Effect of water restriction on equine behaviour and physiology.

The study investigates the effects of water restriction on pregnant horses. It finds that limiting water intake causes physiological and behavioral changes associated with stress.

Research Methodology

• The study utilized six pregnant mares to investigate the level of water restriction that brings about physiological and/or behavioral changes suggestive of stress.
• Each mare was fed nonlegume hayad libitum(a diet provided freely and unrestricted) throughout the experiment.
• The investigators systematically decreased the water intake of the mares over three weeks – 5 liters per 100 kg body weight (bwt) in the first week, 4 liters per 100 kg bwt in the second week, and 3 liters per 100 kg bwt in the final week. The average ad libitum water intake was 6.9 liters per 100 kg bwt, which means the most severe water restriction (3 liters per 100 kg bwt) only provided 42% of the typical ad libitum water intake.

Results

• The results revealed a significant decrease in daily hay intake with increasing water restriction, falling from 12.9 +/- 0.75 kg to 8.3 +/- 0.54 kg. The bodyweight of the mares also significantly decreased, resulting in a total weight loss of 48.5 +/- 8.3 kg over the three weeks.
• The study demonstrated physiological changes. The osmolality, a measure of concentration in bodily fluids, significantly increased with water restriction, going from 282 +/- 0.7 mosmols/kg to 293.3 +/- 0.8 mosmols/kg bwt. However, plasma protein and packed cell volume (PCV), two key blood parameters, didn’t show significant changes.
• Two stress hormone levels – cortisol and aldosterone – were monitored throughout the experiment. Both hormones significantly decreased; cortisol fell from 8.1 ng/ml to 6.4 ng/ml, while aldosterone fell from 211.3 +/- 74.2 pg/ml to 92.5 +/- 27.5 pg/ml. This decline indicates the animals were stressed.
• From a behavioural perspective, the study found the only significant difference was in the time the animals spent eating. This activity decreased with increasing water restriction – dropping from 46 +/- 3% to 30 +/- 3%.

Conclusion

• The investigation concludes that restricting water intake to 4 liters per 100 kg bwt dehydrates pregnant mares and may affect their welfare negatively. Though the imposed water restriction is not life-threatening or leading to miscarriages, it does cause stress and discomfort to the animals.