There can be many compounds in plants that are not directly toxic but with enough ingestion will cause a decline in health. Several plant compounds even mimic hormones in the body that can be helpful or harmful. CBD products from hemp or marijuana with the thc that causes all the psychoactive properties removed contains cannabidoids that can replace the endocannabinoids in mammals for improved mental health, sleep quality, and reducing pain or inflammation. Phytoestrogens on the other hand are typically considered bad for overly stimulating estrogen receptors beyond what the body produces and leading to reproductive related issues. At small amounts or in certain situations these things will do nothing but in other situations such as breeding small animals that tend to eat a lot of fresh food if they can those unknowns in the plant could contribute to vague problems breeders already spend lots of time tracking down before deciding if it's a genetic issue in the herd. There are some sites that will report the main chemicals known to effect the body even when it's not commonly used for ingestion or if it's high in an otherwise harmless compound but I can find nothing.
I have test fed things I was uncertain about to one or 2 animals if it was already around or easy for me to collect for feeding but it's a gamble that might not be worth the headache. More commonly I do that for guinea pigs that benefit greatly from a diet of fresh foods or use the guinea pigs as "guinea pigs" to find good chewing wood for their chinchilla relatives who constantly need a source of fresh wood for destruction or they'll rip apart the softer aluminum wheels and dismantle the water bottle springs in boredom. It's not really worth the potential risk for rabbits that are hard to adjust to fresh food, do fine on dry diets you can buy in bulk, and are just as happy to get a new source of hay or some grain based horse treats as greens.
