Seasonal differences in ovarian activity in cows.

Area of Science:

• Reproductive Endocrinology
• Animal Physiology
• Veterinary Science

Background:

• Seasonal influences on animal reproduction are well-documented but require specific investigation in cattle.
• Understanding seasonal effects on ovarian function is crucial for optimizing livestock breeding and management.

Purpose of the Study:

• To investigate seasonal variations in luteinizing hormone (LH), prolactin, and key ovarian function parameters in cows.
• To determine if seasonal differences in gonadotropin secretion correlate with changes in ovarian activity.

Main Methods:

• Plasma concentrations of LH and prolactin were measured in cows across different seasons (May-June vs. October).
• Ovarian parameters including follicle size, granulosa cell counts, corpus luteum weight, and progesterone secretion were assessed.
• LH responsiveness and granulosa cell aromatase activity were evaluated.

Main Results:

• Higher LH peak frequency and prolactin concentrations were observed in October (spring) compared to May-June (autumn/winter).
• Cows in May-June exhibited larger dominant and estrogen-secreting follicles with more granulosa cells.
• Corpora lutea were heavier and secreted more progesterone in May-June than in October, indicating enhanced luteal function.

Conclusions:

• Significant seasonal differences in ovarian activity exist in cattle.
• These seasonal variations are likely driven by corresponding changes in the secretion of pituitary gonadotropins.