HOW-TO SESSION: FEEDING FOR FITNESS


total daily ration when possible.5 Forage require- ments can be met by both preserved forages (long- stemmed hay, hay pellets, chopped hay, and commercially available forage-replacement alterna- tives) and fresh pasture. Forage intake while on pas- ture can vary greatly, and total dry matter intake while grazing is dependent upon several factors, in- cluding total hours of access and overall pasture qual- ity. Studies have shown that horses allowed 4 hours or less of daily pasture access will consume 0.220.02 kg DM/100 kg BW/hour, and horses allowed more than 4 hours of daily pasture access will consume 0.11  0.02 kg DM/100 kg BW/hour.6 For example, if a 500-kg horse were allowed to graze on pasture for 6 hours per day, dry-matter intake would be expected at 3.3 kg, which is equivalent to approximately 3.7 kg hay (as-fed basis). Chewing long-stemmed forage increases saliva output, and saliva contains bicarbonate, which helps to buffer acid secretions in the stomach.7 Maximiz- ing access to forage will increase time spent chew- ing, as well as potentially decreasing boredom and stress while confined. Horses in a natural setting are estimated to graze for approximately 14 hours each day.8 When stalled, the horse’s opportunity to forage is limited, and the utilization of small-hole hay nets (3.2-cm and 4.4-cm openings) as opposed to feeding from the stall floor is an effective way to increase the overall time to consumption of hay and better mimics grazing conditions.9 Perhaps the most significant feature of forage in


terms of digestive health is that it supplies the fer- mentable fiber required by the hindgut microbes to function properly. When feeding a hindgut fer- menter such as the horse, maintaining a healthy population of hindgut microorganisms plays a criti- cal role in not only digestion, but overall horse health. Together with their genetic material and interactions with each other in their environment, these hindgut microbes are a part of a diverse and complex ecosystem referred to as the “equine micro- biome.” The importance of a healthy microbiome environment cannot be overstated, and recent ad- vances in laboratory techniques and gene sequenc- ing technology have made it easier to isolate, identify, and quantify the specific organisms present in the horse’s hindgut. The newest frontier in equine nutrition research involves delving into the equine microbiome, and scientists are currently working to characterize what both a healthy and unhealthy equine microbiome looks like, in addition to how that microbial ecosystem can be manipulated to improve horse health and performance.10,11


Concentrates


The demands of exercise and performance increase digestible energy and nutrient requirements of the horse. When forage alone cannot meet these increased demands, a concentrate feed will be re- quired to meet the nutritional needs of the perfor- mance horse. Concentrates include cereal grains


62 2020  Vol. 66  AAEP PROCEEDINGS


like corn, oats, and barley, as well as commercially available pelleted and textured grain mixes. When appraising the impact of concentrates on digestive health, meal size, and composition are important factors to consider, especially in relation to prevent- ing starch overload in the hindgut. The horse’s small intestine is well suited to digest starch, a useful energy source for many performance horses, up to a certain point. Many studies have at- tempted to elucidate the upper limit of small intes- tinal starch digestion to prevent starch from reaching the hindgut. Small intestinal starch di- gestion varies somewhat with cereal grain source (i.e., oat starch is more digestible than barley starch) and processing (i.e., mechanical and hydrothermal), but a general guideline is to limit starch intake, regardless of the source, to 2 g/kg BW/meal in order to prevent starch overload and rapid fermen- tation in the hindgut.12,13 Practically, this trans- lates into feeding no more than a 2.5 kg meal of a cereal grain-based concentrate (40% starch) for a 500-kg horse (or, limiting meal size to 0.5% of the horse’s BW). Limiting the starch content of a meal even further may be warranted in certain circum- stances (i.e,. in horses with insulin dysregulation or gastric ulcers), but this is a good benchmark goal for most healthy performance horses. For horses that are prone to bolting or rushing their concentrate meals, feeding hay before the concentrate meal can also help to slow the rate of intake.14 Concentrate composition will also dictate the total amount of starch contained in a meal. Concentrate meals consisting of straight cereal grains will con- tain the highest concentration of starch, while multi-ingredient rations and commercially available products will vary considerably depending on the proportion of ingredients in the ration or feed for- mulation. Book values for cereal grains are readily available, and if the starch level of a commercially available horse feed product is not listed on the feed tag, the manufacturer should be able to provide that information upon request. Many commer- cially available products for performance horses con- tain added fat and fiber, which are used as additional sources of digestible energy. This is gen- erally positive in terms of digestive health, as it reduces reliance on starch to serve as the primary energy source, as well as supplies additional digest- ible fiber. For horses with elevated energy require- ments, feeding fat- and fiber-added rations increases the energy density of the diet and in most cases is a recommended practice. However, there is an upper threshold for small intestinal fat digestion that, if exceeded, can reduce the digestibility of certain nu- trients. The inclusion of fat at up to at least 10% of total dry matter intake (forage  concentrate) ap- pears to have minimal negative impact on digestive health.15 Because forages are naturally low in fat (1% to 3% DM basis), exceeding this level of fat in the total ration is not common, even with the use of high-fat concentrate feeds (10% to 14% fat).


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