Minerals play an essential role in the normal vital process. Calcium, phosphorus and magnesium are
the most abundant minerals. Vitamin D and parathyroid hormone play a key role in regulation of
their homeostasis as well. The aim of this study was to evaluate calcium, phosphorus, magnesium,
vitamin D and parathyroid hormone on 30 Caspian horses of Guilan Province (south of the Caspian
Sea) in two different seasons. So that, 15 stallions and 15 mares were sampled at the age groups ≤ 3
years and > 3 years, respectively. Fasting blood samples were collected twice, in August and January
2015 from jugular vein of horses. Serum calcium, phosphorus and magnesium were measured by
colorimetric methods, while 25(OH)D3 and parathyroid hormone were measured by ELISA. The
calcium (11.50 vs. 14.25 mg dL-1
), magnesium (2.13 vs. 3.72 mg dL-1
) and vitamin D (1.66 vs. 2.48 ng
mL-1
) levels were lower in winter than in summer (P < 0.05). The Caspian horses had higher
phosphorus (4.52 vs. 3.26 mg dL-1
) in winter than in summer (P < 0.05). Effect of sex on the measured
parameters was not significant. Effects of age on the calcium, magnesium, vitamin D and parathyroid
hormone levels were not significant, but ≤ 3 year - old horses had higher phosphorus (4.63 vs. 3.15 mg
dL-1
) than > 3 year - old ones (P < 0.05). The vitamin D level of mares was higher (3.10 vs. 1.43 ng
mL-1
) in summer than in winter (P < 0.05). Effects of sex, season, age and their interactions on
parathyroid hormone were not significant. In conclusion, calcium, phosphorus, magnesium and
parathyroid hormone levels in Caspian horses were within their physiological range, but vitamin D
was low without any signs of deficiency. The Caspian horses had lower calcium, magnesium and
vitamin D levels in winter than in summer
