Follicle Dynamics and its Relation with Plasma Concentrations of Progesterone, Luteinizing Hormone and Estradiol during the Egg-Laying Cycle in Ostriches

The aims of this study were (i) to describe the changes in the volume of large ovarian follicles (diameter >3 cm) during the 48 h egg laying cycle in farmed ostriches, and (ii) to quantify factors affecting the volume of the largest measured follicle and the plasma concentrations of progesterone (P₄) and estradiol‐17β (E₂β). In eight egg‐producing birds, which all ovulated during the study period, transcutaneous ultrasound scanning and blood sampling was performed at 3 h intervals. The average volume of the total number of visualized large follicles (V_total), the largest measured follicle (V_F1), the second largest follicle (V_F2) and of all follicles smaller than F2 (V_F3–Fn) were each higher before than after oviposition. V_total, V_F2 and V_F3–Fn nearly doubled in the 24‐h period before oviposition, while V_F1 remained at an equal, rather high level until oviposition. Immediately after oviposition V_total, as well as the volume of the other follicle categories, decreased within 6 h, i.e. around the moment of ovulation. By performing statistical analysis on the basis of linear mixed‐effects modelling, we quantified that: (i) V_F1 was 13.2% higher before than after oviposition and increased with 6.5% when LH increased with 1 ng/ml; (ii) P₄ levels were 93.2% higher before than after oviposition and increased with 43.1% for every 3 h closer to oviposition; when LH and E₂β levels and V_F1 increased with 1 ng/ml, 10 pg/ml and 10 ml, respectively, P₄ increased with 116.6%, 50% and 6.1%; and (iii) E₂β levels were 35.6% higher before than after oviposition, increased with 2.7% for every 3 h closer to oviposition and increased with 14.6% when LH increased with 1 ng/ml. It is concluded that during the egg‐laying cycle in ostriches: (i) follicular mass, as estimated by the volume of visualized follicles larger than 3 cm, increases before and decreases after ovulation, and (ii) follicular dynamics and its accompanying endocrine plasma hormone profiles during the egg‐laying cycle in ostriches follow a pattern similar to that in chickens.