Changes in hormonal profiles during the estrous cycle in old lactating beef cows

Area of Science:

• Reproductive endocrinology in cattle
• Comparative physiology of aging livestock

Background:

• Hormonal fluctuations, including luteinizing hormone (LH), follicle-stimulating hormone (FSH), progesterone (P4), and estradiol-17 beta (E2), regulate the estrous cycle in cows.
• Aging can influence physiological processes, potentially affecting reproductive hormone dynamics.

Purpose of the Study:

• To compare the patterns of key reproductive hormones during the estrous cycle between young and old lactating beef cows.
• To investigate age-related differences in hormonal concentrations and their potential impact on follicular development and ovulation.

Main Methods:

• Hormone concentrations (LH, FSH, P4, E2) were measured throughout the estrous cycle in two age groups of lactating beef cows (young: 5-7 years; old: ≥12 years).
• Statistical analyses were performed to compare cycle length and hormone patterns between the age groups.

Main Results:

• No significant difference in estrous cycle length was observed between young and old cows.
• Age-specific differences were found in the patterns of P4 (days 1-15), FSH (days 6-12), and E2 during the follicular phase.
• Older cows showed an earlier midcycle FSH elevation, correlated with an earlier and higher E2 concentration during the follicular phase.

Conclusions:

• Subtle differences in FSH and P4 patterns suggest earlier or more advanced follicular development in older cows.
• Older cows exhibit enhanced estradiol-17 beta secretion from the preovulatory follicle, indicating age-related alterations in follicular dynamics.