Thyroid hormones and their correlations with serum glucose, beta hydroxybutyrate, nonesterified fatty acids, cholesterol, and lipoproteins of high-yielding dairy cows at different stages of lactation cycle
摘要
The relationships between circulating thyroid hormones and serum glucose, beta hydroxybutyrate (BHB), nonesterified fatty acid (NEFA), cholesterol and lipoproteins of high-yielding dairy cows were studied in 125 adult Holsteins at various stages of lactation cycle: early (far-off) dry period (n = 24), late (close-up) dry period (n = 10), fresh cows (n = 22), early lactation (n = 13), mid-lactation (n = 27) and late lactation (n = 29). Decreased levels of thyroxin (T4) and triiodothyronine (T3) were noted in peripartum cows which were extended to mid- and late-lactation cows, respectively. In fresh cows, glucose showed correlations with T4 (r = 0.619, P < 0.01) and T3 (r = 0.627, P < 0.01). In the same cows there were correlations between T4 and BHB (r = 0.590, P < 0.01) and NEFA (r = 0.470, P < 0.01). In late dry cows, free thyroxin (fT4) showed correlations with triglyceride (TG) and very-low-density lipoprotein (VLDL; r = −0.638, P < 0.05). Pooled data of the various stages of lactation cycle revealed correlations between glucose and T4 (r = 0.20, P < 0.05), glucose and T3 (r = 0.395, P < 0.01), cholesterol and T3 (r = −0.201, P < 0.05), and free triiodothyronine (fT3) and high-density lipoprotein (HDL; r = 0.178, P < 0.05). It appears that the time and the pattern of changes and/or correlations of serum thyroid hormones and lipid fractions may vary among dairy cows and other animals.