2,4-Thiazolidinedione in Well-Fed Lactating Dairy Goats: I. Effect on Adiposity and Milk Fat Synthesis
Background: In a previous study, treatment of goats with the potential PPARγ agonist 2,4-thiazolidinedione (2,4-TZD) did not affect milk fat content or the expression of milk-fat related genes. This lack of response was attributed to potential vitamin A deficiency and/or poor body condition of the animals. In the present study, we aimed to test the hypothesis that PPARγ activation influences milk fat synthesis in goats with optimal body condition and adequate vitamin A levels.
Methods: Lactating goats, fed a diet meeting NRC requirements and supplemented with adequate vitamin A, were administered daily injections of 8 mg/kg BW of 2,4-TZD (n = 6) or saline (n = 6, control) for 26 days. Blood metabolic profiles, milk yield, milk components, and fatty acid profiles were measured. Gene expression related to glucose and lipid metabolism was assessed in both adipose tissue and mammary epithelial cells (MEC). The size of adipocytes was evaluated using histological analysis.
Results: Compared to the control group, plasma concentrations of NEFA, MF-438, and available fatty acids decreased, while glucose levels increased in the 2,4-TZD group. In adipose tissue, adipocyte size was larger, and the expression of genes associated with insulin signaling and glucose metabolism was upregulated in the 2,4-TZD group. In MEC, however, the expression of SCD1 and the desaturation of stearate were lower in the 2,4-TZD group compared to the control.
Conclusions: The results suggest that 2,4-TZD did not activate PPARγ as expected, and there was no effect on milk fat synthesis, despite a significant anti-lipolytic effect on adipose tissue.