Seasonal plasma levels of luteinizing and steroid hormones in male and female domestic ostriches (Struthio camelus).

Ostriches are low-latitude birds and can be considered to be seasonal breeders. However, they are also opportunistic in that they can breed all year round. Monthly hormonal plasma concentrations were measured in six female and six male domestic ostriches kept at a latitude of 31 degrees 20'N. Measurements were made over a year, during which time each female laid an average of 28.7 eggs. Egg laying occurred between March and September, with peak numbers in May-June. Concentrations of plasma luteinizing hormone (LH) increased in February in both sexes and started declining before termination of egg laying. Plasma testosterone concentrations in males increased in April, about 2 months after the increase in LH. In females, plasma estradiol concentrations peaked in May but were elevated from March to August, basically all of the egg-laying period. Plasma hormonal changes in the ostriches were gradual and not abrupt, as seen in many wild seasonal breeders of higher latitude.