Circadian rhythm of calciotropic hormones, serum calcium, phosphorus and magnesium during the shortest and longest days of the year in horses in New Zealand.

The research article explores the variation in circadian rhythms of certain hormones and mineral concentrations in horses during the shortest and longest days of the year. The findings, which indicate a significant difference in these parameters during different seasons, could impact how equine athletes are managed during international travel for competitions.

Research Methodology

• The research was performed on five healthy adult horses, all following a consistent pasture feeding regimen.
• To collect data, blood samples were taken from each horse every three hours over a 48-hour period, starting at 7 PM on the first day and ending at the same time on the third day.
• The study was conducted twice, once during the shortest day of the year and once during the longest day of the year in 2013.
• The samples were then used to measure the quantity of calciotropic hormones including vitamin D metabolites, such as 25-hydroxyvitamin D, 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D, and parathyroid hormone – as well as concentrations of serum calcium, phosphorus, and magnesium in the horses’ blood.

Research Findings

• There were significant differences in serum concentration of calciotropic hormones, serum ionized calcium (iCa), total calcium (tCa), phosphorus (P), and total magnesium (tMg) between the shortest and longest days of the year.
• The concentration of 25-hydroxyvitamin D was consistently low, and even undetectable at times.
• Certain concentrations, including ionized calcium, 1,25-dihydroxyvitamin D, and parathyroid hormone, showed a clear circadian rhythm on the longest days, whereas total calcium, phosphorus, and magnesium concentrations followed a diurnal pattern on the longest (summer) days.
• None of the analysed elements displayed any circadian rhythm on the shortest (winter) days of the year.

Significance of the Study

• The research results have potential implications for equine athletes that travel to international equestrian competitions, as these horses face substantial time and seasonal differences which could disrupt their ability to adjust their circadian rhythms to new time zones.
• Understanding these patterns can provide insights into optimal management and scheduling strategies, which could improve the well-being and performance of these equine athletes.