The ‘ram effect’ as a way of modifying the reproductive activity in the ewe

The seasonality of breeding activity in sheep represents an important constraint in the breeding program of commercial flocks. The ‘ram effect’ is one among various techniques available to manipulate reproduction during the anoestrous season but with the advantages of being inexpensive, of easy application and free from causing problems to the consumer of animal foods (i.e. hormone residues). The aim of this paper is to summarize the most important aspects of the ram effect, including the nature of the ram stimuli involved, the behavioural and physiological events elicited in the ewe as a result of the presence of the ram, the neuroendocrine basis of the phenomenon and the various factors associated with variation in response. The effects of a wide range of social relationships on reproductive activity in sheep and other species are also discussed. © 2002 Elsevier Science B.V. All rights reserved.