Mother–young behaviours at lambing in grazing ewes: Effects of lamb sex and food restriction in pregnancy

• We studied the effect of pasture allowance during pregnancy in ewe–lamb bonding.
• We mimicked natural pasture availability during gestation.
• Male lambs’ suckling times were negatively related to duration of food restriction in pregnancy.
• Latency to lick lambs tended to be greater in ewes with a longer period of food restriction.

This study investigated whether the level of pasture allowance from before conception until late pregnancy affects ewe–lamb behaviours at birth, and if those behaviours differ according to the sex of the lambs. We performed two experiments, in which 96 ewes were assigned to one of two nutritional treatments: high native pasture allowance [10–12 kg of dry matter/100 kg of body weight (BW)/day] or low pasture allowance (5–8 kg of dry matter/100 kg of BW/day). In Experiment 1, treatments began 23 days before artificial insemination and ended at 122 days of gestation (groups HPA-1, n = 38; and LPA-1, n = 25 for high and low pasture allowance, respectively), and in Experiment 2, started 40 days before artificial insemination and ended at 105 days of gestation (groups HPA-2, n = 22; and LPA-2, n = 11 for high and low pasture allowance, respectively). Thereafter, all ewes received rice bran (200 g/animal/day) and 50 mL of crude glycerine/animal/day. Ewes’ body condition score (BCS) and BW were recorded at lambing. Latency from parturition to licking her lamb, maternal behaviour score (MBS; a test that evaluates maternal attachment to the lamb), lambs’ BW, and latency to stand up and suckle were recorded. In Experiment 1, HPA-1 ewes had greater BCS and BW (2.5 ± 0.04 units vs. 2.25 ± 0.05 units and 52.7 ± 0.4 kg vs. 50.2 ± 0.4 kg, respectively; P < 0.0001) at lambing, and tended to lick their lambs earlier (1.4 ± 0.3 min vs. 1.9 ± 0.3 min; P = 0.08) than LPA-1 ewes. Male lambs of LPA-1 ewes suckled later than female lambs (73.3 ± 11.7 min vs. 43.4 ± 13.1; P = 0.02), male (73.3 ± 11.7 min vs. 45.5 ± 10.8; P = 0.02) and female lambs of HPA-1 ewes (73.3 ± 11.7 min vs. 49.4 ± 10.3; P = 0.04). In Experiment 2, BCS and BW at birth were similar between HPA-2 and LPA-2 ewes. In addition, behaviours of lambs and ewes, as well as MBS were not affected by nutritional treatment or sex of the lambs, and there was no interaction between nutritional treatment and sex of the lambs. In conclusion, different native pasture allowances from before conception until advanced pregnancy followed by a great increase in nutritional plane during late pregnancy, did not affect ewe–lamb behaviours at lambing. However, slight sex differences were detected when duration of food restriction during gestation was longer.