Chronic Weight Loss in Horses - Feeding for Weight Gain

Karen E. Davison , Ph.D.

Director, Nutritionist, Equine Technical Solutions

There are many potential causes that can result in a horse having poor body condition. After determining the reason(s) why the horse is losing weight or failing to thrive, implementing a successful weight gain program is a fundamental aspect of returning the horse back to good health. Selecting feed components that maximize digestibility and caloric density of the ration will help to achieve weight gain in a safe an effective manner.

The visual appearance of a horse can be an indicator of overall health and wellbeing.  A shiny hair coat, strong muscle tone, good quality hooves and ideal body condition reflect a strong, healthy horse.   Health and nutrition both come into play in supporting a horse to consistently perform at his best.  Whether performance is measured as athletic activity, growth and development, reproductive efficiency or longevity, top-level performance cannot be sustained by horses in less than top body condition.
A reliable and early visual indication of less-than-ideal body condition is when ribs begin to show.  This indicates that the Body Condition Score (BCS) is < 5/9 on the Henneke Body Condition Scoring System.  If weight loss continues and body fat stores are depleted, muscle tissue will be broken down to generate calories needed for the body to function. Loss of muscle tissue usually occurs first over the back and loin and will eventually affect the neck and larger muscle mass of the hindquarters and shoulders.
If a horse is severely underweight (BCS <3/9) due to inadequate  dry matter intake (DMI), care should be taken to avoid complications related to refeeding syndrome.  Minimum DMI would be estimated at 1% of ideal BW/day (example: 5 kg DMI daily for a horse that should weigh 500 kg at a BCS 5/9) For recommendations and a refeeding plan for starved and malnourished horses, please refer to this article.
Examine the Current Nutrition Program
The first step in determining why a horse is losing weight or failing to thrive would be to examine the nutrition program.
Here are some basic questions to ask:
  • Is the horse properly taking in, chewing and swallowing both feed and forage (hay or adequate pasture)?
  • Is the forage high quality and available in sufficient quantities (minimum of 1.2% BW in Dry Matter Intake)?  
  • Is the concentrate feed appropriate for the horses’ age and activity level?
  • Is the concentrate feed being fed as recommended?
  • Is the horse adequately hydrated?
If the nutrition program is adequate and especially if other horses under the same management and diet are maintaining good condition, further health evaluations would be warranted.  Several health issues including, but not limited to, parasite infestation, endocrine dysfunction, hepatic disease,  renal disease, chronic pain, and chronic use or misuse of certain medications can contribute to chronic weight loss or horses being harder keepers.

