Study - How Hay Feeder Height Affects Jaw, Neck & Back Posture in Horses

By Monique Warren

​​Hay nets and slow feed hay bags are invaluable and effective tools used to slow the rate of consumption and increase chew time. However, horses are often forced to engage in unnatural feeding positions depending on the height they are hung.

In 2021, Italian researchers conducted a study examining the shape variations of the back, neck, and mandibular (jaw) angle of horses based on specific feeding postures using geometric morphometrics - providing scientific evidence of the adverse physical effects of higher/unnatural eating positions compared to ground level. Read on for a condensed version of their findings. A link to the full study appears in the Reference section below.

Photo: Raspa et al. https://www.mdpi.com/2076-2615/11/3/763/htm

Condensed Highlight of Study

Six warmblood horses were used for the study housed in stalls. All were in good general health and regularly checked for dental disease and ridden regularly.
​
Using video recordings, three positions (CP, LP & HP) were studied to determine the shape variations of back and neck postures as well as the variations of the mandibular angle:
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CP - Control position – Hay on the ground. Considered the natural feeding position. 
Photo: Raspa et al. https://www.mdpi.com/2076-2615/11/3/763/htm

LP – Low hay net position. Neck held below withers height. The bottom edge of the hay net is level with the mid-point of the cannon bone.
Photo: Raspa et al. https://www.mdpi.com/2076-2615/11/3/763/htm

HP – High hay net position. Neck held above
withers height. The bottom edge of the hay net
​level with the horse’s elbow. 
Photo: Raspa et al. https://www.mdpi.com/2076-2615/11/3/763/htm

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Comparison of Low and High Hung Hay Nets

​Frames of horses eating in LP were selected as shown: the position of the yellow line (from the withers to the poll of the neck) formed an angle of 15 ± 3° with the reference line (shown in orange) crossing the withers and parallel to the ground. Photo: Raspa et al. https://www.mdpi.com/2076-2615/11/3/763/htm

Frames of horses eating in HP were selected as shown: the position of the green line (from the withers to the poll of the neck) formed an angle of 15 ± 3° with the reference line crossing the withers and parallel to the ground. Photo: Raspa et al. https://www.mdpi.com/2076-2615/11/3/763/htm

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Shape Variation Points of Reference

​​​​Eight configuration points were used for the back (yellow dots) and seven for the neck (red dots) to map shape variations. The back and neck were analyzed separately. The white arrow indicates the angle between the mandible and  underside of the neck that was calculated for each feeding position. 

Photo: Raspa et al. https://www.mdpi.com/2076-2615/11/3/763/htm

Conclusions

"Our study showed evidence that different feeding positions are able to modify the shape of back and neck postures, as well as the magnitude of the mandibular angle.

When the horse maintained the LP hay net position with the neck 15 ± 3° below the withers, the back posture more closely resembled that exhibited during CP (ground level), considered as a natural feeding position. Instead, no similarity was recorded for both the neck posture and the mandibular angle.

The overall effect on the shape of back and neck postures and mandibular angle was more evident when the horse was forced with the neck 15 ± 3° above the wither height with high hay net position (HP).

Even though the LP hay net position promoted a better back posture, this was not sufficient to maintain a neck posture and a mandibular angle similar to that obtained when a horse was fed from from the ground (CP).

Since hay nets are useful to increase the feeding time consumption, it is necessary to investigate all
the postures that a horse may achieve when feeding out of a hay net and identify the height
which allows a more natural overall posture."

In Closing

The study provided evidence that different feeding positions modify the shape of back and neck postures, as well as the magnitude of the mandibular angle. In closing, I'd like to re-emphasize two key points from the conclusion:

"Even though the low hay net position promoted a better back posture, this was not sufficient to maintain a neck posture and a mandibular angle similar to that obtained when a horse was fed from CP [control position: the ground]."

Because hay nets and slow feed hay bags are useful tools to increase the duration of hay consumption, it is necessary to investigate all postures that a horse may achieve when eating from a slow feeder and identify the height which allows the most natural overall posture. 

Learn more about the physical, mental & emotional benefits of allowing your horse to eat from ground level in a natural grazing position.​
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Helpful Resources

• ​Can Horses Eat More Hay Without Weight Gain?   The Surprising Factors
• Are You a Prisoner of Feeding? Here's How I Broke Free
• How & Where to Test Your Horse's Hay & Interpret Results
• ​9 Benefits of Slow Feeding Horses - Get Slow Feed Savvy
• ​Equine Gastric Acid - 12 Facts You May Not Know​​
• ​Equine Gut Health - The Need for Feed 
• Why Horses Need Salt & Why Salt Blocks Are Not Enough
• ​A Safer Always Have Hay Source – Mature Grass Hay​​
• Sugar Content of Pasture & Hay: Q & A with Katy Watts, Founder of Safergrass.org

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About the Author:
Monique Warren invented the Hay Pillow® slow feeder and is the owner of Hay Pillow Inc.
​Warren has been an equine guardian for over forty years and slow-feed advocate for over 10 years. She contributes equine nutrition and digestive and hoof health articles to publications such as Equine Wellness, The Journal, The Naturally Healthy Horse,  Natural Horse Magazine, Nicker News, Horse Back Magazine, The Horse's Hoof, and  Miniature Horse World Magazine. Equine nutrition and horses feet are her passions. She resides in Southern California.

Reference
Raspa, F.;  Roggero, A.;  Palestrini, C.;  Marten Canavesio, M.;  Bergero, D.; Valle, E. (2021, March 10) Studying the Shape Variations of the Back, the Neck, and the Mandibular Angle of Horses Depending on Specific Feeding Postures Using Geometric Morphometrics. Animals 2021, 11, 763. https://doi.org/10.3390/ani11030763 (open access article). Retrieved from  https://www.mdpi.com/2076-2615/11/3/763/htm