[Levels of thyroxine, beta carotene and vitamin A during successful and unsuccessful insemination of heifers].

We studied the concentrations of thyroxine (T4), beta-carotene and vitamin A (vit. A) on the day (zero-th day) of the first successful and unsuccessful insemination of 63 heifers that were administered feed rations balanced according to the Czechoslovak standard CSN 46,7070, housed all the year round, inseminated at uniform time (8:00-9:00 a. m.) and with blood samplings at uniform time (10:00-12:00 a. m.). In the repeat-breeder heifers during the first insemination the above parameters were determined in the same conditions on the day of their second, or third successful and also unsuccessful insemination; the changes relevant to the first insemination were evaluated. In relation to the day of the first successful insemination, we recorded a significant increase in T4 concentration (P less than 0.001; P less than 0.001) on the day of the second, or third successful inseminations. During the second insemination we recorded significantly lower T4 concentrations in the cows which had failed to be inseminated in comparison with successfully inseminated cows; these concentrations did not differ significantly from T4 concentrations in the heifers that failed to become pregnant in the first insemination. Parallelly with the rise in T4 concentration, beta-carotene concentrations also increased during the second and third inseminations (P greater than 0.05). No difference was recorded in beta-carotene concentrations after the first and second unsuccessful inseminations.(ABSTRACT TRUNCATED AT 250 WORDS)