The Chew Factor - Fibre Intake in Horse Hay
Why choosing hay for fibre content can be important.
By Shelagh Niblock, PAS
Horse owners are becoming very familiar with maneuvering their way through a lab report describing the nutrient content of hay. Terms such as dry matter (DM), crude protein (CP), water soluble carbohydrates (WSC), and non-structural carbohydrates (NSC) are routinely assessed by horse owners looking to buy a hay that works for their barn. Owners of horses with metabolic issues, such as equine metabolic syndrome (EMS), insulin resistance (IR), or pituitary pars intermedia deficiency (PPID) know that having an understanding of the significance of the analytes on a hay analysis is a tool they can use to make good feeding decisions for their horses.
A lab analysis report for hay can be a gold mine of good information for horse owners, providing far more than just moisture, sugar, and protein. A basic near-infrared spectroscopy (NIRS) lab analysis will also provide reasonably accurate information on the minerals present — calcium (Ca), phosphorus (P), magnesium (Mg) and potassium (K) — in your hay. Computer generated calculations will provide you with the digestible energy (DE), which is an estimate of the amount of energy the hay might provide your horse. But what about the values ADF and NDF? What do these numbers reported on your hay analysis mean? Can they help you make feeding decisions for your horse?
What are ADF and NDF?
All plants cells are composed of cell walls and cell contents. The plant cell contents contain the protein, sugars, and most of the fats in the plant. The plant cell walls contain the fibre or complex carbohydrate fractions. The proportions of the cell wall relative to the cell content are expressed on your hay analysis as acid detergent fibre abbreviated as ADF, and the neutral detergent fibre abbreviated as NDF. The terms ADF and NDF, used to describe the plant cell walls, in fact refer back to the laboratory procedures used to measure them. Both ADF and NDF are terms used to quantify fibre and they are related to each other in that ADF is actually a part of NDF.
Growing grass plants become taller with a greater stem-to-leaf ratio as they seek to reproduce. A seed head on a mature grass plant must be supported by a strong fibrous stem to ensure seed is distributed in the environment by wind, birds, or animals. As the plant matures and gets closer to producing a seed head, the plant cell contents decline and the plant cell walls increase proportionately. That also means that as the plant matures the protein and energy go down and the ADF and the NDF go up. The stems, which are of course what we feed our horses as hay, become more coarse and fibrous as the grass matures, and the high nutrient contents of the cell get transferred into the seed head. This helps to ensure the plant can reproduce, but for those of us looking for hay it does mean that the maturity of the forage will have a significant bearing on the nutrients it brings to our horses.
ADF values in a grass hay will vary from approximately 30 percent on a dry matter basis up to over 40 percent depending on maturity. NDF values are generally about 20 percentage points higher than ADF values on a grass hay and about eight percentage points higher on an alfalfa hay. In other words, if you buy a grass hay with an ADF of 37 percent the NDF will typically be approximately 57 percent. An alfalfa hay with an ADF of 37 percent will typically have an NDF of about 45 percent. Mixed stands of forage will have an NDF of somewhere in between depending on the proportion of grass to alfalfa in the cut.
Grass hays with an ADF of less than 35 percent will typically be green, fine, and soft with high digestibility. These are the kinds of hay that your horse will seem to inhale while your back is turned. Hays like this are particularly good for seniors and/or young growing horses with small mouths and deciduous teeth. A first cut timothy, which is considered to be ideal for horses, typically has an ADF between 35 percent and 40 percent on a dry matter basis. First cut timothy is usually more coarse and full of seed head, but it is still very palatable, which translates to a much slower intake and fewer bored horses in the barn with little waste.
A 500 kg horse takes approximately 3,500 chews to eat one kg of hay in about 40 minutes. Coarser hay takes longer to chew and produces more saliva, which helps to neutralize stomach acid. Photo: iStock/DebraCarrPhotography
Related: Nutrient Requirements of Horses
How does ADF and NDF affect my horse?
ADF and NDF can tell us something about the expected feed intake and chewing behaviour of our horses when they are eating. Hay that is very low ADF can have high energy content and can be consumed very quickly. Once consumed, that hay will have high digestibility delivering a lot of nutrients to the horse. Horses that are being fed hay free choice can quickly eat far more of a low ADF hay than they need. That extra energy intake can lead to overweight horses, not to mention a big feed bill. Trying to limit the intake of a lower ADF hay can result in bored unhappy horses in the barn.
