Effect of water restriction on equine behaviour and physiology

Sis pregnant mares were used to determine what level of water restriction c auses physiological and/or behavioural changes indicative of stress. Nonleg ume hay was fed ad libitum. During the first week of restriction, 5 l water /100 kg bwt was available, during the second meek 4 l/100 kg bmt and, durin g the third week, 3 l/100 kg bmt. 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 +/- 0.53 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 incre asing water restriction from 282 +/- 0.7 mosmols/kg to 293.3 +/- 0.8 mosmol s/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. Al dosterone fell from 211.3 +/- 74.2 pg/ml to 92.5 +/- 27.5 pg/ml at the end of the first meek. 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.