Provide Additional Calories for Weight Gain
Feeding to achieve weight gain requires higher daily calorie intake than feeding to maintain good condition in the same horse at the same level of activity.  The number of calories required may vary due to many factors such as individual metabolism, climate and stress level, as well as the composition of the weight gain (i.e. adipose tissue or muscle) and the composition of the diet.  Supporting gain to change a horse from a BCS of 3 to 5 will be different than changing that same horse from a BSC of 5 – 7.  When the starting BCS is below 5, the weight gain involves increasing muscle mass as well as gaining body fat stores.
Estimates for digestible energy (DE) required to induce weight gain have been derived from limited data and not proven under controlled conditions.  These estimates, shown in Table 1, are a good starting point but may over- or under-estimate the amount of DE needed to change the BCS of an individual horse, particularly those that currently score toward either end of the BCS scale.
Table 1.  Estimated Increase in Digestible Energy (DE) Intake Necessary to Change the Condition Score of a 500 kg horse from a 4 to a 5a
Time Period to Accomplish Gain DE above Maintenance (Mcal/d) Percent Increase in DE above Maintenance
60 days 5.3 – 6.7 32 – 41 percent
120 days 2.7 – 3.3 16 – 21 percent
180 days 1.8 – 2.2 11 – 14 percent
Table adapted from Nutrient Requirements of Horses, 6th ed., NRC 2007
a Assumptions: 1 unit of change of condition score requires 16 – 20 kg of gain and 1 kg of gain requires 20 Mcal DE above maintenance.
Using these values to implement a weight gain program requires a good estimate of the DE required for maintenance, which can also be an inexact science.  DE recommendations for horses of various ages, activity levels and body weights are published in the 2007 NRC (Table 2) or available at
Table 2. Daily maintenance DE requirements* of mature horses (NRC 2007)
Desired bodyweight (kg) Minimum (Mcal) Average (Mcal) Elevated (Mcal)
400 12.1 13.3 14.5
500 15.2 16.7 18.2
600 18.2 20.0 21.8
900 27.3 30.0 32.7
*Minimum maintenance applies to sedentary horses due to confinement or limited voluntary activity, average refers to alert horses with moderate voluntary activity, and elevated applies to nervous horses or those with high levels of voluntary activity.
In chronic weight loss cases, the DE for maintenance would be reasonably estimated as the Mcal/day the horse has been consuming to ‘maintain’ their current poor condition.  A good starting point would be to establish a history of the situation and estimate the daily DE provided by the diet the horse has been eating  over the past few months. 
The specific weight gain program for each case may be different depending on resolution of health issues, current volume of intake, ongoing activity level and the goals for when that weight gain is accomplished.  The general recommendation for safe rates of gain would be roughly 0.2 – 0.7 kg/day. 
Designing a weight gain program may simply involve increasing the amount of the current feed and forage being fed.  For significant or more rapid weight gain, incorporating higher calorie feeds and forages into the diet will provide the needed additional Mcal/day in a smaller volume.  That may be important for horses who are already consuming above 2.5% of BW in DMI/day or horses that can’t or won’t eat a large volume. Table 3 provides examples of different feed quantities that provide approximately 4.0 Mcal, which if added to the horse’s current ration, would support an estimated 0.2 kg of weight gain/day.
Table 3.  Diet Options That Provide Approximately 4.0 Mcal
Diet Component or Purina Feed Product Quantity to provide 4.0 MCal
Average Quality Warm-Season Grass Hay 2.5 kg
Good Quality Alfalfa Hay 2.0 kg
Stabilized Rice Bran 1.0 kg
Vegetable Oil (soy, corn, canola, flax, etc.) 16 ounces (2 cups)
Purina Ultium Competition Formula 0.95 kg
Purina Omolene 200 Performance 1.12 kg
Purina Amplify High-Fat Supplement 0.90 kg
High quality forage, from hay or pasture, should be the foundation of a successful weight gain program.  When good quality forage isn’t readily available, utilizing a Purina complete feed to replace a portion or all of the forage will provide excellent quality fiber and needed calories. Table 4 provides the DE values for select Purina feeds, complete feeds and additional fiber and hay sources.  These items are presented in in descending order of Mcal /lb value.  The DE values for all Purina horse feeds can be found in this quick reference chart
Table 4. Digestible Energy Value (Mcal/lb) of Select Purina Feeds and Other Diet Components
Purina Product or Forage Source Digestible Energy (Mcal/lb)
Amplify (supplement) 2.00
Ultium Competition 1.90
Ultium Gastric Care 1.70
Omolene 500 1.65
Omolene 200 1.62
Equine Senior Active 1.60
Omolene 400* 1.40
Equine Senior* 1.20
Impact Hay Stretcher* 1.00
Beet Pulp 1.00
Alfalfa Hay (good quality) 0.95
Grass Hay (good quality) 0.80
*Complete feeds with appropriate amounts and types of fiber to replace a portion or all of the hay or pasture.  Can be used as a higher calorie forage source or supplement to lower quality forage sources.
One important consideration may be to help clients understand that horses in less-than-ideal condition may not feel very good, they may have been “quieter” and easier to manage.  A horse that has been sick, hurt or thin is often lethargic, especially if they’ve been on a low plane of nutrition. When the health issue is resolved, the horse is no longer in pain and is being fed properly, they may start feeling much better and initially the owner may feel like their horse has too much energy.  Most often, a horse that begins to feel better will adapt to the new plane of nutrition and mentally level out within 30 – 45 days.   The goal is for them to feel good and be sound and healthy, which ultimately helps the nervous energy to subside.
Achieving weight gain and bloom requires providing additional calories in a well-balanced diet complete with essential amino acids, fatty acids, vitamins and minerals.  All these nutrients play a role in hair coat, muscle tone, hoof quality, immune function and over-all appearance and health.  Fat supplements provide very efficient calories to support weight gain, but those calories can only support gains in body fat.  Regenerating lost muscle and improving hair coat and hoof quality requires complete and balanced nutrition.

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