Objective—To evaluate effects of fats with odd and even numbers of carbon atoms on muscle metabolism in exercising horses with polysaccharide storage myopathy (PSSM).
Animals—8 horses with PSSM (6 females and 2 males; mean ± SD age, 6.3 ± 3.9 years).
Procedures—Isocaloric diets (grain, triheptanoin, corn oil, and high-fat, low-starch [HFLS] feed) were fed for 3 weeks each; horses performed daily treadmill exercise. Grain was fed to establish an exercise target, and HFLS feed was fed as a negative control diet. Daily plasma samples were obtained. For each diet, a 15-minute exercise test was performed, and gluteus medius muscle specimens and blood samples were obtained before and after exercise.
Results—Feeding triheptanoin, compared with the corn oil diet, resulted in exercise intolerance; higher plasma creatine kinase (CK) activity and concentrations of C3:0- and C7:0-acylcarnitine and insulin; and lower concentrations of nonesterified fatty acids (NEFA) and C16:0-, C18:1-, and C18:2-acylcarnitine, without changes in concentrations of plasma glucose or resting muscle substrates and metabolites. Feeding grain induced higher CK activity and insulin concentrations and lower NEFA concentrations than did corn oil or HFLS feed. Feeding grain induced higher glucose concentrations than did triheptanoin and corn oil. In muscle, feeding grain resulted in lower glucose-6-phosphate, higher citrate, and higher postexercise lactate concentrations than did the other diets.
Conclusions and Clinical Relevance—Triheptanoin had detrimental effects, reflecting decreased availability of NEFA, increased insulin stimulation of glycogen synthesis, and potential inhibition of lipid oxidation. Long-chain fats are the best dietetic for PSSM.
Objective—To compare effects of corn oil or a 7-carbon fat (triheptanoin) on acylcarnitine, lipid, and carbohydrate metabolism in plasma or muscle of exercising horses.
Animals—8 Thoroughbred geldings.
Procedures—Horses received isocaloric diets containing 650 mL of oil (triheptanoin or corn oil)/d for 18 or 25 days in a crossover design with a 26-day washout period. On day 17 or 24 of each feeding period, the respective oil (217 mL) was nasogastrically administered; 120 minutes later, horses performed a 90-minute submaximal exercise test (SET). Blood and muscle samples were obtained before oil administration and immediately before (blood only), during (blood only), immediately after, and 24 hours after SETs.
Results—Compared with values before oil administration, triheptanoin administration increased plasma insulin and C7:0-, C5:0- and C3:0-acylcarnitine concentrations, whereas corn oil administration increased plasma NEFA concentrations. During SETs, plasma C7:0-, C5:0-, and C3:0-acylcarnitine concentrations were higher when triheptanoin, rather than corn oil, was administered to horses. Plasma glucose, NEFA, and C2:0-, C18:1-, and C18:2-acylcarnitine concentrations increased during SETs similarly for both oils. Respiratory quotient and muscle lactate, citrate, malate, glycogen, and ATP concentrations changed similarly from before to after SETs for both oils. Compared with muscle concentrations immediately after SETs, those for glucose-6-phosphate and citrate 24 hours after SETs were lower and for glycogen were similar to values before SETs.
Conclusions and Clinical Relevance—Fatigue was not associated with depletion of citric acid cycle intermediates for either oil. Triheptanoin induced a significantly higher insulin secretion and did not appear to enhance muscle glycogen repletion.
Objective—To determine daily variation in urinary
clearance and fractional excretion (FE) of electrolytes
and minerals within and between horses and to compare
volumetric and single-sample urine collection for
determining FE values of diets with a range of dietary
cation-anion balance (DCAB).
Animals—5 Thoroughbred and 6 mixed-breed mares.
Procedure—3 isocaloric diets with low, medium, and
high DCAB values (85, 190, and 380 mEq/kg of dry
matter, respectively) were each fed for 14 days. Daily
blood samples, single urine samples collected by
using a urinary catheter (5 mares), and volumetric
urine collections (6 mares) were obtained during the
last 72 hours of each diet.
Results—Urine and plasma pH values, plasma concentrations,
and FE values of sodium, chloride, potassium,
magnesium, phosphorus, and calcium were
altered by varying the DCAB. Noticeable variation in
clearance and FE values was detected within horses
from day-to-day on the same diet as well as between
horses. Fractional excretion values were not significantly
different between single-sample and volumetric
methods, except for magnesium in the high DCAB
diet. Volumetric and single-sample collections
revealed similar patterns of change in urinary FE values
with varying DCAB, except for calcium and magnesium.
Conclusions and Clinical Relevance—Substantial
variation in clearance and FE of electrolytes and minerals
are evident within horses between 24-hour periods
as well as between horses fed a specific diet.
Three daily urine samples provide similar information
regarding dietary-induced changes in clearance and
FE values (excluding calcium and magnesium) as that
obtained by volumetric urine collection. (Am J Vet Res 2003;64:284–291)
Objective—To determine whether plasma, urine,
and fecal electrolyte and mineral concentrations differ
between clinically normal horses and
Thoroughbreds with recurrent exertional rhabdomyolysis
(RER) after consumption of diets varying in
Animals—5 Thoroughbred mares with RER and 6
clinically normal mixed-breed mares.
Procedure—Each of 3 isocaloric diets designated as
low, medium, and high on the basis of dietary cationanion
balance (DCAB) values of 85, 190, and 380,
respectively, were fed to horses for 14 days. During
the last 72 hours, 3 horses with RER and 3 control
horses had daily urine and fecal samples obtained by
total 24-hour collection. Remaining horses had urine
samples collected daily by single catheterization.
Results—For each diet, no differences existed
between horses with RER and control horses in plasma
pH, electrolyte concentrations, and creatine
kinase activity or in urine pH and renal fractional
excretion (FE) values. Plasma pH, strong ion difference,
bicarbonate and total carbon dioxide concentrations,
and base excess decreased and plasma chloride
and ionized calcium concentrations increased
with decreasing DCAB. Urine pH decreased with
decreasing DCAB. The FE of chloride and phosphorus
were greatest for horses fed the low diet. The FE values
for all electrolytes exept magnesium did not differ
between urine samples obtained by single catheterization
and total 24-hour collection. Daily balance of
calcium, phosphorus, sodium, chloride, and potassium
did not differ significantly among horses fed the
Conclusions—In clinically normal horses and in horses
with RER, the DCAB strongly affects plasma and
urine pH and the FE of sodium, potassium, chloride,
and phosphorus. (Am J Vet Res 2002;63:1053–1060)