First is the source, find out how long the ingredients to be used for your feeds have stayed in the feed mill, check the physical features of the feed and water. These include the color, odor and if possible the taste.
The final step is to take your feed and water sample to the laboratory of your choice for test. It is in the laboratory that you will request for whatever you like to test on the feed and water. The tests usually include tests for microbial content; Aflatoxins can also be tested for in the feed.
There is also a test to confirm the presence of salmonella organisms in your feed or water. These tests are however better carried out with the guidance of your consultant/expert because what you are looking for will determine the kind of test you will request for and A Vet. Doctor will make recommendations for the necessary tests.