Tag: Horse Care

When it comes to consumption of spring pasture, horses and ponies hardly hold back; horses can consume over 3 percent and ponies up to 5 percent of body weight daily. “Given that horses and ponies usually consume 1.5 to 2 percent of their body weight in forage and feed to maintain body weight, these numbers alone explain why horse owners run into problems with lush grass,” said Kathleen Crandell, Ph.D., a nutritionist with Kentucky Equine Research.

Despite its nutritional benefits, spring grass can be high in sugar and starch, depending on the type of grass. “Levels of nonstructural carbohydrates (NSC) as high as 40 percent dry matter have been recorded in certain grasses. Cool season perennials—like ryegrass, timothy, orchardgrass, bluegrass—are especially predisposed to accumulating sugars and fructans,” explained Crandell.

Let's review some of the common issues that can spring up along with green grass.

Colic. Access to pasture is generally associated with a decreased risk of colic. When it comes to spring grass, though, colic risk rises, primarily due to changes that occur in the gastrointestinal environment consequent to overconsumption.

Issues arise because the high carbohydrate content of lush grass may cause rapid fermentation of fiber in the hindgut, upsetting the microbial balance and causing excessive gas production. With any shift in the microbial population of the digestive tract, an increase in gas-producing microbes can occur. The microbes that ferment sugars and fructans produce copious amounts of gas. “If there is good flow to the digesta in the tract, which is often the case with high-moisture spring grass, the gas will be easily expelled, although it may cause mild discomfort,” Crandell said.

She added, “Horses that are on pasture 24/7 during the winter and into the spring as the grass begins to green up have fewer problems than those who are suddenly introduced to grass because the intestinal microbiome has time to adapt to the changes gradually.”

Further, certain horses may have a problem transitioning from a high-fiber diet of hay or mature grass to lush grass, which has a much lower fiber content. Lack of fiber may cause intestinal upset. This is one reason why many owners offer hay to horses at the same time they're consuming lush pasture grasses.

Laminitis. Several modes of action may cause laminitis depending on the individual horse and its susceptibility.

One chain of events involves the hindgut. When a horse consumes spring grass, some of the sugar in it bypasses digestion in the small intestine and ends up in the hindgut. This produces a bloom of lactate-producing gram-negative bacteria that rapidly ferments the sugar and fructans. The byproduct of this fermentation is increasing amounts of lactic acid, which drop the pH of the hindgut. As the pH decreases, other microbes die, releasing endotoxins, reactive amines, and exotoxins into the bloodstream. These are thought to adversely affect circulation, increase inflammation, and destroy lamellar basement membranes in the hooves, causing laminitis.

Another mode of action implicates insulin dysregulation. Consumption of high-sugar grasses causes a rise in blood glucose, which triggers a release of insulin in an attempt to reduce glucose levels by helping to usher it into cells. If a horse or pony is insulin resistant, this mechanism malfunctions, so the pancreas releases more insulin, gradually increasing levels of insulin in the bloodstream. This hyperinsulinemia triggers alterations in blood flow to the hoof, boosts expression of lamellar pro-inflammatory cytokines that activate inflammation, and alters glucose metabolism within the hoof lamellae.

Loose manure. A change in manure is common when horses consume lush spring grass, most likely because of the elevated water content of grasses, which can reach 85 percent. If the horse's manure has green-cowpie consistency when first allowed to graze in the springtime, then the cause is probably the new diet, not disease, Crandell said.

However, horses can develop pathological diarrhea, particularly if they are allowed full-on access to spring grass without acclimation. A dramatic shift in the makeup of the hindgut microbiome, as described previously, can make the horse more susceptible to blooms of pathogenic bacteria that naturally reside in the hindgut. Always consult with a veterinarian when drastic changes occur in a horse's manure, especially if it is watery and lasts more than a day or two.

Wood-chewing. Horses require fiber in their diets. Because springtime grass contains little fiber, some horses will look elsewhere to satisfy this need. Horses often chew fence boards or rip bark from trees as a way to consume more fiber. Horses may colic from eating indigestible wood, possibly as a result of impaction.

