Effect of water restriction on equine behaviour and physiology.
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.
Houpt
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Department of Physiology, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853-6401, USA.
Eggleston
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Kunkle
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Houpt
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D000818:Animals; D001522:Behavior, Animal; D001798:Blood Proteins / Q000032:analysis; D002149:Energy Intake; D005260:Female; D006734:Horse Diseases / Q000503:physiopathology; D006736:Horses / Q000502:physiology*; D009994:Osmolar Concentration; D011247:Pregnancy; D013312:Stress, Physiological / Q000662:veterinary; D014741:Video Recording; D014868:Water Deprivation / Q000502:physiology*
D001798:Blood Proteins