Washing lambs and confinement as aids to fostering

The effects on maternal behaviour, of washing lambs and of confining ewes with alien lambs for several days, were examined in groups of Merino ewes that had lambed approximately 1, 3, 9 or 27 days previously. In the 1-, 3- and 9-day groups, 25–43% of ewes refused to allow their own washed lambs to suck and 7–47% permitted a washed alien to suck, though most were able to distinguish their own washed lamb from 2 washed aliens in a multiple choice test. In the 27-day group, all ewes permitted only their own washed lamb to suck. Similar results were obtained in the 4 age groups with the same lambs when only the hind half was washed, indicating that odour from this region is responsible for releasing suckling behaviour.

When ewes were penned together with washed alien lambs for at least 2 days, 73–100% of lambs in the 1-, 3- and 9-day groups either gained weight progressively or were seen to suck freely from the foster mother, while only 33% of lambs in the 27-day group were similary accepted. With unwashed lambs, the acceptance rate was approximately half that of washed lambs. Labelling the alien lamb with wool from the tail region of the foster ewe's own lamb also tended to facilitate fostering, but not to any marked extent. Where the ewe's own lamb was also present in the flock after fostering, foster ewes tended to revert to suckling their own lamb at the expense of the foster lamb, especially in the 9- and 27-day groups.

The use of washing coupled with close confinement appears to be an effective method of fostering lambs on to ewes, especially within the first day or two after birth.

Fifty-five % of ewes in the 1- and 3-day groups failed to accept their own unwashed lamb after being separated from it for only 40–48 h, indicating that the ewe's memory for lamb odour is transient and/or that the odour changes with time.