Wefare implications of artificial rearing and early weaning in sheep

Soon after parturition a lasting and mutual ewe–lamb bond is established. However, in an increasing number of intensive sheep farms, lambs are separated from the dam at an early age. When artificial rearing is applied lambs are often kept with mothers for 2 days to allow the ingestion of maternal colostrum and then abruptly removed from their dams. Thus, lambs experience a marked emotional stress represented by the loss of the most relevant social model at this early stage of their behavioural development and a nutritional stress represented by the transition from maternal milk to a commercial milk substitute. These animals when exposed to open field tests show reduced levels of vocalization, are slower to initiate movements, spend less time in ambulatory behaviour and display an increased cortisol response than non-separated animals. In addition, artificial rearing performed on lambs from 2 days of age onward can cause decreased cellular and humoral immune responses. The main oral abnormal behaviour performed by artificially reared lambs is represented by sucking the navel or the scrotum of pen mates. This activity is evident from the initial days on reconstituted milk and lasts until weaning from milk. Attempts have been made to reduce the detrimental effects of early separation. Some of them mainly focus on the emotional aspects (it is recommended not to leave a lamb alone for artificial rearing), others aim at reducing the nutritional impact of artificial rearing (milk intake can be increased by offering a mix of ewe milk and a milk replacer during the first week and then gradually moved to a diet based only on milk substitute which results in higher growth rates). As compared with artificial rearing, early weaning performed at 3 months of age is associated with a later disruption of the mother–young bond and the consequent direct replacement of maternal milk by solid food. However, when they are given the chance, ewes and their lambs form long-term social associations which exceed the age of natural weaning, regarded as the end of the milk feeding period. Early weaned lambs emit an increased number of high pitched bleats immediately after weaning than before and this increment is still evident 2 days afterwards. Neither partial nor gradual separation from mothers is able to reduce the stress associated with early weaning. In conclusion, premature separation from mothers has clear and marked detrimental effects on various functions in lambs. For lambs maternal deprivation seems to be worse at 2 days (artificial rearing) than at 3 months of age (early weaning)