Feeding a higher ADF hay means slower feed intake due to the additional chewing needed. This might be just what you need if you have a barn full of horses with moderate nutrient needs but it can present problems for horses with higher nutrient needs, such as growing horses or performance horses. A high ADF hay, however, might not be suitable at all for a senior with poor teeth.
Fibre affects feed intake and chewing
Chewing is a very important part of the life of a healthy horse. The amount of chewing the horse does is dictated by what he or she is eating. Forage generates more chewing than concentrate does, and it takes more time for the increased chewing necessary to break the particle sizes of forage down to pieces small enough to swallow. Estimates of chewing time for different feeds have been measured by many research groups, but typically, a 500 kg horse can eat one kg of hay in about 40 minutes, taking approximately 3500 chews to do the job. On the other hand, the same horse eating 1 kg of whole oats will need to chew about 850 times and can consume them in about ten minutes.
Chewing also limits intake. It takes your horse longer to consume a coarse mature hay than a fine early cut grass hay. Hay with an ADF of between 35 and 40 percent will be more mature and have more “chew” to it than a second or third cut grass hay, which was cut early and is all leaves.
More chewing also generates more saliva. Saliva contains bicarbonate which helps to buffer the stomach which produces acid continuously. It is a fact that horses on high forage diets, even if stalled, have fewer problems with gastric ulcers than those who have high concentrate diets.
Does teeth floating impact chewing in horses?
Because of dietary differences, horses wear their teeth down faster in the wild than they do as domesticated animals. This can result in the teeth of our domesticated horses wearing unevenly, creating the potential for “waves” and “hooks” on the teeth. Regular dental check-ups and intervention by your veterinarian are important to keep teeth functional.
A recent scientific paper presented at the 2021 Virtual Equine Science Society (ESS) Conference showed that dental intervention by floating affected the chewing amplitude per minute, length in chewing time per mouthful, and the strength of the chews of mixed diets including hay and concentrates. The data indicates that dental floating does affect chewing behaviour, possibly improving feed mastication, intake, and digestibility (1).
Managing the forages in your barn using a lab report
It’s easy to see where typical equine diets containing a combination of concentrates and forage could leave the stalled horse with a lot of free time to get into trouble! Horses with feed in front of them tend to be more content and have less anxiety than those who do not. Nevertheless, feeding free choice forages is not always the answer for many horses. Some horses are “eating machines” and will get fat if allowed to eat all day, even with innovations like slow feeder hay nets. Your choice of hay can be a very significant factor in how much chewing you can provide for your horse. Hay that is a little more mature, and is a little more coarse with a higher ADF and NDF, can often be just what you need for a barn full of happy horses with lots of chewing to do.
An interesting scientific paper by a Swedish researcher looked at the influence of plant maturity at harvest of haylage on equine ingestion times and ingestive behaviour. The findings suggest that the more mature the forage, and the higher the ADF and NDF, the longer it takes for horses to consume the same amount of feed due to increased chewing time needed (2). This is good news for those of us who want to keep our horses busy eating without gaining excess weight; on the other hand, it means that more mature forages with higher ADF and NDF values might not be suitable for senior horses, growing horses with deciduous teeth and small mouths, or performance horses where nutrient intake is critical for performance. If you need to maximize the nutrients provided to your horse with good hay, then you should be looking for lower ADF and NDF values on your hay analysis.
Start using the ADF and NDF analyses on your hay test to select the right forage for your barn. If you have a metabolic horse you will be accustomed to choosing hay based on NSC content, but a hay with a low NSC and a low ADF/NDF value might need to be more carefully managed than a hay with a slightly higher NSC and an ADF of closer to 40 percent. That coarser hay will take longer to eat and will provide more chewing for your horse. He or she will be happier and probably healthier, with less blood glucose and insulin swings provided by slow consistent feed intake and lots of chewing.
Make sure you get your horse’s teeth floated regularly when feeding a coarser feed. Waves and hooks on teeth can reduce feed intake and digestibility, not to mention creating bitting issues. And remember that good forage is the foundation of any equine diet, delivering safe energy and nutrients, and likely most important, a happy horse.
Related: Iron in the Equine Diet
(1) Jacobs, R.D., et al. 2021. Equine chewing is influenced by dental intervention in the Journal of Equine Veterinary Science, Volume 100.
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