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The absence of a corpus luteum formation alters endocrine profile and follicular development during the first follicular wave in cattle

K Hayashi, National Institute of Agrobiological Sciences, Tsukuba, 305-8602, Japan
M Matsui, Department of Clinical Veterinary Science, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Japan
T Shimizu, Animal and Food Hygeine, Obihiro University, Obihiro, Japan
N Sudo, Graduate School of Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Japan
A Sato, Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Japan
K Shirasuna, Graduate School of Animal and Food Hygiene, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Japan
M Tetsuka, Department of Agricultural and Life Science, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Japan
K Kida, Field Center of Animal Science and Agriculture, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Japan
D Schams, Instutute of Physiology, Technical University of Munich, Freising-Weihenstephan, Germany
A Miyamoto, Animal and Food Hygiene, Obihiro University, Obihiro, Japan

Correspondence: Kengo Hayashi, Email: hayaken{at}affrc.go.jp

Abstract

We previously established a bovine experimental model showing that the corpus luteum (CL) does not appear by aspiration of the preovulatory follicle before the onset of luteinizing hormone (LH) surge. Using this model, the present study aimed to determine the profile of follicular development and the endocrinological environment in the absence of CL with variable nadir circulating progesterone (P4) concentrations during the oestrous cycle in cattle. Luteolysis was induced in heifers and cows and assigned to either aspirate the dominant follicle (CL-absent) or induce ovulation (CL-present). Ultrasound scanning to observe the diameter of each follicle and blood collection were performed from the day of follicular aspiration or ovulation and continued for six days. CL-absent cattle maintained nadir P4 throughout the experimental period and showed a similar diameter between the largest and second largest follicle, resulting in codominant follicles. Oestradiol (E2) concentrations were greater in CL-absent cows than in CL-present cows at Day -1, Day 1 and Day 2 from follicular deviation. CL-absent cows had a higher basal concentration, area under the curve (AUC), pulse amplitude and pulse frequency of LH than CL-present cows. After follicular deviation, CL-absent cows showed a greater basal concentration, AUC and pulse amplitude of GH than CL-present cows. These results suggest that the absence of CL accompanying nadir circulating P4 induces an enhancement of LH pulses, which involves the growth of the codominant follicles. Our results also suggest that circulating levels of P4 and E2 affect pulsatile GH secretion in cattle.