Onset of puberty and duration of seasonal cyclicity in Lipizzan fillies.

The research investigates the onset of puberty and cyclicity in Lipizzan fillies to better understand the breed’s hormonal changes. The researchers discovered that this onset and cycle duration is largely influenced by seasonal factors, although exceptions indicate that other factors also play a role.

Objective

The primary objective of the study was to determine the onset of puberty and the progression of cyclicity in young Lipizzan mares from ages 1 to 4. Researchers aimed to fill in gaps of knowledge about hormonal changes at puberty and seasonal cyclicity in this breed, which had been mostly based on empirical data.

Methods

• 46 Lipizzan fillies from ages 1 to 4 were chosen for the study.
• For a period of 2 years, blood samples were taken twice a month from the fillies.
• An Enzyme-Linked Immunosorbent Assay (EIA) kit was used to measure progesterone concentrations, which served as indicators of ovarian activity.
• Values above 6.4 nmol/l indicated a luteal phase (post-ovulation), and those under 3.4 nmol/l meant estrus, the period in the reproductive cycle when the mare is receptive to breeding.

Results

• Half of the studied Lipizzan fillies entered puberty during the first spring after their birth, at an average age of 15.25 months. The other half entered puberty during the second spring, at an average age of 25.2 months.
• In several cases, the estrus began in March and reached its peak between June and September. This was commonly observed in fillies of all ages, who exhibited anestrus (periods of sexual inactivity) during the winter months.
• The length of time spent in estrus was noted to be age-dependent, with 1-year-old fillies spending an average of 2.37 months in this phase, and 4-year-old fillies spending about 8.56 months.
• In December, more than half of the 2 to 4-year-old fillies were still in their estrus phase and some entered anestrus in January of the following year.
• A small proportion of 3 to 4-year-old fillies remained cyclic throughout the entire year, suggesting that factors other than photoperiod may be involved in regulating seasonal cyclicity.

Conclusions

The study demonstrated that seasonal factors significantly influence the onset of puberty and the progression of estrus activity in most Lipizzan fillies. Despite these findings, exceptions were observed, reinforcing the existence of other factors regulating cyclicity. However, the researchers were not able to specifically identify reasons for these prolonged periods of estrus activity and propose that future research should explore the role of the hormone leptin.