The Relationship of Serum Thyroxine Level to Body Mass of Piglets during Their Postnatal Development

Abstract

Dvorak M., M. Neumannova and J. Bursa: The Relationship of Serum Thyroxine Level to Body Mass of Piglets during Their Postnatal Development. Acta vet., Brno, 55, 1986: 11-21. Total thyroxine (T4) levels were determined repeatedly in piglets from birth to 74 days of age in five experiments using 115 piglets from 13 litters divided into groups of heavier and lighter animals according to their body mass at weaning at 21 or 28 days of age and, in one of the experiments, into a group of normally growing piglets and a group of piglets with retar-ded growth in consequence of sideropoenic anaemia. The thyroxinaemia of newborn piglets was twice that found in adult pigs and continued at a high level, with some variation, throughout the suckling period. By 3 weeks after weaning it had decreased but still exceeded that found in 6-month-old feeder pigs. The decrease was small in piglets with good growth performance after weaning. In groups of newborn piglets, older piglets and feeder pigs of lighter body mass, T4 concentration values were generally lower than in their heavier counterparts of equal ages, although the differences did not reach significance. It is suggested that the. decisive criterion of body growth in assessing its direct relationship to T4 level is relative gain in body mass, a parameter presumably corresponding to the level of nutrition. Low thyroxinaemia was found in piglets with poor or no body mass gain in the last days. This hypothyreous state seems to be a secondary phenomenon and may be transient. Thyroid gland. hormones. body growth. nutrition. anaemia of piglets. swine.Endocrine glands involved in body growth regulation, interactions between nutrition and hormones as well as hormone control of protein genesis have been recently receiving increased attention also in relation to animal production (Dauzier 1980;Galbraith and Topps 1981;Trenkle and Marple 1983;Buttery 1983). The investigations to date have indicated the complexity of the problem and yielded conflicting results for individual animal species.. An important role among endocrine regulators is played by hormones of the thyroid gland. Thyroxine (T4) and triiodothyronine (Ta) are generally regarded as essential for normal growth, its differentiation in organisms and for maturation of the skeleton. Their numerous control effects affect metabolism, particularly energy metabolism and calorigenesis. The variety of effects observed at different levels of these hormones and the relatively long latent period before their consequences become apparent make it difficult to understand the mechanisms involved in their action and to distinguish the effects .conditioned directly by their presence from those bringing other regulators into operation, e.g. growth hormone (Menezes-Ferreira and Torresani 1983). In young rats, growth hormone is more effective in promoting the growth of body mass than that of the skeleton, whereas with T4 the reverse is the case. The two hormones act synergistically in bringing the growth of hypophysectomized infant rat...