Out-of-season breeding and ewe-lamb bond from birth to weaning in Corriedale sheep

Abstract

Out-of-season lambing is based in productive aims; however also modifies the basic physiology of the ewe. It might affect ewes and lambs’ behaviours at birth, their bond, the process of lambs’ independence from their mothers and their response to weaning. This study aimed to compare the ewe-lamb bond from birth to artificial weaning in out-of-season lambing (autumn) and spring lambing. A complementary aim was to determine if out-of-season breeding affects ewes' udder size, milk yield and composition, body condition score (BCS) and body weight of the ewes and lambs. The study was performed with 26 multiparous single-lambing Corriedale ewes that lambed in spring (natural season: group SPR), and 26 ewes that lambed in autumn (out-of-season: group AUT) and their lambs. The ewe-lamb behaviours were recorded during a separation-reunion test performed 24–36 h after birth. Lambs’ behaviours were recorded before and after weaning (at 80 days of age). Ewes’ BCS and body weight were recorded at mating, lambing and weaning. Lambs’ body weight was recorded at lambing, before and after weaning. Ewes’ milk yield and composition were determined before weaning. During the separation-reunion test, although AUT lambs vocalised more often than SPR lambs their mothers remained further away (P = 0.01). Before weaning, AUT ewe-lamb dyads were observed more often far from each other (P < 0.001); AUT lambs attempted to suckle more times (P < 0.001) and grazed less frequently than SPR lambs (P = 0.004). At weaning, AUT lambs walked more frequently, but were less often standing up than SPR lambs (P < 0.001 for both behaviours). While SPR lambs decreased their grazing frequency on the day of weaning, AUT lambs increased it, grazing more frequently than SPR lambs (P < 0.001). AUT ewes lambed with a greater BCS and body weight than SPR ewes (P = 0.01 and P = 0.031, respectively), but this was reverted at weaning (BCS: P < 0.001; body weight: P = 0.002). SPR ewes had a greater milk yield, with more fat, lactose and protein amount than AUT ewes (P < 0.001 for all variables). At weaning, SPR lambs were heavier than AUT lambs (P < 0.001). In conclusion, although AUT ewes were in better body condition after birth, the ewe-lamb bond of the AUT group was weaker. This was associated with a lower expression of maternal attention when AUT lambs requested maternal care. The better environmental conditions of SPR dyads during lactation might positively impact their social and nutritional behaviours. The difference between groups remained until weaning, so AUT and SPR lambs displayed different behavioural strategies to cope with artificial weaning.