Safe springtime turnout requires planning. According to Crandell, management strategies include:

• Gradually acclimating horses unaccustomed to spring pasture by allowing more and more turnout per day and feeding hay the remainder of the day. Start with 20-30 minutes of exposure on the first day of grazing and then increase by 30 minutes every one to two days. Again, this would not be necessary if the horse has access to the pasture throughout the entire transition from winter to spring.
• Using a grazing muzzle to slow the consumption of the fresh grass.
• Continuing to offer hay to horses on pasture to give them more fiber. A flake or two is usually enough to discourage wood-chewing.
• Feeding a research-proven hindgut buffer like EquiShure two to three times a day throughout springtime. EquiShure keeps the pH of the hindgut steady, decreasing the likelihood of sweeping shifts in the microbial population.

Reprinted courtesy of Kentucky Equine Research. Visit ker.com for the latest in equine nutrition and management, and subscribe to Equinews to receive these articles directly.

“Experts suggest that stereotypic behaviors develop in horses secondary to stress-related events such as stall confinement, isolation from herdmates or poor herd dynamics, training, and feeding programs,” explained Catherine Whitehouse, M.S., a nutritionist for Kentucky Equine Research. “The incidence or development of stereotypic behaviors generally increases when forage intakes are low and can be exacerbated by feeding large amounts of concentrates.”

Once horses begin displaying stereotypic behaviors, treatment options are extremely limited. Reports suggest that fluoxetine effectively reduces the occurrence of stereotypic behaviors. A study on fluoxetine metabolism, however, shows that fluoxetine behaves differently in horses than in humans.

Fluoxetine is classified as a selective serotonin reuptake inhibitor (SSRI). This type of medication allows the neurotransmitter serotonin to persist in the brain for longer periods of time. In humans, doctors prescribe fluoxetine for a variety of conditions related to anxiety and depression.

Studies show that trazodone, another well-known SSRI, reduces a variety of stereotypical behaviors in horses but causes excitation, aggression, muscle fasciculations, and incoordination. Fluoxetine, on the other hand, appears effective in horses for improving stereotypic behaviors without the side effects noted with trazodone.

These anecdotal reports suggest that horses respond to human doses of fluoxetine, about 125 mg for an average 1,100-pound horse. Despite these anecdotal reviews, veterinarian researchers recently pointed out that without any studies on fluoxetine absorption, metabolism, or elimination, no accurate information exists on appropriate dosing, safety, or effectiveness.

Rather than relying on anecdotal reports for dosing information, the research team recruited healthy, client-owned horses without stereotypical behaviors. In the first part of the study, those horses were administered a compounded fluoxetine paste. Each horse received a single dose of fluoxetine paste (equivalent to 0.25 mg/kg) after being fasted overnight. Blood samples were collected prior to administration, intermittently throughout the first day, and again at two days and seven days following administration.

In the second part of this study, horses were administered fluoxetine (0.25 mg/kg) by mouth once daily for eight weeks.

This study revealed that fluoxetine was more rapidly absorbed and eliminated in horses than in other species; however, once-daily dosing maintained steady circulating drug levels. Because healthy horses were used, the therapeutic efficacy of this dose (0.25 mg/kg) could not be established based on this study. That said, no adverse effects were observed in this population of horses.

“One particularly interesting finding was that the fluoxetine metabolite norfluoxetine was not detectable in horses. In humans, fluoxetine is metabolized to norfluoxetine and both compounds have therapeutic effects,” said Whitehouse. “The fact that no norfluoxetine was found in horses further shows that drug absorption and metabolism differ markedly in horses than other species. As a result, limited recommendations can be made on fluoxetine use in horses based on data obtained in other species.”

Recently, many research groups in human and veterinary medicine report that neurotransmitter levels in the brain, including serotonin, can be modulated via the “gut-brain-microbiome axis.” While the exact mechanisms are not known, preliminary data show that modulating brain neurotransmitters by gut microbiota plays a key role in the pathophysiology of anxiety and depression. As such, manipulating the gut microbiota could provide a novel way to alter neurotransmitter levels in the brain to treat anxiety and depression.

“Episodes of stress can negatively affect digestive health and the development of stereotypic behaviors. Eliminating all potential stressors is not possible, but owners can proactively support digestive health with research-proven digestive buffers,” Whitehouse explained.

Evidence also suggests that high-strung horses may benefit from supplemental magnesium and thiamine by reducing anxiety.

*Waitt Wolker, L.H., C.A. Veltri, K. Pearman, M. Lozoya, and J.W. Norris. 2022. Pharmacokinetics of fluoxetine in horses following oral administration. Journal of Veterinary Pharmacology and Therapeutics 45(1):63-68.

Reprinted courtesy of Kentucky Equine Research. Visit ker.com for the latest in equine nutrition and management, and subscribe to Equinews to receive these articles directly.