Well, we have about 30 trillion of our own cells, and maybe 37 trillion bacterial cells to help us digest our food. Cows might weigh 250-1000kg (a quarter of a tonne to a tonne), which is between 3.5 and 14 times more than your average human, so maybe they’d have 105-420 trillion cells? At a very rough guess! They’d probably have proportionally more bacteria too – they only eat plants, which don’t like being food and make life very difficult for things that try and digest them. Cows have four parts to their stomachs to help them do this well, and bacteria are a hugely important part of that.