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 (P(4)) and estradiol-17beta (E(2)beta). 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) P(4) levels were 93.2% higher before than after oviposition and increased with 43.1% for every 3 h closer to oviposition; when LH and E(2)beta levels and V(F1) increased with 1 ng/ml, 10 pg/ml and 10 ml, respectively, P(4) increased with 116.6%, 50% and 6.1%; and (iii) E(2)beta 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.