urine | Horse Racing Free Tips

Study: 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 pounds (2 kg) grain and 18 pounds (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 percent 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.

New Test Can Detect Bisphosphonate Three Years After Administration

A new study may give regulators the key to better regulate bisphosphonate use in racing. Controversy has surrounded bisphosphonate use since the drug became approved by the Food and Drug Administration (FDA) for use in horses. Bisphosphonates are labeled for adult horses battling navicular syndrome and similar chronic conditions that don't respond to other types of treatment.

The FDA has licensed two bisphosphonates, which are sold under the trade names Tildren and Osphos. The Horse reports that there are other, non-licensed versions of bisphosphonates marketed for horses which are not FDA-approved. Those non-approved products are advertised as being more powerful than the two approved versions.

The FDA prohibits the use of bisphosphonates in horses younger than four years old, but some owners and trainers continue to use the product off-label on young horses. Bisphosphonates impact the build-up/breakdown cycle in bone, which veterinarians say could have negative effects on growing animals.

Dr. Christopher Riggs, chief advisor in veterinary science at The Hong Kong Jockey Club, studied 24 Thoroughbreds who had received a single therapeutic dose of tiludronate disodium between one month to three years earlier. The research team then tested blood plasma and urine samples using ultra‐high‐performance liquid chromatography high‐resolution mass spectrometry, a new testing technology. The tests found traces of tiludronate disodium in every sample.

Previously, testing was only able to detect bisphosphonates in equine blood or urine if it had been administered in the last 40 days. Hair testing could detect an administration from months prior, but is limited in its ability to pinpoint the time of administration.

Researchers believe the drug lingers on the surface of bone, occasionally releasing back into the horse's body for months or years, but little is known about how long that effect could go on. The drug may be more detectable in horses that are going through training and rest periods that affect bone remodeling.

Excessive Drinking May Indicate Ill Health

Horses that urinate excessively suffer from polyuria (PU); to remain adequately hydrated, the horse must increase his drinking, called polydipsia (PD). These conditions, which often go hand-in-hand, can indicate disease or a behavior problem, or be a consequence of diet, says Dr. Harold Schott of Michigan State University.

A horse's kidneys filter waste products from the blood and eliminate them from the body in the form of urine. They also regulate the volume of water in the body by concentrating or diluting urine. Nearly 100 percent of water filtered from the blood is reabsorbed by the kidney tubules. A small decrease in water reabsorption can result in a large increase in urine production.

Diet affects urine output in distinct ways. A foal drinking his dam's milk may ingest as much as five times as much water as an adult horse and produce clear urine 10 to 12 times a day. A mature horse on an all-hay diet may only pass dark yellow urine two or three times a day. Horses fed mainly alfalfa may have wetter stalls with fewer manure piles; this is because legume hay is higher in protein and calcium, and is more digestible than grass hay.

Excessive urination can be caused by chronic kidney disease (CKD), where the kidneys can no longer produce concentrated urine. A horse suspected of having this disease will need blood drawn to test its nitrogen and creatinine concentrations, which will be higher if the horse has CKD.

If urine samples collected from the affected horse show nothing out of the ordinary, the horse may be drinking excessive amounts of water out of boredom. This occurs most often in horses that are confined to stalls most of the day. This behavior can be modified by allowing the horse more turnout time or limiting his water supply to two five-gallon buckets a day.