Abstract
AbstractThe hormonal activity of the thyroid gland has an important role in ruminants for the modulation of metabolic variables. In this study changes in thyroid hormones and biochemical parameters in dairy cows around calving were evaluated and the critical thyroid hormones thresholds for predicting the risk of ketosis were estimated. Blood samples were collected from 82 dairy cows at 5±3 days pre-partum and 5±3 days postpartum. Serum values of triiodothyronine (T3), thyroxine (T4), thyroid-stimulating hormone (TSH), non-esterified fatty acids (NEFA), β-hydroxybutyrate (BHB), insulin, glucose, Ca, Cl, Mg, P, K, Na, aspartate transaminase (AST), alanine transaminase (ALT) and urea were evaluated. Signifi cant decrease in the levels of T3, T4 and TSH was found in the postpartum period. The values of T3 and T4 were negatively correlated with NEFA and BHB levels, and TSH values were negatively correlated with NEFA. A critical T3 threshold was found by means of ROC analysis for predicting the risk of ketosis. T3 values < 1.23 nmol/L were associated with BHB > 1.10 mmol/L in postpartum, which represents the BHB threshold commonly used as the indicator of hyperketonaemia. The results confirm that the peripartum period is accompanied by marked changes in circulating thyroid hormone profile that is correlated with lipomobilization predictors.
Highlights
Transition dairy cows are often characterized by a decrease in serum glucose level and an increase of nonesterified fatty acids (NEFA) and β-hydroxybutyrate (BHB) serum concentrations, suggesting the difficulty of dairy cows to cope with the energy demand which characterizes the transition period [7]
Statistical analysis showed lower values for T3 (P < 0.01), thyroid-stimulating hormone (TSH) (P < 0.05), T4 (P < 0.001), insulin (P < 0.01), glucose (P < 0.01), alanine transaminase (ALT) (P < 0.001) and urea (P < 0.05) in post-partum than in pre-partum; whereas, higher BHB and NEFA values were found at post-partum than at pre-partum (P < 0.01)
The results obtained in the present study highlight the effect of the transition period on serum thyroid hormones, BHB, NEFA, glucose, insulin, aspartate transaminase (AST), ALT, urea and K concentration in dairy cows
Summary
The time from late pregnancy to early lactation is known as the transition period and it is recognized as the period between 3 weeks before to 3 weeks after parturition in the ruminant [1,2,3].Fiore et al.: Changes in thyroid hormones levels and metabolism in dairy cows around calvingCows in late gestation have higher metabolic demands and less feed intake compared to cows in the early dry period and enter a period of negative energy balance (NEB) intensified in early lactation when feed intake lags behind milk production [4,5].Thyroid gland hormonal activity has an important role in the peripartal period for determining the cell metabolism intensity, the metabolism of lipids and carbohydrates, as well as the course of lactation. Fiore et al.: Changes in thyroid hormones levels and metabolism in dairy cows around calving. Conversion of T4 in peripheral tissues produces the active hormone 3,5,3’-tri-iodothyronine (T3) and reverse T3 (rT3) which is thought to be metabolically inactive Both T3 and T4 are present in the blood circulation, the physiological effects are attributed almost only to T3 [15,16,17]. In view of such considerations, the aim of the present study was to evaluate the changes of some biochemical parameters and of serum thyroid hormones including T3, T4 and TSH, as well as their relationship in dairy cows around calving. The critical thyroid hormones thresholds based on the critical values of BHB and NEFA, previously identified as predictors of ketosis, were estimated in order to identify possibly diseased dairy cows
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