Hyperlipemia in Horses: Effects of Undernutrition and Disease

SUMMARY Lipid mobilization was followed in a study of healthy horses in which food but not water was withheld for 120 hours. The rise in serum lipids was consistent with an initial release of free fatty acids and glycerol from adipose tissue. This was followed by a rise in serum triglyceride as the liver took up free fatty acids and converted them to triglycerides. Changes in total lipids reflected increases in individual serum lipid constituents, especially triglycerides which underwent the greatest absolute increase during food deprivation. The concentration of many serum lipids increased until a new steady state was reached, presumably the point at which increased production was balanced by removal. Numerical values for free fatty acids were 1.61 ± 1.84 (mean ± sd) and 27.78 ± 8.24 mg/dl in fed and food-deprived horses at plateau, respectively; triglyceride values were 31.12 ± 6.86 and 194.7 ± 79.5 mg/dl, respectively. Observations of healthy horses showed that serum triglyceride concentration rose to a variable extent and with a delay of at least 40 hours after food deprivation. Studies of sick horses confirmed that hypertriglyceridemia was associated with hypophagia, but that the converse was not always true. Thus hypophagia may exist without concomitant hypertriglyceridemia, but the presence of hypertriglyceridemia was a sound indicator of pre-existing hypophagia. A few sick horses had hyperlipemia. These had very high serum lipid concentrations (up to 3,000 mg of triglyceride/dl), cloudy serum, and fatty infiltration of the liver. There was a statistically significant, Ρ < 0.001, association between serum creatinine and triglyceride concentrations. We postulated that a metabolic block in the removal of triglyceride from serum existed in azotemic horses and that this exacerbated the effect of hypophagia on serum lipid concentrations.