Fostering lambs by odor transfer: Two-lamb substitution

Abstract

Odor specific to individual lambs enables ewes to discriminate between their own and alien offspring. Previous research has demonstrated that many post-partum ewes will adopt a single alien lamb in addition to their own natural lamb if the alien lamb is wearing a jacket impregnated with own-lamb odor (“add-on” odor transfer fostering technique). The following study investigates whether a higher percentage of ewes will adopt “extra” lambs if their own natural young is exchanged for 2 alien lambs (two-lamb substitution). Cloth stockinettes were placed on the natural lambs of 47 multiparous ewes shortly after parturition. Forty-eight to 72 h later, 27 ewes that had given birth to single lambs and 20 ewes that bore twins were given 2 alien lambs in exchange for their own offspring. Approximately half of the ewes in each group received alien lambs wearing jackets impregnated with own-lamb odor (experimental odor transfer group); the remaining ewes received aliens wearing their own jackets (control group). Standard acceptance tests were conducted daily for 5 days. Only 14.3% of the experimental (odor transfer) ewes that bore single young accepted both alien lambs in exchange for their own. However, 90% of the experimental ewes that bore twins accepted both aliens. Control ewes had lower adoption rates of alien lamb pairs. Ewes bearing single young tended to accept only 1 lamb. Experimental ewes that received siblings (twins) were more likely to accept both alien young than ewes that received non-siblings (57.1 vs. 30%, respectively). Ewes that bore single lambs were more likely to accept a single alien lamb if they were presented with non-sibs than sibling pairs (84.6 vs. 42.9%, respectively). It was concluded that two-lamb substitution via the odor transfer fostering technique is inferior to the add-on procedure for increasing the number of lambs reared by ewes. However, it is an effective method for replacing twin sets that have died.