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Table 2 Overview of reproductive and metabolic hormones in captive African elephants and Asian elephants

From: Clinical health issues, reproductive hormones, and metabolic hormones associated with gut microbiome structure in African and Asian elephants

Reproductive hormones Function African (n = 61) Asian (n = 38)
Progestagens (ng/ml) Produced by the corpora lutea of ovary, involved in pregnancy and menstrual cycle, concentrations increase after ovulation Continuous
Range: 0.052–0.607
Median: 0.17
Mean: 0.21
Continuous
Range: 0.052–0.562
Median: 0.25
Mean: 0.25
Prolactin
PRL (ng/ml)
Produced by the anterior pituitary, promotes lactation, involved in normal follicular function, maintains homeostasis [118, 119] Continuous
Range: 2.44–105.24
Median: 11.57
Mean: 17.40
Continuous
Range: 2.34–21.26
Median: 5.25
Mean: 6.30
Luteinizing hormone
LH (ng/ml)
Produced by the anterior pituitary, initiates ovulation, develops and maintains corpus luteum Continuous
Range: 0.59–2.64
Median: 0.99
Mean: 1.08
Continuous
Range: 0.47–3.45
Median: 1.24
Mean: 1.36
Follicle-stimulating hormone
FSH (ng/ml)
Produced by the anterior pituitary, promotes follicular development Continuous
Range: 1.07–5.53
Median: 2.66
Mean: 2.73
Continuous
Range: 2.84–7.38
Median: 4.11
Mean: 4.42
Metabolic hormones Function African (n = 61) Asian (n = 38)
Fecal glucocorticoid metabolites
FGM (ng/g)
Produced by the adrenal cortex; functions in metabolizing carbohydrates, proteins, and fats [45, 46], induces glucose synthesis [47]. Often used as a measure of chronic physiological stress in wildlife [48] Continuous
Range: 21.02–249.53
Median: 84.22
Mean: 93.68
Continuous
Range: 20.92–328.29
Median: 108.20
Mean: 128.13
Thyroid stimulating hormone
TSH (ng/ml)
Produced by the anterior pituitary, TSH stimulates the thyroid gland to produce T4, which can be transformed into T3 [120] Continuous
Range: 0.19–1.73
Median: 0.85
Mean: 0.88
Continuous
Range: 0.12–1.88
Median: 1.04
Mean: 1.07
Total triiodothyronine
Total T3 (ng/dl)
  Continuous
Range: 38.04–117.64
Median: 85.7
Mean: 85.52
Continuous
Range: 52.06–165.89
Median: 95.97
Mean: 98.38
Total thyroxine
Total T4 (µg/dl)
Produced by the thyroid gland, T4 and T3 control metabolism, homeostasis, and growth [121, 122]. T4 and T3 circulate in plasma bound to transport protein and unbound. Unbound hormone is referred to as “free”, whereas “total” measures bound and unbound hormone. Free T4 moves to target organs where it is transformed to T3 Continuous
Range: 6.77–14.72
Median: 9.46
Mean: 9.75
Continuous
Range: 6.48–12.64
Median: 10.02
Mean: 10.20
Free thyroxine
Free T4 (ng/dl)
Continuous
Range: 0.49–1.17
Median: 0.84
Mean: 0.83
Continuous
Range: 0.44–1.23
Median: 0.71
Mean: 0.75
  1. Description of general function and range of reproductive and metabolic hormones in African and Asian elephants (dataset includes zoos with two or more elephants)