Onset of puberty in pasture-raised Thoroughbreds born in southern hemisphere spring and autumn.

The research article investigates the time, age and bodyweight factors impacting puberty onset in Thoroughbred horses born in both Autumn and Spring. The findings reveal that the onset of puberty in these horses is linked to seasonal changes in day-length as well as reaching a certain threshold bodyweight.

Objective and Methodology

• The aim of this study was to explore the age, bodyweight, and timing of puberty onset in Thoroughbreds born in Spring and Autumn. This was prompted by the lack of clear data on these factors due to varying descriptions of the puberty onset in these creatures.
• A total of 59 Thoroughbred horses that were pasture-raised were examined in the study. Colts and fillies born in Autumn and Spring were examined from birth until they reached 13 and 17 months respectively.
• The researchers measured the body weight of the horses and collected blood samples to identify the onset of puberty. For colts, a testosterone concentration more than 2 standard deviations above the baseline indicated puberty. For fillies, a first ovulation was signified by a progesterone concentration over 2 ng/ml, three times higher than the previous concentration.

Results

• The results showed that Spring-born fillies and colts were generally heavier and older at puberty compared to the those born in Autumn. Specifically, Spring-born foals reached puberty between 291-408 days weighing between 302-409kg, while Autumn-born foals reached puberty between 212-270 days weighing between 277-344 kg.
• Despite these differences, the average date of puberty onset was not significantly different between Spring and Autumn born horses. Puberty occurred mainly in October which is New Zealand’s Spring season.

Conclusions

• The research concluded that photoperiod seasonal changes and reaching a certain threshold bodyweight both influence the timing of puberty onset in Thoroughbreds.
• Spring-born horses were found to reach the required bodyweight threshold during the winter months and remained reproductively inactive until after the period of increasing day-length. As for Autumn-born horses, they achieved the necessary weight to support puberty at the same time as the stimulating photoperiod, resulting in them reaching puberty younger and lighter than the Spring-born horses.