Wednesday, July 10, 2013

Restricted grazing — does it bring the desired effect in horses?

By Natalija Aleksandrova

Continue the topic on importance of grass grazing for the horse, started here, we will look into a new research of Prof Paul D. Siciliano and his team published recently. The research brings more detailed proof to the fact that restricting a grazing time for a horse to fight her obesity and other metabolic problems, only creates more stress to the metabolism and overall health. When horse's grazing time is limited, she is able to consume more than 3 times more dry matter than normally. Such intensive load of nutrients in a short time stresses the digestive system and the whole metabolism.

Besides the physical stress to the body, it also brings mental stress to the horse. Such horse can never be in peace in a pasture, expecting her time there runs out each moment, and also, if the grazing area is limited to too small, expecting it will be empty of nutrients soon. Also, if the grazing area is limited, it brings additional mental stress to the horses as higher in hierarchy horses continuously chases away lower ones in search for more nutritional grazing spots.

The research

While researchers reported long ago weight lost helps improve horse’s overall health, until now no one hasn’t known exactly what impact restricted grazing has on the equine gastrointestinal health or nutrients intake. A group of North Carolina State University researches, led by Prof Paul D. Siciliano, set a goal to investigate in more detail if restricted pasture access affected horse’s intake rate, energy intake, and hindgut fermentation.

The team separated eight mature idle geldings into four groups and allowed each group pasture access for either 3, 6, 9, or 24 hours for seven days. After seven days, the team reassigned the groups to a different turnout treatment on an ungrazed pasture. By the end of the four-period study, each horse had been subjected to each pasture treatment. When not on pasture, the horses stayed in drylot pens with access to water and salt; horses in the three- and six-hour treatment groups had free-choice access to a low-quality grass hay. Throughout the study, the team recorded the amount of hay consumed and collected fecal samples from each horse on each Day 7.

The team also measured or estimated pasture plant composition, herbage mass (used to quantify pasture available to an animal), grazing height, and forage preference for each period. They noted no difference in digestible energy concentrations (DE) or initial herbage mass for each pasture. However, less pasture was available during periods 2 and 3 compared to 1 and 4.

Key study findings included:
— Horses' total daily dry matter (DM) intake (pasture plus hay, if hay was provided) was not affected by length of turnout time. In other words, horses consumed the same amount regardless of the amount of time they were allowed to graze.
— The team found the highest total daily DM intake — which equaled 1.4% of body weight (BW) — in horses on pasture for 24 hours, which is less than the 2-3% BW previous research suggested. Siciliano and colleagues suggested the lower DM intake in their study could be due to high temperatures seen during portions of the research: High temperatures have been shown to decrease forage intake in horses up to 15-20%.
Pasture DM intake rate increased with restricted grazing. Horses grazing for only 3 hours had a higher intake rate compared to horses grazing for 9 and 24 hours, and horses grazing for 6 hours had a higher consumption rate than horses on pasture for 24 hours.

Amongst their other findings, the researchers also learned that horses' fecal pH — which is both influenced by diet and used as an indicator of hindgut pH — decreased as time on pasture decreased (lower pH means higher acidity); an acidic environment in the hindgut (termed hindgut acidosis) can lead to colic and other health concerns. This showed the team that length of time on pasture affected hindgut microbial fermentation. The authors believed the increase in rate of pasture intake could have played a role in the lower fecal pH, especially when the horses consumed high-quality pasture. However, they stressed, all fecal pH values were within the range considered to be normal.

Average DE intake was greatest when horses were on pasture for 24 hours, but total DE intake did not differ between treatments. The horses consumed 40%, 66%, 67%, and 94% of their total DE requirements with 3, 6, 9, and 24 hours of pasture access, respectively, which indicates that horses increase their rate of consumption with decreased time on pasture.

The team concluded that their findings support the belief that reduced time on pasture increases consumption rate and decreases fecal pH in horses.

“Simply reducing the time a horse spends at pasture may not always be an effective means of decreasing caloric intake,” said Siciliano. The team also noted that more work is needed to develop methods to accurately predict pasture intake of horses grazing for periods less than 24 hours.

The full study, "Effect of Restricted Pasture Access on Pasture Dry Matter Intake Rate, Dietary Energy Intake, and Fecal pH in Horses," is published in June in the Journal of Equine Veterinary Science.


If your pasture is specious enough to provide your horses with enough grazing throughout grazing seasons day and night, horses’ time in the pasture shouldn’t be limited artificially.

Also whenever it is possible, instead of closing your grazing area for recovering of grass there, when this area is limited, rather enough good quality hay should be provided for the horses additionally to grazing. This way the pasture will have a chance to recover naturally, at least to a certain extent, as the horses will choose naturally to eat more the higher quality hay, when the quality of the pasture grazing drops considerably due to overgrazing.

Horses, which are never limited in their grazing time have their life full and happy, finding a lot of other amusement in a pasture besides grazing.

For example, have a rest, including deep sleep:

Or play:

Communicate to each other:

Communicate to people:

Take care of the skin and coat:

Find a herbal help needed:

They move actively:

And, yes, they consume nutrients needed for life:

All photos except no. 12 by Berenika Bratny

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