12/11/2024
How do hay nets on round bales impact the axial skeleton of the horse?
You all asked, and we delivered with more research! And I promise it has been worth the wait!
Last week, the second portion of our study evaluating hay nets was accepted into the Journal of Equine Veterinary Science, and this time we teamed up with an equine chiropractor (thanks Dr. Taylor Rieck) to evaluate changes in the axial skeleton!
Introduction: Many horse owners use hay nets. As our last study demonstrated, they have many benefits including a reduction in hay waste and management of bodyweight and body condition scores. Additionally, we were able to explore the impacts on dental health and did not have any concerns regarding soft tissue damage, tooth wear, or dental abnormalities. But that has led us to our next question, can the act of eating hay from a hay net result in changes to the axial skeleton of the horse, specifically relating to the vertebral column?
Materials and Methods: Because I want this post to be able to stand alone (and some of you may have forgotten what we did since the last research post), I will start from the beginning and I apologize for repeating myself. Thirteen mature geldings were used in this study and assigned to treatments based on weight. The study began in September 2021 and all horses received dental work and were assigned to their treatments, seven started on the no hay net control (CON) and six started on the hay net (NET) treatment and all were fed grass round bales. In September 2022, horses received dental work again and switched treatments in the cross-over design. Throughout the study, these horses lived in identical neighboring pens with shelter, ad libitum water, and free choice grass round bales with the only difference being NET horses had their round bale hay placed in hay nets with 1.75”/4.45 cm openings (graciously provided by Hay Chix) while CON horses did not.
During this study, from May through August of both years, changes in the axial skeleton were evaluated. This time frame was chosen as horses were not being worked in undergraduate courses. In May, when the semester ended, an equine chiropractor adjusted all horses to get them to a baseline. Horses were then evaluated for range of motion and pain-pressure thresholds at 4-, 8-, and 12-weeks post-chiropractic adjustment. Cervical range of motion was evaluated using neck stretches for lateral movement as well as chin-to-chest, chin-to-knees, and chin-to-fetlocks. Pain pressure threshold was evaluated at different points on the body using a pressure algometer which documented the amount of pressure applied until the horse moved away to avoid the pressure. Additionally, another chiropractic adjustment took place at 12-weeks and subluxations (misalignment of bones) were documented and rated on a 0 to 3 scale to indicate none, minor, moderate, or severe subluxations. These scores were combined for each location or vertebral region (cervical, thoracic, lumbar, sacral).
Results: There was an average 8% increase in cervical subluxations observed in NET horses (P0.05) and sacral vertebrae were not analyzed as no subluxations were found.
Another finding was that average cervical range of motion was 5 degrees greater in NET horses compared to CON horses for chin-to-chest and chin-to-fetlock measurements (P≤0.05). No differences were observed in pain-pressure thresholds when comparing treatments (P>0.05).
While not the initial objective of the study, we also saw decreased range of motion and pain-pressure thresholds over time regardless of treatment, which suggests the benefits of chiropractic - but I will save this topic for another post when I can dive into into it deeper!
Discussion: Our main findings were a slight increase in subluxations in the neck for NET horses alongside an increase in cervical range of motion. While these findings initially appear to contradict each other, previous research in humans has found that activities which stimulate voluntary neck movements utilizing a wide range of motion and postures can recruit and strengthen cervical muscles. As a result, prehending hay from a hay net may have simulated exercises to strengthen the neck in these horses, however, these movements may have simultaneously resulted in an increase in cervical subluxations.
Conclusions: This study has demonstrated that hay nets do have the ability to influence the axial skeleton of the horse with minor changes. However, the researchers believe that the proven benefits of hay nets, including reduced hay waste, prolonged feeding time, and weight management, outweigh any minor changes in the axial skeleton observed in this study. Additionally, results from this study suggest regular chiropractic work can be beneficial for horses regardless of hay net use!
What Next? While this study gathered some very useful information to create a foundation of knowledge, I would love to investigate hanging net height and hole size to determine how these factors may influence the axial skeleton and time to consumption for horses in the future!
Funding: This study was funded by the University of Wisconsin - River Falls and HayChix.
I hope you find these results as fascinating as we did! There is always so much to learn!
Cheers!
Dr. DeBoer
