In vitro penetration and absorption of chemicals into the ovine hoof

Techniques are described for testing the ability of chemicals to penetrate through ovine hoof horn. Most chemicals tested had penetration rates of less than 0.1 mm per hour and formalin, a chemical widely used for treatment of foot rot, penetrated very poorly (less than 0.02 mm per hour). Chloramphenicol in ethanol solution gave the highest penetration rate (0.21 to 2.38 mm per hour) and other penetrative chemicals were zinc sulphate (0.06 to 0.58 mm per hour), copper sulphate (less than 0.05 to 0.38 mm per hour) and sodium azide (less than 0.05 to 0.24 mm per hour) in aqueous solution. Inclusion of sodium lauryl sulphate in treatments enhanced the penetration rates of zinc and azide approximately sixfold. Ethanol and nickel ammonium hydroxide also improved the penetration of zinc and azide, particularly through the hard horn from the abaxial wall of the claw. Absorption of zinc from solutions containing 10 per cent zinc sulphate gave hoof tissue concentrations of zinc from 0.22 to 0.88 mg zinc ions per g tissue (10 to 20 times that found in normal hoof samples) and most of this zinc was retained after the horn was washed continuously in running water for 24 hours.