle of metabolites and hormones prompted by grain-based meals is being elucidated, because of its likely relevance to developmental orthopedic disease and other disorders associated with daily feeding of two meals rich in starch. We are now calling this cluster of abnormalities 'equine syndrome X (ESX)' by analogy with syndrome X (Kronfeld et al., 2001). 'Syndrome X' is a term proposed by Gerald Reaven (a renowned clinical endocrinologist at Stanford University) for a cluster of human abnormalities associated with chronic intakes high in starch and low in fat.

Our pasture research was recognized by the British Equine Veterinary Association in 1999 through the award of the Sir Frederick Smith Memorial Medal to David Kronfeld, who presented the memorial lecture.

Acid-base responses to exercise.
During exercise, chemical energy is converted to mechanical energy (work) and two waste products, heat and acid. Accumulation of heat and acid can make the animal uncomfortable and distressed. We have designed a complete ergogenic feed that minimizes generation of heat and acid in hard-working horses. Like the pasture supplement, it emphasizes adaptation to fat, but the fiber content is much simpler-a carefully tailored amount of slowly fermentable fiber. The latest improvement in the ergogenic feed is protein restriction (with supplementation of two limiting amino acids), which reduces the acid load all day, whereas fat adaptation reduces acid production during exercise (Graham-Thiers et al., 2001). A stress profile of nutrients also serves to sustain immunity, which is compromised by intense exercise.

Our exercise research was reviewed in the Animal Welfare session of the 1996 World Veterinary Congress in Yokohama, Japan. It was also recognized by an invitation from the Equine Nutrition and Physiology Society to present the plenary lecture on exercise at its1999 meeting.

Our pasture studies and exercise research were both cited in the presentation of the Distinguished Service Award of the Equine Nutrition and Physiology Society to David Kronfeld in 2001.

Pasture research
Much effort is being given to the development of better methods for pasture research. Markers are being tested for the measurement of fecal output, digestibility and feed intake of grazing horses. Near-infrared spectroscopy is being developed for the rapid assay of an equine profile of nutrients in pastures, with emphasis on carbohydrate fractions appropriate for horses.

The other main thrust is to apply function tests to determine optimal intakes of nutrients. Our dose response test for vitamin A status enabled the first demonstration of depletion in grazing animals (any species) during the winter. We are currently applying function tests for folate and vitamin E during the successive stages of the life cycle.

Papers cited in Recent Programs

Hoffman, R.M. et al. 2001. Hydrolyzable carbohydrates in pasture, hay and horse feeds: direct assay and seasonal variation. J Anim Sci 79: 500-506.

Kronfeld, D.S. 2001. A practical approach to feed formulation: sensitivity analysis to encompass ranges. In: Pagan J, Geor R (eds), Advances in Equine Nutrition, Volume II, Kentucky Equine Research, Versailles, KY

Kronfeld, D.S. et al. 2001. Fiber and fat feeds avoid 'equine syndrome X'. Proceedings of the American Academy of Veterinary Nutrition, Boston, MA. (Abstract)

Graham-Thiers, P.M. et al. 2001. Dietary protein restriction and fat supplementation diminish acidogenic effect of exercise during repeated sprints in horses. J Nutr 131: 1959-1964.

Bibliography, 1992-2002

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