The effect of mid-pregnancy shearing or yarding stress on ewe post-natal behaviour and the birth weight and post-natal behaviour of their lambs

Abstract

This study was undertaken to determine whether a 24-h fast plus intensive yarding could duplicate the increase in lamb birth weight associated with mid-pregnancy shearing, thereby avoiding the potentially harmful effects of shearing ewes in a cold climate. Mixed-age Romney ewes bearing singleton ( n = 138) or twin lambs ( n = 115) were assigned to one of three treatment groups; control, yarded or mid-pregnancy shorn. Yarding and mid-pregnancy shearing took place on day 79 of pregnancy. Throughout pregnancy ewes were managed as a single mob until 1 week prior to lambing. Within twelve hours of birth the lamb's weight, body dimensions and behaviour were recorded. The ewes' maternal behaviour was determined during this period. The liveweight of twin-bearing ewes was significantly greater than their singleton-bearing counterparts ( P < 0.05) but did not differ between treatment groups. Lambs born to ewes that were shorn during mid-pregnancy were significantly ( P < 0.05) heavier by 0.4 and 0.5 kg at birth than lambs born to ewes in either the control or yarded treatment groups, respectively. Lambs born to shorn ewes were significantly heavier at weaning by 1.7 kg than lambs born to yarded ewes ( P < 0.05). Lambs born to ewes in the shorn treatment had larger girths (41.0 vs. 38.9 and 39.7 cm) and crown–rump-lengths (CRL) (56.9 vs. 54.9 and 55.6 cm) than lambs born to ewes in both the control and yarded treatments. Ewe treatment had little effect on ewe and lamb behaviour. The absence of a significant difference in the birth weight and body size between lambs born to yarded and control ewes and the significant difference between shorn and yarded treatments indicates that yarding stress is not the mechanism responsible for the birthweight increase from mid-pregnancy shearing.