**4. Discussion**

#### *4.1. Biochemistry and Haematology*

Among the effects of knotweed on horse health, the following aspects are worth noting.

#### 4.1.1. Total Protein, Globulins and Albumin/Globulin Ratio

The concentration of total protein represents the sum of the protein fractions in plasma: of albumin and all the fractions of globulins. Compensations occur between proteins in plasma because decreases or increases in their concentrations are common [36,37], which means that the concentration of total protein is totally dependent on the concentrations of these two groups of proteins.

Globulins are mainly involved in the immune response, transport of substances and coagulation [38]. In equine plasma, globulins account for a large proportion of the total protein. Five different groups of globulins are recognized: alpha 1 and alpha 2 globulins, beta 1 and beta 2 globulins, and gamma globulins. Altogether they account for 40–50% of the serum protein content, the remaining 50–60% of the plasma protein content is albumin. The albumin/globulin ratio is a convenient means of comparing values among horses.

In this study, concentrations of globulins in the blood of knotweed-fed horses were higher and the A/G ratio was lower than in the blood of control horses. All the values were within physiological limits and no pathology was observed in any of these experimental horses. Increased levels of globulins are often accompanied by decreased levels of albumins. Low levels of albumin may result from the decreased production of albumin or the increased loss of albumin via the kidneys, gastrointestinal tract, skin or extravascular space, or from increased catabolism of albumin [31]. Here, non-significantly lower level of albumin could indicate decreased absorption of proteins in the gu<sup>t</sup> in the presence of knotweed, resulting in globulin increase, as globulins take over some of the functions of albumin. The increase of globulins suggests that the immunity of the horses was under non-specific pressure; the immunity of control horses was reduced, and their antibody levels decreased. On the contrary, the antibody levels in the stallions fed knotweed did not decline.

Increasing the plasma globulin concentration is desirable but difficult, as there are only a few means of doing so. Knotweed supplementation thus represents a suitable method.
