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Houpt, K. A. (1990). Ingestive behavior. Vet Clin North Am Equine Pract, 6(2), 319–337.
Abstract: In summary, horses spend 60% or more of their time eating when grazing or when feed is available free choice. Grasses are their preferred food, but they supplement the grass with herbs and woody plants. Sweetened mixtures of oats and corn are the most preferred concentrate. Horses can increase or decrease the time spent eating and amount eaten to maintain caloric intake. Their intake is stimulated by drugs such as diazepam and by the presence of other horses. Horses stop eating when gastric osmolality increases; increases in plasma osmolality, protein, and glucose accompany digestion. Foals eat several times an hour and begin sampling solid food at the same time that their dam is eating. Several areas of particular importance to the equine industry have not been investigated. These areas include the effect of exercise on short- and long-term food intake and the influence of reproductive state on the feeding of mares.
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Houpt, K. A. (1991). Animal behavior and animal welfare. J Am Vet Med Assoc, 198(8), 1355–1360.
Abstract: The value of behavioral techniques in assessing animal welfare, and in particular assessing the psychological well being of animals, is reviewed. Using cats and horses as examples, 3 behavioral methods are presented: (1) comparison of behavior patterns and time budgets; (2) choice tests; and (3) operant conditioning. The behaviors of intact and declawed cats were compared in order to determine if declawing led to behavioral problems or to a change in personality. Apparently it did not. The behavior of free ranging horses was compared with that of stabled horses. Using two-choice preference tests, the preference of horses for visual contact with other horses and the preference for bedding were determined. Horses show no significant preference for locations from which they can make visual contact with other horses, but they do prefer bedding, especially when lying down. Horses will perform an operant response in order to obtain light in a darkened barn or heat in an outside shed. These same techniques can be used to answer a variety of questions about an animal's motivation for a particular attribute of its environment.
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Houpt, K. A. (1995). New perspectives on equine stereotypic behaviour (Vol. 27).
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Houpt, K. A. (2006). Why horse behaviour is important to the equine clinician. Equine Vet J, 38(5), 386–387.
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Houpt, K. A., & Feldman, J. (1993). Animal behavior case of the month. Aggression toward a neonatal foal by its dam. J Am Vet Med Assoc, 203(9), 1279–1280.
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Houpt, K. A., & Smith, R. (1993). Animal behavior case of the month. J Am Vet Med Assoc, 203(3), 377–378.
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Houpt, K. A., & Wolski, T. R. (1980). Stability of equine hierarchies and the prevention of dominance related aggression. Equine Vet J, 12(1), 15–18.
Abstract: The dominance hierarchy of a herd of 10 Thoroughbred mares was determined twice, at an interval of 18 months, using paired feeding tests. Each mare's rank was correlated significantly between the 2 tests. This indicated that the hierarchy within the herd was stable. The offspring of dominant and subordinate mares were also tested for dominance in their own age groups. The offspring of dominant mares tended to be near the top of the hierarchy while those of middle and low ranking mares were not consistently found in the middle or bottom of their own hierarchies. Paired feeding tests were carried out on 8 ponies. During tests the time that each pony spent eating and the ponies' aggressive interactions were recorded. Two situations were used. Each pony-pair was tested when both ponies were in the same paddock and also when they were separated by a rail fence. The subordinate ponies spent significantly more time eating and the domonant pony was significantly less aggressive, when the pony-pair was separated by a fence than when they were in one paddock. It was concluded that the dominance hierarchies of adult horse groups changed very little over time and that the foals of dominant mares will tend to be dominant in their own age groups. Management practices can be used to reduce aggression and consequent injury that may arise in group feeding situations.
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Houpt, K. A., Eggleston, A., Kunkle, K., & Houpt, T. R. (2000). Effect of water restriction on equine behaviour and physiology. Equine Vet J, 32(4), 341–344.
Abstract: Six pregnant mares were used to determine what level of water restriction causes physiological and/or behavioural changes indicative of stress. Nonlegume hay was fed ad libitum. During the first week of restriction, 5 l water/100 kg bwt was available, during the second week 4 l/100 kg bwt and, during the third week, 3 l/100 kg bwt. Ad libitum water intake was 6.9 l/100 kg bwt; at 3 l/100 kg bwt water intake was 42% of this. Daily hay intake fell significantly with increasing water restriction from 12.9 +/- 0.75 kg to 8.3 +/- 0.54 kg; bodyweight fell significantly for a total loss of 48.5 +/- 8.3 kg in 3 weeks. Daily blood samples were analysed; osmolality rose significantly with increasing water restriction from 282 +/- 0.7 mosmols/kg to 293.3 +/- 0.8 mosmols/kg bwt, but plasma protein and PCV did not change significantly. Cortisol concentrations fell from 8.1 ng/ml to 6.4 ng/ml over the 3 week period. Aldosterone fell from 211.3 +/- 74.2 pg/ml to 92.5 +/- 27.5 pg/ml at the end of the first week. The behaviour of 4 of the 6 mares was recorded 24 h/day for the duration of the study. The only significant difference was in time spent eating, which decreased with increasing water restriction from 46 +/- 3% to 30 +/- 3%. It is concluded that water restriction to 4 l/100 kg bwt dehydrates pregnant mares and may diminish their welfare, but is not life- or pregnancy-threatening.
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Houpt, K. A., Perry, P. J., Hintz, H. F., & Houpt, T. R. (1988). Effect of meal frequency on fluid balance and behavior of ponies. Physiol. Behav., 42(5), 401–407.
Abstract: Twelve ponies were fed their total daily ration either as one large meal or divided into six small meals. Pre- and post-feeding behavior was recorded six times a day. Blood samples were taken for 30 min before and two hr after the meal. Plasma protein increased from 7.0 to a peak of 7.3 g/dl with small meals and from 7.3 to 8.1 g/dl with large meals, and returned to pre-feeding levels by 90 min post-feeding. Hematocrit rose from 33.3 to 34.1% with small meals and from 33.0 to 36.0% with large meals. These rapid and short-lived increases indicate a decrease in plasma volume. Plasma osmolality rose with feeding from 283 to 285 mosmoles/kg with small meals and from 281 to 288 mosmoles/kg with large meals. Water availability had no significant effect on blood changes. Digestibility and rate of passage were measured with chromic oxide, but there were no differences. Vocalizing (neighing) and walking occurred more often before than after feeding, while eating bedding and engaging in other oral behaviors were more frequent after feeding.
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Houpt, K. A., Thornton, S. N., & Allen, W. R. (1989). Vasopressin in dehydrated and rehydrated ponies. Physiol. Behav., 45(3), 659–661.
Abstract: Six pony mares deprived of water for 24 hours showed significant increases in plasma vasopressin (2.8 pg/ml) and osmolality (9 mosmol/kg). When water was made available the ponies drank rapidly (5 of 6 drank to satiety within 90 seconds) and corrected their fluid deficits precisely. Vasopressin did not return to predehydration levels until osmolality did after 15 minutes of access to water. The horse differs from rodents and humans, but is similar to pigs in that vasopressin levels do not fall before osmolality returns to normal. Oropharyngeal factors, therefore, may not be as important in vasopressin release in horses as in other species.
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