Why Fat-Enhanced, Lower Starch Diets Help Maximize Athletic Performance:

Matching the Physiological Effects of Conditioning to the Diet

of the Elite Performance Horse.

 Dr. Daniel J. Burke, Ph.D., Director of Tribute Equine Nutrition at Kalmbach Feeds 

There are a number of ways to define physical fitness. Below are (3) possibilities: 

PHYSICAL FITNESS 

1. Increased capacity to perform work while increasing the efficiency that work is performed.
2. A smaller disturbance in homeostasis (i.e. heart rate, blood parameters) during work.
3. Faster return to normal resting state after performing work. 

A horse becomes more fit due to physical and biochemical changes elicited by exercise over time.  This paper will review some of these changes and how horse diets can maximize the benefits of the biochemical responses to short and long-term exercise. 

TYPES OF EXERCISE

There are two main types of exercise, with a great range in between. The first is maximal exercise, which is; work of high-intensity for a short period of time, such as sprint racing. The main substrate used to supply energy in maximal exercise is carbohydrate (CHO).  The second type of exercise is submaximal exercise, which is; work of low-intensity for a long period of time, such as endurance racing.  Obviously, there a many types of exercise that fit between maximal and submaximal, like; dressage, jumping, longer races, etc.

In a fit horse, the major energy substrate is fat.  The preferred energy substrate would depend on how close to maximal or submaximal of the work performed.  The energy substrate preference changes as the horse becomes more fit, allowing a greater portion of the exercise bout to utilize fat, sparing CHO and lessening the production of lactic acid, the end-product of CHO metabolism in the muscle. The end-products of fat metabolism are CO₂ and water – Much less disturbing to acid/base balance. 

SHORT-TERM RESPONSE TO EXERCISE

During a single bout of exercise, many physical and biochemical events take place in the horse’s body.  The response to short-term exercise is different in fit versus unfit horses. The unfit horse’s muscle seems to prefer CHO as a substrate, whereas the fit horse’s muscle prefer fat over CHO for a greater portion of the work. 

SHORT-TERM RESPONSE OF BLOOD PARAMETERS TO EXERCISE:

Increased lactic acid concentration (correlates to the intensity of exercise and fitness of the horse).

·         Increased packed-cell volume (PCV).

·         Increased CO₂ concentration.

·         Increased mobilization of free-fatty acids (FFA) (especially in submaximal exercise)

·         Decreased O₂ concentration and decreased pH.

·         Decreases in some electrolytes.

SHORT-TERM RESPONSE OF MUSCLE PARAMETERS TO EXERCISE:

·         Glycogen and glucose major energy substrates (especially early in exercise and during intense exercise).

·         Decreased glycogen concentration.

·         Increased lactic acid concentration (may be 2-3x blood values).

·         Increased use of FFA during submaximal exercise.

FATIGUE

Causes of fatigue are poorly understood and are very complex. A simple explanation is that during maximal effort, fatigue is related to waste product accumulation, especially lactic acid. The end-product of CHO metabolism.

During submaximal exercise, fatigue appears to be related to substrate depletion, most likely glucose or glycogen.

DELAYING FATIGUE

Glycogen Loading:

Increases the muscle stores of glycogen. This can be accomplished by feeding a fat-enhanced diet, as will be discussed later. Early efforts to glycogen load horses as is done on humans were largely unsuccessful.

Fiber-type Recruitment:

Spares glucose and glycogen. Research suggests that intermediate muscle fiber types are recruited to become either Type I (slow twitch) fibers or Type IIA (fast-twitch oxidative) fibers, which utilize fat as an energy substrate much better than Type IIB (fast-twitch, glycolytic) fibers. This will reduce the production of lactic acid, as fat becomes the preferred energy substrate. This recruitment may depend upon the age of the horse and the type of conditioning (maximal or submaximal) used in the training program.

Enhances Waste Product Removal:

The horse's body appears to become much more efficient in clearing lactic acid from the muscles and CO2 from the blood over time.

