Deducted from what? From gross adjusted Income, for the purposes of keeping you (the Borrower) below the Income limit for the program.
Remember, USDA Zero down loans have income limits which are determined by the entire income of the household.
Common deductions we immediately look for are for childcare expenses, minors living at home, full time students living at home, elderly folks 62+ yrs or older, disabled etc etc.
But medical expenses in excess of 3% of annual income maybe deducted. For a detailed breakdown, read this lengthy article.
USDA Loans & Medical Expense Deductions