Upon the release of a female fox squirrel we raised, one of the first things we saw her do was to pull up tufts of lawn grasses and flip them over to chew on the soil that surrounded the roots. It was many years later that I learned that this instinctual behavior of tree squirrels of ingesting soil (geophagy), is a common behavior in many mammals, by which they obtain calcium and other minerals, along with, 'soil based organisms' (SB0) aka: "microbiota", which for tree squirrels are vital to support the degrading of, 'oxalates' in stem and leaf parts of plants, which otherwise significantly limit the availability of calcium they contain, and some even have been found to lower calcium in other foods consumed in the same meal.
(Reference: "Digestibility" pg. 40, "The Natural History of Tree Squirrels" by John Gurnell)
By providing a source of (SBO) in support of captive diets, that doesn't include damaging parasites and/or bad bacteria as soil otherwise may, lends support to the breaking down of cellulose walls of the stems and leaf part of plants in the intestinal tract.
Pet Flora by Vitality Science, is an unflavored, 'soil based bacteria', with no flavors or fillers.
A source some here have added to the rodent block and greens, organic food grade Chia oil from, "Foods Alive", has also improved the acceptance of block diets also. Other sources of chia oil which are carrier oils should not be included in food for pets.
https://www.amazon.com/Vitality-Scie.../dp/B005PJN2HO