In mammals, lactation is the most energetically demanding component of female reproduction. Theory predicts an increase in food intake by lactating females, but very few studies have used contraceptives to experimentally test the influence of reproduction on foraging behaviour of wild mammals. From 2009 to 2011, we observed 182 individually marked female eastern grey kangaroos, Macropus giganteus, in two populations, including 29 that received an experimental contraceptive treatment. We sought to determine whether lactating females increase their foraging rate compared to contracepted and naturally nonlactating females. The proportion of time spent foraging during 10 min focal samples did not vary according to reproductive status in one population. In the other, lactating females spent 4% less time feeding than nonlactating females. Day and midday activity and bite and chewing rates were higher in lactating than in nonlactating females. Bite rate increased with the size of the pouch young and was higher for mothers of sons than for mothers of daughters. Bite rate was also affected by reproductive effort in the previous year, being higher for females that had weaned a young. Foraging behaviour was independent of body mass and group size, but bite rate appeared to decrease with female age. In one population, we found strong effects of date and year on foraging behaviour. Our study is a rare experimental manipulation of reproduction in free-ranging large mammals. We found that foraging behaviours were affected by both previous and current reproductive effort and varied with individual characteristics and environmental conditions.