Effect of feed deprivation on daily water consumption in healthy horses

Measurements of water consumed by fed healthy horses might not apply to horses that are unwilling or unable to drink or are not fed for any reason.

To examine the effects of feed deprivation on voluntary water consumption compared with fed conditions.

In vivo experiment.

Eight healthy adult Thoroughbred geldings were used in a randomised crossover design so that each horse served as its own control for fed vs feed-deprived conditions. Water intake, bodyweight, physical findings and vital signs were measured during 4 days of feeding and 4 days of feed deprivation. Daily measurements during the trial periods were PCV, TPP, electrolytes, osmolality and triglycerides. Plasma and extracellular fluid volumes were measured in the last 8 hours of the trial periods. Data were analysed with a two-way analysis of variance with repeated measures, and statistical significance was P ≤ .05.

Feed deprivation immediately and persistently reduced water consumption to ~16% of fed values, with laboratory evidence of mild dehydration on day 4.

Changes in total body water and in water and electrolyte excretion or conservation through faeces and urine were not measured.

Feed consumption has a marked effect on water requirements in healthy horses. Because current guidelines for water needs were obtained in the fed state, they might not apply to horses that are denied feed for any reason or have reduced feed intake. This study provides new information on water consumption in horses that should apply to this essential nutrient in health and disease.