Circadian variations in biochemical markers of bone metabolism in horse of different age

The author studied in thirty thoroughbred horses the influence of age and gender on daily rhythms of serum osteocalcin (oc). the animals were divided into two groups. group a: six male and six female 2 years old; group b: six male,six female and six geldings 6 years old. they were housed individually in box-like stalls under natural photoperiod and environmental conditions. blood samples were collected every 3 hours over a 48 hour period. statistical differences of serum oc concentration due to different gender were observed in both groups a and b. daily rhythms of serum oc concentration were observed only in group b,with nocturnal acrophase. in females the acrophase was statistically postponed for 1 hour compared to male and gelding. male and female showed a more robust daily rhythm than the geldings. the results showed that blood sampling for determination of serum oc should be strictly standardized with regard to the time of the day.