Fostering lambs by odor transfer: the substitution experiment.

Lamb-specific odor is used by ewes to discriminate between their own and alien offspring. The objective of the present study was to investigate the feasibility of transferring own-lamb odor to alien young to facilitate fostering. Shortly after birth, cloth stockinettes (body suits) were placed on the offspring of 37 multiparous ewes. At 48 to 72 h after parturition, a lamb from each ewe was replaced by an alien lamb. In 31 cases the odor-impregnated stockinette of the ewe's own lamb was placed on the alien lamb; in the remaining six cases the alien lamb retained its own stockinette (control condition). Lamb acceptance tests were conducted every 12 h for 2 d after fostering and once daily for the following 2 d. Twenty-six of the 31 experimental ewes (84%) adopted alien lambs using the odor-transfer technique. All of the control lambs were rejected. Of the 26 ewes that adopted foster young, 10 (38%) showed immediate acceptance and 22 (85%) were exhibiting acceptance behaviors by 36 h after fostering. There were no significant differences in the fostering success of ewes bearing single lambs and those with twins. The presence of own-lamb odor rather than the absence of alien lamb odor appears to be the salient cue for lamb acceptance. Lamb-specific odor transfer represents a relatively inexpensive and rapid technique to achieve maternal acceptance of alien lambs by postpartum ewes.