Effects of pregnancy and lactation on plasma lipid and lipoprotein concentrations, lipoprotein composition and post-heparin lipase activities in Shetland pony mares.

This study investigates how pregnancy and lactation might influence various aspects of blood lipid metabolism in Shetland pony mares, with a specific focus on their connection to elevated blood fat (hyperlipaemia), a condition more common in late pregnancy and early lactation. The researchers noticed significant changes in the amounts and composition of certain lipoproteins in the ponies’ blood, shedding light on possible metabolic origins for hyperlipaemia during these stages.

Study Design and Results

• The researchers took blood samples from six healthy Shetland pony mares at three different stages: before pregnancy, in the final six weeks of gestation, and one month after birth.
• They measured the concentrations of various types of lipids and lipoproteins in the blood, testing the hypothesis that pregnancy and lactation lead to changes stimulating hyperlipaemia.
• In pregnant ponies, levels of cholesterol and triglycerides were significantly increased. This rise was linked to increased quantities of high-density lipoproteins (HDL) and very low-density lipoproteins (VLDL), both responsible for transporting fats around the body.
• The increased amount of VLDL was enriched with triglyceride but had less protein, indicating heightened production of triglyceride in the liver and increased VLDL secretion. This alteration occurred without any uptick in lipoprotein lipase or hepatic lipase activities, enzymes typically leading to the breakdown of VLDL.

Post-birth Observations

• After giving birth, the ponies experienced a significant drop in triglycerides and VLDL levels, attributed to the increased activity of lipoprotein lipase, sparking speculation about the enzyme’s likely induction in mammary tissue for milk fat synthesis.
• Despite the decrease in triglycerides and VLDL, cholesterol levels stayed high, and non-esterified fatty acid concentrations significantly increased.
• VLDL still exhibited high triglyceride enrichment but with normal cholesterol and protein compositions, although the amount of phospholipids was lessened.

Connections to Hyperlipaemia and Conclusions

• The changes observed in pregnant ponies’ VLDL concentrations and compositions were similar to previously reported alterations in ponies with hyperlipaemia.
• These findings suggest a plausible metabolic basis for the incidence of hyperlipaemia during late gestation, providing direction for future investigations into mitigating the health concerns arising from this condition in ponies.