Meeting a horse’s nutrient requirements is critical to their health. Horse owners should understand the basics of nutritional management, and how to supply adequate nutrient amounts.
As a practicing equine nutritionist, I often get questions about nutrient requirements – how are they determined? What are these amounts based on?
How a nutrient requirement has been established largely depends on the individual nutrient, but this article will dive into some of the science behind our current understanding of equine nutrient requirements.
Established Nutrient Requirements
In North America, the Sixth Revised Edition of the Nutrient Requirements of Horses (NRC, 2007) is primarily what is relied upon to balance rations. This text is a project of the Board on Agriculture and Natural Resources of the National Academics. This publication reviewed the existing scientific literature relating to equine nutrition and summarized it relating to nutrient requirements.
It is important to understand that our scientific understanding of what is ideal for horses is continually expanding and most of the research has used light breed horses (Thoroughbreds, Quarter horses and Standardbreds). Additionally, in cases when there is no equine research, information has been extrapolated from other species.
Let’s use protein as an example; protein is comprised of chains of amino acids and are a major component of body tissues. The equine dietary requirement is specifically for amino acids, not protein. However, aside from the amino acid lysine, requirements for the other essential amino acids have not been established. Therefore, a crude protein (CP) requirement is relied on.
Crude protein is a measurement of the total nitrogen content within a feed, or ingredient that has been converted into the estimated protein amount. This requirement for horses has been established through the analysis and summarization of numerous nitrogen balance studies. For an average horse that is not in work the equation ‘body weight (BW) X 1.26 g CP/kg BW/day’ is used.
Note that this does not guarantee that the horse is consuming adequate amounts of the required essential amino acids. It is recommended that the lysine requirement be 4.3% of the horse’s crude protein requirement. This example highlights that there is truly always more to know when it comes to horses, and relying on the most up-to-date scientific literature is recommended, but as a horse owner, it is also important to understand that there are gaps in the science.
Mineral Amounts & Ratios
Understanding what equine science looks like, and how the process results in industry changes is fascinating to me, and it is knowledge that I feel is valuable to share with horse owners.
In addition to simply providing enough of each essential nutrient, ratios also come into play. For example, the ratio of zinc to copper must also be considered alongside the amount of each mineral fed as zinc competes for the same transport mechanisms. Too much zinc in relation to copper can cause a deficiency in copper.
Studies have demonstrated that a diet containing 40 mg Zn/kg adequately supported growing foals and maintained normal body stores of zinc. Other publications have demonstrated that 50 mg Zn/kg dry matter (DM) was adequate for all classes of horses. At the time of publication of the NRC, 2007, no controlled studies supported a dietary zinc requirement greater than 50 mg/kg ration DM.
Additionally, there have been publications calculating the true digestibility of zinc to be 20.8 percent, resulting in the requirement of dietary zinc to be lower than the current recommended requirement, however with a lack of long-term studies demonstrating that health issues do not arise when a lower amount of zinc is fed to horses the committee decided to keep the requirement at 40 mg/kg DM.
Recent Publications
Now, as previously mentioned, new science is being published regularly. A 2023 study (van Bommel-Wegmann et al.) investigated the effects of dietary zinc chloride hydroxide and zinc methionine on the immune system of healthy horses and ponies. The equids were fed a diet meeting maintenance requirements, 120 mg zinc/kg DM and 240 mg zinc/kg DM.
The study illustrated that both the dietary zinc dose and compound did have an effect on selected immune variables in healthy adult horses and ponies – however depending on the source, both activating and lowering effects were detected. It should also be noted that the sample size of this study was relatively small (8 ponies, 2 horses).
Will newer research impact the next publication of the Nutrient Requirements of Horses? Yes, of course, however, is this enough information to warrant increasing your horse’s dietary zinc levels? Right now, I don’t think so.
A lot goes into establishing nutrient requirements, from the scientists performing the studies, to the National Research Council Committees summarizing and reviewing the information. Staying tuned in to the recent publications is of course interesting and critical to maintaining relevance as a professional, but exercise caution on making changes to your horse’s program because of anecdotal evidence on online forums or based on singular studies.
Take Home Message
The next time you are reading anecdotal evidence on an online forum, or a summary of one singular research study I would like you to think about the scientific process that goes into establishing nutrient requirements and recommendations for best practices. Working with professionals that maintain relevance regarding recent scientific work, while understanding the limitations is beneficial to building a science-backed program for your horse.
Interesting in having your horse’s ration evaluated to ensure their nutrient requirements are met? Inquire here for a balanced diet.
By: Madeline Boast, MSc. Equine Nutrition, PAS
References:
van Bömmel-Wegmann, S., Zentek, J., Gehlen, H., Barton, A. K., & Paßlack, N. (2023). Effects of dietary zinc chloride hydroxide and zinc methionine on the immune system and blood profile of healthy adult horses and ponies. Archives of animal nutrition, 77(1), 17-41.
National Research Council. 2007. Nutrient Requirements of Horses.
