Androgens have a slight influence on the daily rhythms of behavior and metabolism in castrated male lambs.

Sex steroids can modulate the daily pattern of behavior, body temperature, and metabolism in sheep. However, in young male sheep, chronic androgen exposure is required to trigger changes on these patterns. The aim of this study was to compare the daily behavioral (eating, ruminating, standing, lying, and sleeping), body temperature (eye and rectal), glucose and insulin concentrations, and sensitivity to insulin patterns in 5-6-month-old male lambs castrated shortly after birth and acutely or chronically treated with androgens. Thirty male lambs were treated with: 1) a single im dose of 100 mg of cyclopentyl testosterone propionate 48 h before the recordings (AcT; n = 10); 2) three weekly im doses as the one administrated to AcT with the last simultaneous to the administration to the AcT lambs (ChT; n = 10); 3) no hormonal treatment, remaining as controls (Con; n = 10). The treatments modified only the acrophase of eating (P = 0.02) and the glycemic robustness (P = 0.04), without altering other characteristics of the daily pattern of the variables evaluated. The ChT lambs showed an ∼ 1-h delay in the acrophase of the percentage of time spent eating compared with the AcT lambs (P = 0.01), as well as greater glycemic robustness than the Con lambs (P = 0.03). Acute androgen treatment was ineffective, whereas chronic treatment only had a slight impact on the daily patterns evaluated. The rigidity exhibited in all the other responses studied reinforces the conclusion that these patterns, which result from evolution favoring animal adaptation to the light-dark cycle, are highly conserved.