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Tips for Weight Gain for Horses

Ideally, to know how many calories your horse needs to increase body condition score, it’s necessary to know how many calories your horse currently consumes (from grazing, hay, concentrates, and supplements) and take into account its age, level of work, additional energy requirements (breeding, lactation, pregnancy, etc.), and with consideration of how easily your horse gains and loses weight.  If that’s overwhelming… work with your readily available equine nutritionist at Science Supplements to come to this estimation. For horses who are significantly underweight or who have additional health concerns (teeth, GI tract disturbances, metabolic disorders, pregnancy/lactation, chronic medications, etc.), please consult with your veterinarian and nutritionist regarding feed changes and weight gain.  Further, for horses who are seemingly being fed enough to meet their demands but continue to have difficulty gaining weight, the health of the stomach, hindgut, and overall digestive tract could be compromised and need additional support to help increase feed digestion and nutrient absorption. 

We’ll focus here on feeding the otherwise healthy but mildly underweight horse to gain 1-2 body condition scores with the goal of reaching a moderate score on a scale of 1-9 (Henneke et al., 1983).  For a horse who is not currently losing or gaining weight, (weight is holding steady), a simplistic diet adjustment to gain weight would be increasing feeding (gradually) to 160% of the calorie content of the current diet, which has been shown to result in approximately 44 lbs (20 kg) of weight gain over 42 days and may result in an increase of 1 body condition score (Gill et al., 2017).  In adding feed to your horse’s diet, it’s important to maintain a higher ratio of forage to concentrate, as the majority of intake should always come from forages like grass, hay, or hay/alfalfa cubes to maintain health of the equine GI tract and beyond.  Of note, even when a concentrate is forage based – like pelleted grass – the risk of ulcer development is increased over long-stemmed forages (Flores et al., 2011). The National Research Council recommends a minimum 1% of body weight in forage per day and goes on to associate high concentrate diets with behavior issues, ulcer development, hindgut disturbances, laminitis, and more (National Research Council, 2007).  For this reason, if weight gain is your goal, start with evaluating your horse’s forage intake amount and percent of diet first, and if appropriate, increase forage intake as your first step in diet adjustment.  How this is accomplished depends on what type of forage your horse receives – such as increasing turn out time, allowing access to higher quality/lower maturity grasses, increasing amount of hay, providing an additional hay meal during the day, adding in or substituting higher quality hay like alfalfa, etc.

For weight gain itself, the amount of calories provided by the diet is more important that the source, as either high fat/high fiber or high starch/sugar isocaloric diets result in similar increases in body condition score (Suagee et al., 2008). However, high starch/sugar diets are associated with increased wood chewing and cribbing behavior (McGreevy et al., 1995), aggression when feeding (Zeyner et al., 2004), substantial microbial and pH changes in the hindgut (Medina et al., 2012), and increased risk of laminitis and colic (Garner et al., 1978), while supplementing diets with oil is associated with lower body heat production in hot weather (Kronfeld et al., 1996), reduced feed volume and water needs in hot weather (Kronfeld et al., 1996), reduced startle response, excitability, and nervousness (Holland et al., 1996; MacLeay et al., 2000), improved utilization of fat soluble vitamins (Kienzle, 2003), lower glycemic and insulin responses to feeding (Williams et al., 2001), and reduced risk factors of ulcer development (Cargile et al., 2004), making adding oil to the diet a beneficial and safer way to increase body weight and body condition score than adding high starch/sugar feeds like typical grain based feeds. 

Further, adding oil is relatively easy and low cost, but all fats are not created equal.  While most are approximately 120 calories per tablespoon (1920 calories per cup), one variation of interest comes from the ratio of Omega 3 (anti-inflammatory) to Omega 6 (pro-inflammatory).  While Omega 6 has its place in the horse diet, the average equine diet provides sufficient or excessive Omega 6 and is lacking Omega 3.  For that reason, I always suggest seeking an oil with a high ratio of Omega 3 to Omega 6.  While fish oils are the best with a ratio as much as 21:1, the flavor of fish oil makes it an un-practical top dressing for equine feeds.  Linseed/flaxseed oil is both palatable and a ratio of 4.1:1, though it can be hard to source and expensive to ship, and you’ll have to be conscientious of its shelf life.  Hemp seed oil is receiving attention for its ratio of 3:2, but again sourcing may be an issue, cost is relatively high, quality could be questionable, and – while typically only minimal banned substances may be within hemp seed oil – as a fat soluble nutrient, the clearance time is uncertain and in some circumstances could result in a positive banned substance test.  For the best “over the counter” ratio, canola oil comes in at 1:2, is very easy to locate, inexpensive, and inert in flavor.  When adding oil to your horse’s feed, start with ¼ cup per day, split between meals ideally, and increase the amount over the course of a few weeks up to 1 cup per day, for a typical 1100 lb horse.  As you are increasing, however, keep tabs on your horse’s fecal consistency, as some horses may develop lose stools as oil is increased.  If this happens, reduce the amount back to where fecal consistency returns and hold the amount there.

