Like all ruminants, deer need a proper rumen environment to maintain the populations of microbes that digest the plants they eat. Normal rumen pH is very mildly acidic. However, too much starch, especially if consumed in a short time, results in a great deal of lactic acid being produced in the rumen. This drops the pH, making the rumen much more acidic and killing off the vital microbes. This can result in founder, acidosis and even death.