The objective of the study was to determine whether the coat cover in Polish Konik mares is more dense in winter than in summer and whether the possible difference is effected by the system of the horses’ maintenance, lactation or age. Thirty three Polish Konik horses were included: 23 mares kept in a stable and pasture/paddock, and 10 mares living on a close reserve. The study was conducted in July and December, hence summer and winter coats were analysed. The measurements were taken from single horses. Nineteen mares were examined in both seasons, whereas five mares were studied only in the summer and other nine mares only in the winter which resulted in 52 measurements in total. The mares were split into four age groups. Most of mares in both groups lactated in summer, whereas in winter only reserve mares had foals at foot. The coat hair density was determined from the horse’s scapula, where an approximately 9cm2 area was shaved to obtain hair 0.5mm in length. Photographs of this area were taken and after conversion a 1mm2 square net was put on the picture to enable counting the hair leavings. The measurement was the number of hairs in 1cm2. Data were analyzed using three-way ANOVA with repeated measures (summer, winter), considering two factors: the system of maintenance (stable, reserve) and lactation (lactating mares, non-lactating mares). The age group factor was considered in an additional two-way ANOVA with repeated measures. Spearman’s correlation, Pearson’s correlations, regression and determination coefficients were determined. The results showed that the coat hair density is a symptom of primitive horses’ adaptation to changing environmental conditions. The hair density is significantly higher in winter than in summer, and the density in summer and winter is correlated. The coat hair is denser in reserve mares that are subject to more severe conditions than in stable mares. In winter, the coat hair density increases with the mares’ age, which may be associated with higher requirements for isolation from harsh conditions in older mares. The coat hair density is not related to the mare’s lactation. These findings may be important for improving the welfare of stable horses.