Seasonal changes in serum progesterone levels in Caspian mares

The present study was conducted to assess the seasonal breeding of Caspian horses in 10 mares during a year. Mares were divided into two age groups: 3-6 years (young) and 7-19 years (old). Blood samples (n=530) were collected weekly. The ovarian activity was evaluated by the concentration of progesterone. Mares with serum progesterone concentrations consistently higher and lower than 1 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 < 0.05). In March, the concentration of serum progesterone was higher in young mares (7.84 ± 1.14) than in old mares (1.26 ± 1.14, p < 0.05).  The serum progesterone was higher in old mares than in young mares during July-November (p < 0.05). Ovarian activity was higher in young mares than in old mares during February-April (p < 0.05). Ovarian activity was higher in old mares than in young mares during July-November (p < 0.05). The length of the breeding season was higher in old mares than in young mares (p < 0.05). BCS was higher in young mares (4.4 ± 0.22) than in old mares (3.2 ± 0.22) in February (p < 0.05). Body weight was lowest in the young mares during September-January (p < 0.05). 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.