Thyroxine in Blood Plasma Related to Plasma Levels of Acetoacetate and Glucose in Ketotic and Healthy Cows

Brief Research Report: Effect of Triiodothyronine on Hepatic Growth Hormone Receptor Expression in Primary Bovine Hepatocytes

In previous studies, triiodothyronine (T3) was found to be lower in cows with ketosis and an effect of T3 on Growth Hormone Receptor (GHR) expression is described, e. g., in a human hepatoma cell line. Therefore, this study aimed to test whether T3 affects GHR messenger RNA (mRNA) expression in a well-established bovine hepatocyte model. Hepatocytes were kept in a sandwich culture and stimulated for 6 days with constant (10 μg/ml) or decreasing (from 10 to 5 μg/ml) T3 concentrations, and GHR, as well as IGF-1 mRNA expression, was measured using real-time polymerase chain reaction (RT-PCR). We could confirm in vitro that T3 has a stimulatory effect on GHR1A mRNA expression.

Thyroid hormone profiles and TSH evaluation during early pregnancy and the transition period in dairy cows

The thyroid hormone axis is one important endocrine system within a complex system of various factors and hormones necessary to establish and maintain pregnancy in cattle and in metabolic adaptations towards lactation. Pregnancy and lactation occur contemporaneously in dairy cows, and have major impacts on thyroid hormones as well as status of the hypothalamus-pituitary thyroid axis influences pregnancy and lactation. As especially the thyroid hormone axis with special focus to TSH is not well studies in the past, the aim of the study was to examine the thyroid hormone axis, especially in heifers during adaptation to the first lactation, to verify the association between lactation and thyroid hormones. Secondly, the early pregnancy period was the focus of the present investigation. To determine thyroid hormone patterns and especially thyroid-stimulating hormone (TSH) during the transition period, 12 primiparous Holstein Friesian cows and 41 pregnant and 34 non-pregnant pluriparous cows were sampled. During the transition period, thyroxin (T₄) concentrations decreased after calving in primiparous cows, and the milk yield [kg] was negatively correlated with triiodothyronine (T₃) and T₄ concentrations. In pregnant and non-pregnant pluriparous cows, T₃, T₄, TSH and free T₄ (fT₄) decreased between the day of ovulation (day 0) and day 18. From day 18 of gestation to day 100 after AI, an increase in TSH and fT₄ and a decrease in Reverse T₃ (rT₃) was observed in the pregnant cows. In conclusion, the results of the present study confirm that regulative processes within the thyroid hormone metabolism occur during early lactation. For the first time it could be shown in dairy cows that TSH and fT4 increased during early pregnancy whereas rT3 decreased indicating also in bovine species a TSH stimulatory effect by pregnancy.

Prefeeding plasma acetoacetate and glucose in healthy, lactating heifers. Variations related to milk yield, metabolic balances and stage of lactation

When measured before morning feeding plasma acetoacetate (ACAC) increased and glucose (GL) decreased significantly with increasing milk yield (fat corrected, FCM) within 2 groups of half-sister related heifers which did not suffer from clinical ketosis. The groups received respectively A: 7 kg and B: 4 kg/d of concentrates in addition to grass silage ad libitum (each group 88 animals). Correlation coefficients of the same magnitude between the 3 variables mentioned were obtained in the 1st and 3rd month of lactation in spite of a narrowing of the ACAC range from 0.024-0.66 to 0.019-0.16 mmol/l. Reproducibility of differences between animals in milk yield and in the plasma components was evidenced by significant correlations between measurements in the 1st and 3rd month. The B-animals produced 2.4 kg/d less FCM than the better fed A group (A, 1st month of lactation 19.8 +/- 3.1 kg/d) while the mean values for ACAC and GL remained practically unaffected by the difference in feeding. B cows gave consistently 5-6% lower GL means (p < 0.01) than A animals with identical yields. Animals which showed marked ACAC increment during the first 5-6 weeks of lactation produced 3-4 kg more FCM/d than equally fed animals with constantly low ACAC levels. The estimated energy deficit of this ketonaemic, high-producing category corresponded to the production of 4.5-6 kg FCM/d from body reserves. Low ACAC values (< 0.05 mmol/l) were reproduced with a standard deviation of +/- 4% with the automated nitroprusside method described.

Prefeeding plasma acetoacetate and glucose in healthy, lactating heifers. Variations related to milk yield, metabolic balances and stage of lactation

When measured before morning feeding plasma acetoacetate (ACAC) increased and glucose (GL) decreased significantly with increasing milk yield (fat corrected, FCM) within 2 groups of half-sister related heifers which did not suffer from clinical ketosis. The groups received respectively A: 7 kg and B: 4 kg/d of concentrates in addition to grass silage ad libitum (each group 88 animals). Correlation coefficients of the same magnitude between the 3 variables mentioned were obtained in the 1st and 3rd month of lactation in spite of a narrowing of the ACAC range from 0.024-0.66 to 0.019-0.16 mmol/l. Reproducibility of differences between animals in milk yield and in the plasma components was evidenced by significant correlations between measurements in the 1st and 3rd month. The B-animals produced 2.4 kg/d less FCM than the better fed A group (A, 1st month of lactation 19.8 +/- 3.1 kg/d) while the mean values for ACAC and GL remained practically unaffected by the difference in feeding. B cows gave consistently 5-6% lower GL means (p < 0.01) than A animals with identical yields. Animals which showed marked ACAC increment during the first 5-6 weeks of lactation produced 3-4 kg more FCM/d than equally fed animals with constantly low ACAC levels. The estimated energy deficit of this ketonaemic, high-producing category corresponded to the production of 4.5-6 kg FCM/d from body reserves. Low ACAC values (< 0.05 mmol/l) were reproduced with a standard deviation of +/- 4% with the automated nitroprusside method described.