Blood values of thyroxine and triiodothyronine in grazing Friesian cows

Abstract

In order to establish the plasma thyroid hormones concentrations in grazing Frisian cows, 110 blood samples were analysed for tri-iodothyronine (T3) and thyroxine (T4). Samples were selected from dairy herds that requested the university's metabolic profile service and were restricted to those which presented no abnormalities in blood composition.

Blood samples were obtained from early lactation (n=55) and late pregnancy (n=55) cows. Plasma values of T3 and T4 were determined by radioimmunoassay technique using the commercial kit Coat-A-Count total T3 and Coat-A-Count total T4 for T3 and T4 respectively. Significance among the means of different groups were determined using the Student's t test (p<0.05), with a 95% confidence interval.

The mean (±S.D.) plasma T3 value was 1.40±0.43 nmol/L, similar to those in the literature. Lactating cows had higher T3 values (1.54±0.43 nmol/L) than late pregnancy cows (1.25±0.37 nmol/L) (p<0.05). T4 values (mean±S.D.) were 41.0±11.6 nmol/L, with no differences between lactating and pregnant cows. These values were lower than the reference values given in the literature.

It is concluded that it is possible to measure T3 and T4 in cows using the RIA technique and the values obtained can be used as reference values. Allowance for differences due to physiological condition, may have to be made.