Improves Waste Product Tolerance:

The horse can tolerate higher levels of lactic acid and CO₂ as he becomes more fit. The cumulative benefit of improved waste product removal and waste product tolerance is important to delaying fatigue.

LONG-TERM RESPONSE TO EXERCISE

Over many weeks of training, more permanent changes in physical and biochemical characteristics of the horse develop.

LONG-TERM RESPONSE OF BLOOD PARAMETERS TO EXERCISE

·         Increased packed cell volume (PCV) and increased blood volume.

·         Possible increase in peripheral O₂ utilization.

·         Increased work capacity at lower blood lactic acid concentration.

·         Increased tolerance of lactic acid.

·         Increased free-fatty acid utilization (sparing glucose).

LONG-TERM RESPONSE OF MUSCLE PARAMETERS TO EXERCISE:

·         Increased concentration of many enzymes used in energy metabolism.

·         Increased mitochondrial density.

·         Increased proportion of Type IIA fibers in locomotor muscles (may depend on age)

·         Increased capillary density.

·         Increased oxidative capacity (may depend on age).

·         Increased mobilization and utilization of free-fatty acids (especially in submaximal exercise).

·         Increased submaximal work capacity.

Physiological Changes due to Exercise

Natural response to training shifts from carbohydrate to fat as preferred energy source. Higher portion of workout/race run on fat. Increased glycogen stores in muscle. Increased time to production of lactic acid. Increased tolerance of lactic acid. 

Research on Dietary Fat and Exercise

Over (30) years of work has been done on exercise and feeding of fat in horses. Studies have been done in:

  a. Ponies

  b. Sprint race horses

  c. Endurance horses

  d. Cutting horses

  e. Dressage horses

  f. Hunter/Jumpers

Studies on Energy Sources:

Fat was suggested as preferred energy substrate for exercising horse with observations of decreased respiratory quotients during exercise and throughout training.  (Burke and Albert, 1978; Burke et al. 1979 & 1981)

High fat intakes (15% fat in grain portion) delayed lactate accumulation and delayed onset of fatigue. (Sloet et al., 2002)

High fat intakes (10% fat in grain portion) reduced reliance on CHO for energy, energy stores, preserved CHO stores, delayed fatigue. (Pagan et al., 2002)

                                                                     Study on Heat Production:

• Heat production was lowered in high fat (10%) diets (Kronfeld, et al., 2001)
• Heat reduced by 5%, water intake reduced by 12% (less need for evaporative cooling)
• Less heat = less water intake = less weight carried, helps improve performance

Studies on Muscle Glycogen Content:

Fat intake improved muscle glycogen levels; the effect peaked at 12% fat in diet.  (Hambleton, et al., 1980; Duren et al., 1990)

Studies on Muscle Disease:

High fat diets reduced tying-up by lowering CK levels (20% of DE as fat)

     (Valentine et al., 1998)

High fat feeding with low starch reduced CK levels and reduced tying-up (20% of DE as fat)         (McKenzie et al., 2002)

Study on the Effect on Behavior:

In horses, feeding fat reduced activity and excitability. In addition, fat reduces circulating levels of insulin and cortisol.

–     Less excitability

–     More acceptable behavior for horse owner

–     Performance improved by a better controlled, less excitable horse (Holland et al., 1996)

Study on Long-term feeding:

Long term feeding of fat did not influence any blood parameters, thus it is safe to feed for long periods. (Up to 16% fat in grain ration) (Zeyner et al., 2002)

Negative Effects of High Dietary Soluble CHO on Exercise

The main effects were are trying to reduce by minimizing the soluble CHO (sugar and starch) content of the equine athlete’s diet are lactic acid production (already discussed), as well as the insulin increase caused by increased blood glucose levels due to high soluble CHO diets.

The effects of high blood insulin levels due to sugar/starch digestion in the foregut are: 

Increased movement of glucose and amino acids into cells. This action may correlate to a horse tying-up).

Increased glycolysis. This may also correlate to tying-up by increasing lactic acid production.

Affects serotonin levels in brain. May explain hyperactivity and behavioral problems in some horses on high CHO diets.

