 The mass death and illness of cattle drastically affected dairy production, and the output did not return to its pre-pestilence amount until 1331.Much of the medieval peasants' protein was obtained from dairy, and milk shortages likely caused nutritional deficiency in the European population.Famine and pestilence, exacerbated with the prevalence of war during this time, led to the death of an estimated ten to fifteen percent of Europe's population.