The Estrous Cycle in Cattle Physiology and Endocrinology

The Estrous Cycle in Cattle: Overview

• Influence on cattle reproduction and associated physiological processes.

• Authors: Freddie N. Kojima, Ph.D. and David J. Patterson, Ph.D.

• Department of Animal Sciences, University of Missouri.

Follicle Development

• Follicular Wave Phases:

  • The process consists of five phases:

  • Recruitment: The initial phase where follicles begin to grow.

  • Selection: Follicles undergo further selection for continued growth.

  • Growth: Selected follicles grow in size.

  • Dominance: A dominant follicle emerges.

  • Regression: The process by which non-dominant follicles regress.

• Typically, 2 to 4 follicular waves occur during the estrous cycle in cattle.

Role of Hormones in Follicle Development

Follicle Stimulating Hormone (FSH)

• Function:

  • FSH is essential for the recruitment of follicles, stimulating them to start growing.

• Applications:

  • Used in procedures for superovulation and embryo transfer in cattle.

Luteinizing Hormone (LH)

• Function:

  • LH promotes additional follicle growth and maturation of eggs.

Development and Ovulation

• Interaction of LH and Estrogen:

  • LH stimulates follicle growth.

  • Growing follicles produce high levels of estrogen.

  • Elevated estrogen levels induce the behavioral and physiological signs of estrus and lead to an LH surge that triggers ovulation.

Estrous Cycle Length

• For cattle with three follicular waves, the estrous cycle typically lasts 20 to 24 days.

• For cattle with two follicular waves, the estrous cycle is usually 18 to 20 days, slightly shorter than that with three waves.

Endocrinology During the Estrous Cycle

Follicle Stimulating Hormone (FSH) Levels

• Estrous cycle illustrated with 3 follicular waves in a 21-day cycle demonstrates the fluctuations of FSH.

Luteinizing Hormone (LH) Dynamics

• The cycle shows fluctuations of LH, with specific surges linked to ovulation.

• LH pulses regulate the estrous cycle and contribute to the timing of ovulation.

Estrogen Role

• Estrogen levels increase leading to ovulation during the estrous cycle, particularly in relation to LH dynamics.

Corpus Luteum Development

• Development and Function:

  • The corpus luteum (CL) develops from the ovulated follicle approximately 10 days after ovulation.

  • The CL is critical for producing progesterone, a hormone that maintains pregnancy.

Role of Prostaglandin F2α (PG)

• Function:

  • Late in the estrous cycle, the uterus produces PG which causes the CL to regress.

• PG is associated with commercial products like:

  • Lutalyse®

  • Estrumate®

  • ProstaMate®

  • In Synch®

Maintenance of the Corpus Luteum

• When a cow becomes pregnant, the presence of an embryo prevents the uterus from producing PG which would cause regression of the CL.

• This maintenance is crucial for ongoing progesterone production, ensuring the continuation of pregnancy.

Progesterone's Role in LH Regulation

• Progesterone regulates the discharge pattern of LH pulses, thus influencing follicular development.

Interrelationships Among Hormones

• Discussion of the relationships among estrogen, progesterone, and PG, and their regulatory roles throughout the estrous cycle, especially in a complete 21-day cycle incorporating 3 follicular waves.