HOW-TO SESSION: FEEDING FOR FITNESS


Evaluating current and past diets is relatively time-consuming but provides details about the horse that help to refine key nutritional goals. For exam- ple, if the 591-kg (1,300-lb) gelding in moderate work was currently consuming 24.6 Mcal digestible energy per day, then recommending a diet that pro- vides 27.6 Mcal (per NRC) would promote weight gain. If the gelding was consuming 24.6 Mcal per day, then a more appropriate energy goal would be 80% of current intake or 19.7 Mcal. Another con- sideration is if the horse’s activity level has changed, as digestible energy provision should match energy expenditure (e.g., reducing concentrate during re- covery and off-season). Some horses are rather effi- cient and require a significant degree of restriction, below 30.3 kcal/lb ideal body weight.17 For the ac- tive horse, severe energy restriction is hopefully not needed and certainly should not be a starting point. Regardless of where the energy goal is initiated (e.g., 27.6 Mcal [NRC moderate work] or 17.9 Mcal [30.3 kcal/kg body weight] for the 591-kg [1,300-lb] geld- ing), the appropriateness of the plan will be deter- mined through strategic monitoring (see Monitoring section).


Generally, a performance horse’s energy needs


can be met by forage, concentrate, or a combination of the two. However, concentrates (e.g., commer- cial performance feeds, grains, and brans) are more energy dense than forages (e.g., 2.6–3.3 Mcal/kg AF) and, thus, are generally not indicated for the over- weight performance horse. Horses generally ob- tain more than 50% of energy requirements from microbial fermentation, specifically volatile fatty ac- ids.18,19 Although the horse in heavy activity is not likely to be able to meet energy needs with forage alone, horses at a lower level of activity and lower energy need are more likely to meet their energy need with forage alone. Furthermore, the insoluble fiber in forage (e.g., cellulose) is slowly fermented by gut microbes, supports a neutral hindgut pH and symbiotic gut microbiota, and thus promotes overall gut health. For this example, if the available grass hay con-


tains 2.0 Mcal/kg DM (0.909 Mcal/lb DM) and 92% DM (average per Equi-Analytical grass hay data20), then the energy density may be converted to an AF basis by multiplying the percent DM (92%)20 by the energy density, 2.0 Mcal/kg DM  0.92  1.8 Mcal/kg AF (0.836 Mcal/lb AF). Notably, forage quality is highly dependent on the stage of maturity at which it is consumed or cut to make hay. Ide- ally, a forage analysis would be conducted and should include an estimate of digestible energy (cal- culated from analyses of crude protein, fat, struc- tural carbohydrates, non-structural carbohydrates [NSCs], and mineral content), neutral detergent fi- ber (NDF), and crude protein. The NDF represents forage cell wall (cellulose, hemicellulose, and lignin) and is a negative indicator of quality and a positive indicator of forage bulk. Therefore, the higher the NDF, the bulkier the forage and thus more filling,


58 2020  Vol. 66  AAEP PROCEEDINGS


Table 4. NRC 20071 Anticipated Dry Matter Intake by Workload Workload


Light exercise Moderate exercise


Heavy exercise and very heavy exercise DM, dry matter; BW, body weight


2


2.25 2.5


Anticipated DM Intake (% BW)


which is helpful for the horse with a high voluntary DM intake.21,22 Anecdotally, grass hay with 70% NDF on aDMbasis is high in that horses may not be able to eat enough to maintain a healthy weight. If the daily energy requirement for the gelding is


17.9 Mcal, then the gelding would need 9.9 kg (17.9 Mcal/1.8 Mcal/kg AF) of this grass hay AF per day, which translates to 9.1 kg (9.9  0.92) or 1.5% of ideal body weight (9.1/591 kg body weight). Con- versely, if the daily energy requirement for the geld- ing is 27.6 Mcal, then feed 15.3 kg (27.6 Mcal/1.8 Mcal/kg AF) of average quality grass hay AF per day, which translates to 14.1 kgDM(15.3 kg0.92) or 2.4% of ideal body weight. Anticipated dailyDM intake for moderate work load is 2.25% body weight (Table 4).1 Therefore, neither scenario is expecting the gelding to consume too much, thus concentrates do not appear to be needed to meet energy needs. Furthermore, both scenarios provide at least 1.5% of BW in DM per day.


Non-Structural Carbohydrates


Diets high in NSCs (includes sugars, starch, and fructan) increase the risk of insulin dysregulation and laminitis, which are associated with obe- sity.23,24 Activity positively influences insulin reg- ulation; thus, active overweight horses may have a lower risk of insulin dysregulation. Regardless, limiting NSCs will likely limit the risk of insulin dysregulation. Although some authors suggest limiting NSCs to 10% of diet DM, the author targets an NSC level lower than the current diet. Forage is lower in NSCs than concentrates, particu- larly grain-based concentrates. Grasses and alfalfa are similar in NSC content, although the high end for grasses is higher than for alfalfa.20,25 Hay may be soaked to reduce water-soluble carbohydrates (sugars and fructan) in forage.26 However, some water-soluble nutrients in the DM are lost. Forage NSCs should be considered along with forage quality and energy density. If feeding based on DM, the forage with the lower NSC concentration would be an ideal choice. In addition to being more energy dense, concentrates are generally higher in NSC than forage, which can reduce insulin sensitivity23 and increase the risk of colic, especially without transition/gradual introduction.27


Nutrient Requirements


The requirements for several essential nutrients are considered to be higher in the athletic horse. Ac-


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