Solubility in water, 2% citric acid, and 0.4% hydrochloric acid of calcium-magnesium carbonate (dolomite) and magnesium carbonate (magnesite) from deposits in Poland, and of magnesium oxide and magnesium sulphate, were studied. The magnesium content in the compounds was 136.2, 277.6, 484.0, and 122.7 g Mg/kg DM, respectively. The solubility of magnesium from dolomite and magnesite in water was low and equaled 2.50 and 2.44 %, respectively. The solubility of magnesium in 2% citric acid was 78.73, 67.01, 79.52, and 76.09%, respectively, whereas in 0.4% hydrochloric acid is equaled 77.57, 80.68, 68.04, and 90.22%. The availability of magnesium was studied in a feeding experiment on 25 growing weathers, 5 animals per group, with a body weight of 30.2±1.8 kg, housed in balance cages. The weathers were fed a synthetic maintenance diet composed of (%): glucose (29), potato starch (28), cellulose (30), urea (4), sunflower oil (4) and minerals (5). The mineral mixture contained the studied magnesium salts. Magnesium intake equaled 800-1000 mg/animal/day. Apparent and true absorption of magnesium and its retention were studied assuming that the amount of endogenous magnesium excreted daily in faeces is 2.33 mg kg^-1 BW/day. Apparent retention of magnesium in weathers receiving dolomite, magnesite, magnesium oxide, and magnesium sulphate was 32.1, 16.3, 31.2, and 17.0% of magnesium intake. Apparent absorption of magnesium from the mineral salts equaled 32.6, 17.4, 37.6, and 21.0% of magnesium intake, respectively. True absorption equaled 38.8, 23.8, 44.9, and 29.9% of magnesium intake, respectively. Apparent retention, apparent absorption and true absorption in weathers receiving dolomite did not differ significantly from retention and absorption in animals receiving magnesium oxide, but were significantly higher than the respective values when magnesite and magnesium sulphate were fed. The magnesium level in the serum of weathers equaled 2.40 mg/100 ml in the control group, which did not receive magnesium. It was significantly higher (P<0.01) in the groups receiving dolomite, magnesite, magnesium oxide, and magnesium sulphate, and equaled 2.82, 2.63, 2.96, and 2.89 mg Mg/100 ml, respectively. The highest increase in the serum magnesium concentration was found in the weathers fed magnesium oxide, followed by magnesium sulphate and dolomite (P≤0.01). Administering magnesium oxide to weathers significantly lowered calcium absorption (P≤0.01).