Lipoprotein cholesterol and progesterone secretion in cycling pony mares fed a control or a fat-supplemented diet

Abstract

The objective of this study was to quantify concentrations of serum progesterone, total cholesterol (TC), and lipoprotein-cholesterol fractions (HDL, LDL, and VLDL) in cycling pony mares fed a conventional versus a 12% fat-supplemented (animal fat) diet. Six mature pony mares were used in a switchback model so each mare acted as its own control. To diminish period effects, half of the mares began the study on the control diet and half on the fat-supplemented diet. Test cycles consisted of an entire estrous cycle during which blood samples were collected during the interovulatory period via the jugular vein. Blood was collected on D 0 and every other day therafter for progesterone analysis which was determined by a commercial solid phase 1251 radioimmunoassay kit. Blood was collected on D 0 and every 7 d thereafter for lipoprotein and TC analysis. Lipoproteins were separated on a polyacrylamide gel by electrophoresis and TC was determined enzymatically. Overall plasma TC, HDL-cholesterol, and VLDL-cholesterol concentrations were significantly (P < .05) effected by diet with mares exhibiting higher concentrations while on the fat-supplemented diet at certain specific time periods. In general LDL-cholesterol concentrations were not affected by diet, but diet significantly affected (P < .05) one mare's LDL-concentrations. No diet effect was observed on progesterone; however, values tended to be higher in 4 of the 6 mares while on the fat-supplemented diet. A wide variation between individual mares was observed which led to mare having a highly signifcant effect (P <. 0 1) on HDL-and VLDL-cholesterol concentrations. Furthermore at least one mare was significantly affected by diet in each of the parameters studied, except progesterone. Data in this research indicate fat supplementation in pony mares leads to increased serum cholesterol, HDL-cholesterol, and VLDL-cholesterol, and that effects are highly dependent on individual mares.