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Behavior of Ewes and Lambs Subjected to Restraint Fostering¹

University of California, Davis 95616

Abstract

The objective of this study was to investigate the development of maternal-filial social attachments between ewes and alien lambs using the technique of "restraint fostering." Forty-eight to 72 h after parturition, 22 Targhee-type ewes were separated from their natural lambs, placed in restraining devices (stanchions) and each exposed to a single alien lamb. After a period of 1 or 4 d of restraint, the ewes were subjected to five 10-min lamb acceptance tests over a 48-h period. The observer recorded butts and butt attempts by the ewe and successful and unsuccessful suckle attempts by the lamb. The ewe-lamb pairs were then housed in pens with other groups of ewes and lambs and observed intermittently for acceptance behaviors. Six of the 14 ewes restrained for 4 d and none of the eight ewes restrained for 24 h met the criterion for successful adoption within 48 h. After being housed in group pens, adoptions were achieved by three ewes in the 1-d group and an additional four ewes in the group restrained for 4 d. Ewes restrained for 24 h were significantly more aggressive toward fostered young than ewes restrained for 4 d. In addition, the proportion of successful suckling attempts was significantly lower for lambs fostered on ewes in the 1-d group. Both groups showed a decline in butts and butt attempts over successive acceptance tests, but while the proportion of successful suckling attempts declined for lambs housed with 1-d ewes, they increased over time for lambs fostered on ewes restrained for 4 d. Vocalization frequencies of ewes when separated from their natural lambs could not be used to predict fostering success. The average weaning weight of fostered lambs was well within the normal range for naturally reared lambs at the same location. It was concluded that fosterings initiated 2 to 3 d after parturition are successful in the majority of cases if the ewe is restrained in a pen with the alien lamb for 4 or more days, followed by a period of unrestrained cohabitation as a pair and subsequent exposure to groups of females with young.

¹ The authors gratefully acknowledge the assistance of R. Sundburg, J. Hay, G. Dow and S. Wallach

² Dept. of Anim. Sci.

³ Present address: 8424 Curry Rd., Dixon, CA 95620