Endocrine profiles and follicular development in early-weaned postpartum beef cows

Area of Science:

• Reproductive Endocrinology
• Veterinary Science
• Animal Reproduction

Background:

• Early weaning in postpartum cows can impair fertility.
• Progestagen treatment is known to improve fertility in postpartum cows.
• Understanding the hormonal mechanisms behind progestagen's effects is crucial for optimizing reproductive management.

Purpose of the Study:

• To investigate if progestagen treatment affects gonadotrophin concentrations (LH, FSH) and follicular development in postpartum cows.
• To compare the patterns of LH, oestradiol, and FSH secretion and follicular growth before the first postpartum ovulation between treated and control cows.

Main Methods:

• Two experiments were conducted on suckled, anoestrous beef cows.
• Cows received a progestagen (norgestomet) ear implant for 9 days or served as untreated controls.
• Calves were weaned 7 days after treatment initiation, and cows were monitored for oestrous behavior and hormonal profiles.

Main Results:

• Progestagen treatment significantly increased the proportion of cows forming a corpus luteum with a normal lifespan compared to controls.
• While overall patterns of LH, oestradiol, and follicular growth were similar, treated cows showed a transient rise in FSH associated with weaning, which was absent in controls.
• Norgestomet-treated cows exhibited a more rapid increase in mean LH and higher mean oestradiol levels in the 3 days preceding the preovulatory LH surge.

Conclusions:

• Progestagen treatment, specifically norgestomet, enhances fertility in postpartum cows, likely by improving corpus luteum function.
• The treatment influences gonadotrophin secretion patterns, particularly affecting LH and oestradiol dynamics around the preovulatory surge.
• These findings provide insights into the hormonal regulation of postpartum reproduction and the efficacy of progestagen therapy.