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.