SOME FACTORS INVOLVED IN NATURAL WEANING PROCESSES IN SHEEP

Two studies were done to define the factors influencing the time of natural weaning in sheep. The milk production of ewes was measured during four-hour periods each week at varying stages of lactation. Lambs were separated from the ewes during this period before being reunited and the behavioural responses of each to the other were recorded. The responses were classed according to an arbitrary system defined to gauge the current strength of ewe-lamb attachments. In the first study, measurements were made on Merino and Dorset Horn sheep. Whilst milk yield declined continuously during lactation, the nature of ewe-lamb bonds did not. They remained constant up to about 100 days after birth. Thereafter, the attachments weakened rapidly, with some differences between the two breeds. In the second study, Merino ewes on a high plane of nutrition had a higher milk yield throughout lactation than ewes on a low plane of nutrition. The ewe-lamb bond remained unchanged for 130 days in the high plane group but changed substantially in the low plane group. It is concluded that milk yield in the ewe is a major determinant of the strength of the ewe-lamb bond, with a threshold level below which weaning occurs. © 1979.