Jean is exactly correct. If ...

Jean is exactly correct. If attempting this  I fell you need to take a step back and consider the short and long term.  First at the end of this journey you wish to have a food a cow can consume. = $ .  Then you need to find out what foods are acceptable that the cow WILL consume.  Next whenever you want a certain waste item clean through plant root system look up (online) plant nutritional requirements. They will have the element, and ppm acceptable. use this info for cow too. If there is ever a concern of pathogens or toxicity simply add an RNA microbial group to the medium which the selected plant grows.  Never a no answer. Just learn how to work with the established parameters of both plant and animal.