Abstract
Artificial weaning is the separation of the mother and her lamb, involving the forced ending of suckling and milk supply by the ewes to their lambs. Artificial weaning time varies depending on the purpose of each sheep farm and the characteristics of the lambs, including age and weight of the lambs, and their ability to eat solid food. Artificial weaning is performed from 24 h postpartum until around the age of natural weaning (up to 12 mo of age). Artificial weaning results in the breaking of the ewe-lamb bond, the end of suckling and the complete replacement of milk by solid food, frequently added to changes in both the physical and social environment. It triggers behavioural, physiological and immunological changes that generate negative consequences on the health of both ewes and lambs, as well as on the growth of the lambs, rising animal welfare concerns. As artificial weaning is considered one of the most stressful situations in the life of farm mammals, it is important to consider the factors involved in those responses to develop adequate strategies and improve sheep welfare at weaning. The most frequently used method is the abrupt separation of the ewes and their lambs. However, the adaptation of the animals after weaning can be improved by alternative weaning methods (e.g., progressive, two-steps weaning and mixed regimes), hormonal treatments (e.g., administration of progesterone), and pre- and postweaning management (e.g., the use of creeping feeding, and the presence of conspecifics or humans after weaning). This review presents and summarises information on the stress response and animal welfare issues at artificial weaning in sheep and some management practises that can be used to reduce these problems. The major points included are the ewe-lamb bond at birth and during the lactation period; the stress response at weaning; the factors involved in the stress response at weaning; the different types and weaning methods and their repercussions on animal welfare; and some strategies that can be used to improve sheep welfare at weaning. Lastly, we propose directions for research needed to develop practical alternatives to minimise sheep's stress response at weaning.
Highlights
Sheep are precocial species that generally deliver 1–2 newborns, that can see, hear, stand up, and follow the mother shortly after birth
Ewes establish a selective bond with their lamb within a few hours after birth (Poindron et al, 2007; Mora-Medina et al, 2016), nursing only those that were recognised as their own offspring
Artificial weaning is performed before natural weaning age, which has been reported to occur at up to 12 mo of age in wild sheep (Geist, 1971; Grubb, 1974), and is characterised by the complete replacement of suckling by solid food or artificial rearing with sheep milk or milk substitute (Napolitano et al, 2008; Weary et al, 2008)
Summary
Sheep are precocial species that generally deliver 1–2 newborns, that can see, hear, stand up, and follow the mother shortly after birth. Ewes have a strong preference for their lamb; but as the strength of the preference decreases, the preference of the lamb for the dam increases (Hernandez et al, 2009; Maldonado et al, 2015) This change in social behaviour characterises the process of natural weaning and is associated with the decrease in suckling frequency, the increase in solid food consumption, and the waning of the bond (Weary et al, 2008). The duration of suckling and milk production by the dam decrease, and in parallel, the intake and time eating solid food by the young increase (Arnold et al, 1979; Freitas-de-Melo et al, 2018a) This reduction in suckling frequency, associated with the increase in solid feeding, favours rumen development (Lyford, 1988). Lambs prefer the company of their mother for more than 1 month after separation (Hinch et al, 1987; Ungerfeld et al, 2018), but after that, they do not show an important motivation to seek for their mother (Ungerfeld et al, 2018)
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