Has been associated with ulcers

Research has suggested diets greater than 30% soluble CHO will bypass the small intestine and pass to the hindgut, where they will be fermented by the microbes.

The digestion of sugar/starch digestion in the hindgut favors lactic acid production, which is poorly absorbed and results in a reduction of pH in the hindgut. Acidic pH is correlated to:

•  Osmotic diarrhea (water shifts in to large intestine).
•  Overgrowth of pathogenic bacteria.
•  Lysis of beneficial bacteria.
•  Risk of endotoxemia and laminitis.
   
  

SUMMARY – How do we manage nutrition for the equine athlete?

• Supply up to 15-20% of needed calories with fat during training and events.
• Decrease starch in diet (less corn, molasses etc.).  Increase digestible fiber in diet (excellent quality grass hay, dried beet pulp).
• Control feed intake – feed more often during the day; make good grass hay available at all times.
• Use professionally designed diet.
• Supply electrolytes when horse is sweating.

References

Burke DJ, Albert WW. Methods for measuring physical condition and energy expenditure in horses. J Anim Sci. 1978 Jun;46(6):1666-72. 

Burke DJ, Albert WW.Comparative Training Effects of the Walker, Treadmill and Riding on Quarter Horse Mares. Proc. Sixth ENPS Symposium, April, 1979. 

Burke DJ, Albert WW. And Harrison PC.Effect of Training, Racing and Diet on Heart Rate, Respiratory Quotient, Energy  Expenditure Rate and Muscle Lactic Acid Production in Horses. Proc. Seventh ENPS Symposium, April, 1981. 

Hambleton PL, Slade LM, Hamar DW, Kienholz EW, Lewis LD. Dietary fat and exercise conditioning effect on metabolic parameters in the horse. J Anim Sci. 1980 Dec;51(6):1330-9. 

Hinchcliff, K.W., et al, 2004. Equine Sports Medicine and Surgery: Basic and Clinical Sciences of the Equine Athlete, Saunders, St. Louis, Mo. 

Hoffman RM, Boston RC, Stefanovski D, Kronfeld DS, Harris PA.  Obesity and diet affect glucose dynamics and insulin sensitivity in Thoroughbred geldings.J Anim Sci. 2003 Sep;81(9):2333-42. 

Kronfeld DS. Dietary fat affects heat production and other variables of equine performance, under hot and humid conditions. Equine Vet J Suppl. 1996 Jul;(22):24-34. 

McKenzie EC, Valberg SJ, Godden SM, Pagan JD, MacLeay JM, Geor RJ, Carlson GP.  Effect of dietary starch, fat, and bicarbonate content on exercise responses and serum creatine kinase activity in equine recurrent exertional rhabdomyolysis. J Vet Intern Med. 2003 Sep-Oct;17(5):693-701. 

Pagan JD, Geor RJ, Harris PA, Hoekstra K, Gardner S, Hudson C, Prince A.  Effects of fat adaptation on glucose kinetics and substrate oxidation during low-intensity exercise.

Equine Vet J Suppl. 2002 Sep;(34):33-8. 

Potter GD, Hughes SL, Julen TR, et al. A review of research on digestion and utilization of fat by the equine. Pferdeheilkunde 1992; 1:119-123. 

Sloet van Oldruitenborgh-Oosterbaan MM, Annee MP, Verdegaal EJ, Lemmens AG, Beynen AC.  Exercise- and metabolism-associated blood variables in Standardbreds fed either a low- or a high-fat diet.

Equine Vet J Suppl. 2002 Sep;(34):29-32.  

Valentine BA, Hintz HF, Freels KM, Reynolds AJ, Thompson KN. Dietary control of exertional rhabdomyolysis in horses. J Am Vet Med Assoc. 1998 May 15;212(10):1588-93. 

Zeyner A, Bessert J, Gropp JM. Effect of feeding exercised horses on high-starch or high-fat diets for 390 days. Equine Vet J Suppl. 2002 Sep;(34):50-7.        

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