Effects of hypothyroidism and withholding of feed on plasma lipid concentrations, concentration and composition of very-low-density lipoprotein, and plasma lipase activity in horses.

The study looks at the effects of hypothyroidism and withholding feed on certain concentrations of blood lipids and lipase activities in horses, particularly during a period of 96 hours. Findings suggest that hypothyroidism doesn’t significantly change how blood lipids respond to the lack of feed. It also appears that hypothyroidism doesn’t increase the likelihood of a horse developing hyperlipemia.

Study Methodology

• The study was conducted on two groups of adult mares: four healthy (euthyroid) mares and four that had thyroidectomy (making them hypothyroid).
• The horses were deprived of feed for 96 hours and blood samples were collected every 24 hours within this period.
• The blood samples were analyzed to determine concentrations of non-esterified fatty acid (NEFA), triglyceride (TG), total cholesterol (TC), and very-low-density lipoprotein (VLDL), as well as the composition of VLDL.
• Plasma lipase activities were measured after the 96-hour feed withdrawal period and again 12 days after resumption of feeding.

Results

• Under the conditions of feed deprivation, blood concentrations of NEFA, VLDL, TG, and TC changed significantly over time in both groups of horses.
• NEFA and VLDL concentrations increased 10-fold and 5-fold and 9-fold respectively in euthyroid and hypothyroid horses within the 96 hours.
• TG concentrations rose 8-fold in both groups, while TC concentrations went up by 33% and 30% respectively.
• The composition of VLDL was particularly affected in the euthyroid horses after the feed deprivation.
• Both lipoprotein lipase and hepatic lipase activities were higher in horses that were deprived of feed, but the activity of hepatic lipase was significantly lower in hypothyroid horses.

Conclusions

• Hypothyroidism didn’t significantly alter how blood lipids response to feed deprivation.
• Thyroid hormones appear to reduce variability in blood lipid concentrations but doesn’t determine susceptibility to hyperlipemia.
• The study suggests that hypothyroidism is not a factor in the development of hyperlipemia (high amount of fat in the blood) in horses.