So with that in mind, if your goal for your horse is increasing their body weight and after evaluating their current diet, aim to increase forage and fat content first, as these will provide additional calories in the safest way.  After gradually increasing these components and giving your horse a few weeks to show signs of weight gain, if the results are not progressing as quickly or effectively as needed, then consider adding additional concentrate feeds – ideally still in the higher fat/higher fiber classification, such as linseed/flaxseed meal, senior/complete feeds, or commercial feeds specifically designed to be higher in fat and fiber. 

See our Stomach, Hindgut, and Digestion Category 

Cargile JL, Burrows JA, Kim I, Cohen ND, Merritt AM. Effect of dietary corn oil supplementation on equine gastric fluid acid, sodium, and prostaglandin E2 content before and during pentagastrin infusion. Journal of Veterinary Internal Medicine. 2004;18:545-549

Flores RS, Byron CR, Kline KH. Effect of Feed Processing Method on Average Daily Gain and Gastric Ulcer Development in Weanling Horses. Journal of Equine Veterinary Science 2011;31(3):124-128.

Garner HE, Moore JN, Johnson JH, Clark L, Amend JF, Tritschler LG, Coffmann JR, Sprouse RF, Hutcheson DP, Salem CA. Changes in the caecal flora associated with the onset of laminitis. Equine Veterinary Journal. 1978;10:249-252

Gill JC, Lloyd KE, Bowman M, Siciliano PD, Pratt-Phillips SE. Relationships Among Digestible Energy Intake, Body Weight, and Body Condition in Mature Idle Horses. Journal of Equine Veterinary Science. 2017;54:32-36

Henneke D, Potter G, Kreider J, Yeates B. Relationship between condition score, physical measurements and body fat percentage in mares. Equine Veterinary Journal 1983;15:371-372

Holland JL, Kronfeld DS, Meacham TN. Behavior of horses is affected by soy lecithin and corn oil in the diet. Journal of Animal Science. 1996;74:1252-1255

Kienzle E, Kaden C, Hoppe PP, Opitz B. Nutrient digestion coefficients. Journal of Animal Physiology and Animal Nutrition. 2003;87:174-180

Kronfeld DS. Dietary fat affects heat production and other variables of equine performance under hot and humid conditions. Equine Veterinary Journal. 1996(Supplement 2):24-34

MacLeay JM, Valberg SJ, Pagan JD, Billstrom JA, Roberts J. Effects of diet and exercise intensity on serum CK activity in thoroughbreds with recurrent exertional rhabdomyolysis. American Journal of Veterinary Research. 2000;61:1390-1395

McGreevy PD, Cripps PJ, French ND, Green LE, Nicol CJ. Management factors associated with stereotypic and redirected behavior in the thoroughbred horse. Equine Veterinary Journal. 1995;27:86-91

Medina B, Girard ID, Jacotot E, Julliand V. Effect of a preparation of Sacchromyces cervisiae on microbial profiles and fermentations patterns in the large intestine of horses fed a high fiber or high starch diet. Journal of Animal Science. 2002;80:2600-2609

National Research Council. Nutrient Requirements of Horses: Sixth Revised Edition. 2007. Washington, DC: The National Academies Press

Suagee JK, Burk AO, Quinn RW, Petersen ED, Hartsock TG, Douglass LW. Effects of Diet and Weight Gain on Body Condition Scoring in Thoroughbred Geldings. Journal of Equine Veterinary Science. 2008;28(3):156-166

Williams CA, Kronfeld DS, Staniar WB, Harris PA. Plasma glucose and insulin responses of thoroughbred mares fed a meal high in starch and sugar or fat and fiber. Journal of Animal Science. 2001;79:2196-2200

Zeyner A, Geibler C, Dittrich A. Effect of hay intake and feeding sequence on variables in feces and faecal water (dry matter, pH value, organic acids, ammonia, buffering capacity) or horses. Journal of Animal Physiology and Animal Nutrition. 2004;88:7-19

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