Development of diurnal rhythm in some metabolic parameters in foals

Total and free iodothyronine levels of growing Thoroughbred foals: Effects of weaning and gender

“…The results obtained confirm the presence of high concentrations of circulating T 3 and T 4 hormones in foals, previously reported in the perinatal period in the newborn foal (Irvine and Evans, 1975;Silver et al, 1991;Murray and Luba, 1993), in neonatal foals aged 1.5 to 4 mo (Chen and Riley, 1981), during the first 6 mo of life (Komosa et al, 1990) and in foal aged 1 to 9 mo (Malinowski et al, 1996). High serum T 3 and fT 3 concentrations in the first 3 mo of age and very high T 4 and fT 4 levels in the first 6 mo of life appear to have significant and differentiated roles as metabolic hormones for the development and differentiation of young growing foals.…”

“…No differences in plasma T 3 and T 4 concentrations in weanling horses fed restricted diets were reported (Glade et al, 1984;Glade and Reimers, 1985), whereas in other species, reduced intakes decreased thyroid hormone concentrations (Ellenberger et al, 1989;Buonomo and Baile, 1991;Janan et al, 1995). In addition, the development of diurnal rhythms of thyroid hormones was observed in foals from birth till the end of the first year of their life (Komosa et al, 1990), but the environmental conditions and physiological state of an organism may modify the course and amplitude of rhythms. Postnatal changes in total and free iodothyronine concentrations of foals and their correlations with physiological conditions have been investigated (Irvine and Evans, 1975;Chen and Riley, 1981), but their correlations with growing and weaning are not evaluated in detail.…”

Changes of circulating β-endorphin, adrenocorticotrophin and cortisol concentrations during growth and rearing in Thoroughbred foals

“…In addition, diurnal cortisol rhythms were found to already occur in the first 2 months of foal life, with the acrophase at 08:30 a.m. (Komosa et al, 1990) and at 3, 7 and 11 weeks of foal life (Flisińska-Bojanowska et al, 1989). A circadian cortisol rhythm exists in horses in the absence of any known cues imposed by humans.…”

Circadian pattern of hepatosomatic index, liver glycogen and lipid content, plasma non-esterified fatty acid, glucose, T3, T4, growth hormone and cortisol concentrations in Oncorhynchus mykiss held under different photoperiod regimes and fed using demand-feeders

“…However, it is possible that both photoperiod-and feedingentrained rhythms are be present, one superimposed on the other. This appears to be the case in some mammals in which postprandial increases in plasma cortisol levels (Follenius et al 1982;Shiraishi et al 1984) are overlaid on a circadian rhythm of plasma cortisol concentration in which highest levels precede the onset of feeding activity (Honma et al 1983Saito et al 1989;Komosa et al 1990). …”