The evolution of metallothionein (ZnMT) levels and haematological parameters in clinical and subclinical forms of copper deficiency in dairy cattle

Metallothioneins are cysteine-containing proteins involved in haemostasis and the transport of zinc and copper in the body. The aim of this study was to determine the effects of copper, anaemia and metallothioneins on the severity of clinical signs in clinical, subclinical, and atypical forms of copper deficiency. The study also attempted to determine normal metallothionein reference values for dairy cattle. The study has been carried out on 67 Holstein-Friesian cows; the animals were separated into 6 groups. Some animals showed typical clinical signs indicative of copper deficiency (two groups of study animals) and low Cu concentrations in the blood. In one group of cows, there were atypical clinical signs, and the average Cu concentration was 11.15 μmol l^-1. In 3 study groups, no clinical signs were observed, while the average copper concentration was equal to: 14.23 μmol l^-1, 13.30 μmol l^-1 and 9.87 μmol l^-1. Blood haematology test in all animals showed normocytic hypochromic anaemia. The authors noted that in the group with a decrease in the concentration of Cu in the blood and a high ZnMetallothionein (ZnMT), no clinical symptoms were observed in the animals, not even those related to anaemia. Clinical signs were also found to be less pronounced in cows with the highest serum Cu deficiency and significantly higher ZnMT content than in the other groups of cows with clinical signs. The conducted observations of the examined cattle in relation to Cu deficiencies, anaemia and MT content in the blood are very promising.