The cow is then probably slaughtered for humans to enjoy. Humans would then produce some sort of excreta that needs to be disposed of. In the organic loop, the excreta would be returned to the earth as fertilizer to help the plants gain much needed nutrients, thus closing the organic loop. But this rarely happens. The waste is usually disposed of in some other manner.
Landfills are one solution, but in many countries they are filling up and closing down.
Also, landfills can leak toxins into groundwater and methane into the atmosphere making both of them harmful. They are not foolproof either. Sewage systems are very expensive, use lots of water, and sometimes mixed with industrial chemicals. When mixed with the chemicals, reuse of the waste becomes difficult and often hazardous. This may seem a little bleak, but there are some solutions that can be put into practice to help close the organic loop.