Thyroid hormones correlate with field metabolic rate in ponies, Equus ferus caballus.
During winter, free-living herbivores are often exposed to reduced energy supply at the same time that energy needs for thermoregulation increase. Several wild herbivores as well as robust horse breeds reduce their metabolism during times of low ambient temperature and food shortage. Thyroid hormones (THs) affect metabolic intensity and a positive effect of THs on basal metabolic rate (BMR) has been demonstrated in mammals and birds. As BMR and field metabolic rate (FMR) are often assumed to be intrinsically linked, THs may represent a reliable indicator for FMR. To test this hypothesis, 10 Shetland pony mares were kept under semi-extensive central European conditions. During the winter season, one group was fed 60% and one group 100% of their maintenance energy requirements. We measured FMR, locomotor activity, resting heart rate and TH levels in summer and winter. FMR, locomotor activity, resting heart rate and total T3 concentrations decreased substantially in winter compared with summer, whereas total T4 increased. Food restriction led to a reduced FMR and resting heart rate, while THs and locomotor activity were not affected. Across both seasons, FMR, resting heart rate and locomotor activity were positively correlated with total T3 but negatively and more weakly correlated with total T4.
Department of Animal Sciences, University of Göttingen, Göttingen 37075, Germany.
Lea
L
Brinkmann
Department of Animal Sciences, University of Göttingen, Göttingen 37075, Germany.
Martina
M
Gerken
Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK.
Catherine
C
Hambly
Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK Institute of Genetics and Developmental Biology, State Key Laboratory of Molecular Developmental Biology, Chinese Academy of Sciences, Beijing 100101, PR China.
John R
JR
Speakman
Department of Animal Sciences, University of Göttingen, Göttingen 37075, Germany ariek@uni-goettingen.de.
Alexander
0000-0002-1045-6904
A
Riek
D000818:Animals; D001481:Basal Metabolism / Q000502:physiology*; D001835:Body Weight; D004734:Energy Metabolism / Q000502:physiology; D005060:Europe; D005260:Female; D006736:Horses / Q000378:metabolism*; D008124:Locomotion / Q000502:physiology; D012146:Rest / Q000502:physiology; D012621:Seasons; D013963:Thyroid Hormones / Q000378:metabolism*
D013963:Thyroid Hormones
Energy expenditure; Food restriction; Horses; Locomotor activity; Resting heart rate; Thyroxine; Triiodothyronine