Withholding Feed Affects Water Intake in Horses

Horses sometimes refuse to drink following competition. One study shows that decreased water intake may result from decreased feed consumption.^*

Horses primarily drink water after eating. This behavior appears to be prompted by the large volumes of water that move into the large colon after a meal, drawing it out of circulation. As a result, horses feel dehydrated, essentially spiking thirst and driving them to drink.

“Owners withhold feed from their horses for a variety of reasons: before transport, prior to competition, or even by feeding ‘meals’ twice a day rather than allowing horses more continual access to feed,” advised Catherine Whitehouse, M.S., a Kentucky Equine Research nutrition advisor.

Feeding patterns and behaviors could therefore have a profound effect on a horse’s water intake and overall hydration status, performance, and health.

To better understand patterns of voluntary water intake, the amount of water consumed by eight fed and fasted horses was measured for four days. When fed, horses were offered high-grain diets consisting of 4.5 lb (2 kg) grain and 18 lb (8 kg) Bermudagrass hay per day divided into two meals. All horses had access to 40 liters of fresh water throughout the study period. Various physical and laboratory data were collected and analyzed during the study.

Key findings included:

• Feed deprivation did not cause any changes in vital signs or physical examination findings;
• Horses remained alert and responsive to their environments. They did not have any behavior changes, such as eating bedding or splashing in the water;
• Assessment of mucous membranes revealed no indication of dehydration;
• Horses lost 7.2% of their body weight during the four-day study period;
• Voluntary water intake was significantly lower when feed was deprived;
• The decrease in water intake began within 12 hours of withholding feed;
• Fecal and urine output appeared to decline based on direct observation;
• Sodium was significantly reduced during the feed deprivation; and
• Although still within normal limits, blood urea nitrogen and creatinine levels were significantly higher in feed-deprived horses, consistent with mild dehydration.

“Feed deprivation resulted in an immediate and consistent reduction in voluntary water consumption. Horses appeared to only become mildly dehydrated, likely because horses can draw water from their large colon to preserve water balance for a short period of time,” explained Whitehouse.

In sum, these results confirm that even short-term withdrawal of feed results in a substantial decrease in voluntary water consumption. Therefore, feed interruptions for horses being transported for competition, for example, can potentially negatively affect performance due to inadequate hydration levels.

“Horses with decreased feed consumption, either due to reduced appetite or management strategies, may be at risk for chronic mild or low-grade dehydration. This may be particularly salient for horses actively involved in competition. An electrolyte supplement offered with water in conjunction with a small meal may help tempt voluntary water intake,” advised Whitehouse.

*Freeman, D.E., A. Mooney, S. Giguère, J. Claire, C. Evetts, and P. Diskant. 2021. Effect of feed deprivation on daily water consumption in healthy horses. Equine Veterinary Journal 53(1):117-124.