Influence of low pasture allowance during pregnancy on the attachment between ewes and their lambs at birth and during lactation

Nutrient restriction during pregnancy may negatively affect ewe-lamb attachment at birth. We hypothesised that the difference in the attachment at birth could persist during lactation and, consequently, the emotional response of lambs to a short-term maternal separation test during late postpartum would be affected. The aim of this study was to compare the ewe-lamb attachment behaviours at birth and the behavioural response to a short-term maternal separation test of 3-month-old lambs born from dams that grazed on high or low natural pasture allowance from day 30 to day 143 of gestation. A complementary aim was to determine if milk yield and lambs' BW would be affected by the dams' pasture allowance during pregnancy. Forty-one multiparous single-lambing Corriedale ewes were randomly assigned to two natural pasture allowances: a) high (group HPA: n = 22): the ewes grazed on 14-20 kg of dry matter (DM)/100 kg of body weight (BW)/day; and b) low (group LPA; n = 19): ewes grazed on 6-10 kg of DM/100 kg of BW/day. From day 100 of gestation until lambing, the ewes were collectively provided with 300 g/animal/day of rice bran. From day 143 of gestation until lambs were 3 months old, all animals grazed on natural pasture with unlimited forage availability. Body condition score (BCS) of ewes and BW of ewes and lambs were recorded during the experiment, and udder size was recorded at lambing. Mother-lamb attachment behaviours were recorded at birth and ewes' milk yield was determined at 3 months of age, when lambs were subjected to a short-term maternal separation test. During the treatments, the HPA ewes had greater BCS and BW than the LPA ewes (p < 0.0001 for both). Birth weight was greater (p = 0.0001) in the HPA than the LPA lambs. At 45 and 91 days postpartum, lambs and ewes from the HPA group tended to be heavier than those from the LPA group (p < 0.08 and P < 0.06 respectively). The HPA ewes had greater udder volume (p = 0.002) at birth and produced more milk (p = 0.04) than the LPA ewes. The HPA ewes tended to have a greater frequency of high-pitched bleats (p = 0.07) and aggressive behaviours towards an alien lamb (p = 0.1) than the LPA ewes. All the other behaviours recorded at birth and variables recorded during the short-term maternal separation test were not affected by the treatment. Low pasture allowance from early gestation until lambing, in association with supplementation in advanced pregnancy, affected ewes' BW, BCS and milk production, lambs' birth weight, and slightly modified ewes' rejection towards an alien lamb. However, it did not modify the main ewe-lamb behaviours at birth and the lambs' emotional response to a short-term separation from their mother at 3 months of age.