Seasonal changes in serum progesterone levels in Caspian mares

The present study was conducted to assess the seasonal breeding of Caspian horses in ۱۰ mares during a year. Mares were divided into two age groups: ۳-۶ years (young) and ۷-۱۹ years (old). Blood samples (n=۵۳۰) were collected weekly. The ovarian activity was evaluated by the concentration of progesterone. Mares with serum progesterone concentrations consistently higher and lower than ۱ ng/ml were considered cyclic and non-cyclic, respectively. Results showed an interaction between time and age on the concentration of serum progesterone, ovarian activity, body weight, and body condition score (BCS) (p < ۰.۰۵). In March, the concentration of serum progesterone was higher in young mares (۷.۸۴ ± ۱.۱۴) than in old mares (۱.۲۶ ± ۱.۱۴, p < ۰.۰۵).  The serum progesterone was higher in old mares than in young mares during July-November (p < ۰.۰۵). Ovarian activity was higher in young mares than in old mares during February-April (p < ۰.۰۵). Ovarian activity was higher in old mares than in young mares during July-November (p < ۰.۰۵). The length of the breeding season was higher in old mares than in young mares (p < ۰.۰۵). BCS was higher in young mares (۴.۴ ± ۰.۲۲) than in old mares (۳.۲ ± ۰.۲۲) in February (p < ۰.۰۵). Body weight was lowest in the young mares during September-January (p < ۰.۰۵). There was a significant correlation between ovarian activity and BCS of Caspian mares. Finally, seasonal breeding was shorter and earlier in young Caspian mares compared to old mares.