## 4 Discussion  
In the mountainous rural areas where the current survey took place, geography has shaped two different farming practices. Steep slopes, plains and valleys determine in obvious and subtle ways the animal husbandry. Farms in the higher altitude are more remote and tend to be more traditional. The animals of these herds are of mixed breeding descending from autochthonous breeds. They are very well adapted to the harsh weather and are also very resistant to various diseases. It is for these reasons and certainly not their inferior productivity, which makes them ideal for this ecosystem. Their main source of nutrition is grazing the surrounding pastures which are rather meagre, and this factor poses an upper limit to the size of the herd. Additionally, a small amount of concentrate is provided every evening. Milking is performed manually. The other type of farming is observed in the lower altitudes. There the pastures are greener and the distances smaller. The survival of the animals is not dependent on the environmental conditions. The animals are housed in better conditions, still graze all day long, but they also receive a rich nutritious supplement of hay and various concentrates, a fact which allows larger herds, superior breeding animals and milking parlours. Regardless the type of farm milking, this is performed twice per day and the milk is stored in each farm's cooling bulk tank. The present survey is an attempt to address the question if the bulk tank milk reflects the differences in the type of farming with respect to various safety and quality issues. In the market, quite a few commercial kits are available for the detection of the antibiotic residues in milk. They are sensitive to different groups of antimicrobial substances and their function is based on the same principle, that is the inhibition of bacterial growth in the presence of antimicrobial residues. It is a semiquantitative method in which the bacterial growth in negative samples is marked by change in the color of the substrate, while in positive ones there is no bacterial growth, and the color of the substrate remains unchanged [38]. Usually, the indicator organism is _B. stearothermophilus_, while bromoresol serves as the color index (remains purple in positive samples and turns yellow in the negative ones). However, one thing is the result, and another thing is the biological interpretation of the result. The inhibition of bacterial growth can be affected by other factors, which inhibit the bacterial growth and eventually lead to false positive results. Such factors are (i) the presence of natural substances in the milk such as the bacteriocins, (ii) \begin{table}
\begin{tabular}{c c c} \hline \hline
**Microorganism** & **Antibiotic** & **\% Resistance** \\ \hline  & amoxicillin-clavulanic acid (20–10 \(\upmu\)g) & 75 \\ \cline{2-3}  & ampicillin(10 \(\upmu\)g) & 87.5 \\ \cline{2-3}  & aztreonam (30 \(\upmu\)g) & 0 \\ \cline{2-3}  & cefotaxime (5 \(\upmu\)g) & 0 \\ \cline{2-3}  & ceftiofur (30 \(\upmu\)g) & 0 \\ \cline{2-3}  & cefazidime (10 \(\upmu\)g) & 0 \\ \cline{2-3}  & chloramphenicol (30 \(\upmu\)g) & 12.5 \\ \cline{2-3}  & enrofloxacin (5 \(\upmu\)g) & 0 \\ \cline{2-3}  & imipenem (10 \(\upmu\)g) & 12.5 \\ \cline{2-3}  & kanamycin (30 \(\upmu\)g) & 12.5 \\ \cline{2-3}  & oxytetracycline (30 \(\upmu\)g) & 50 \\ \cline{2-3}  & streptomycin (30 \(\upmu\)g) & 37.5 \\ \cline{2-3}  & sulfatethoxazole-trimethoprim (23.75–1.25 \(\upmu\)g) & 37.5 \\ \cline{2-3}  & tetracycline (30 \(\upmu\)g) & 75 \\ \cline{2-3}  & 3 rd generation cephalosporors and clavulanate & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: _Cont._higher somatic cells content of the milk and (iii) presence of detergents and disinfectants in the milk [39; 40; 41; 42]. It is for these reasons that any positive results should be further confirmed by more sophisticated methods. False negative results occur in cases of test failure or in cases where the implicated antibiotic residue is out of the range of detection of a particular test.