Variability in neonatal behaviour in single and twin lambs

Abstract

The effect of litter size (LS) on the variability in neonatal behaviour in the context of lamb survival was investigated. Merino ewes (n=270) were oestrus synchronised in three mating groups (MG) 10 days apart and naturally mated. Eighteen ewes from each MG were selected, balanced for LS (singles and twins) following pregnancy scanning at day 60. Ewes were maintained on pasture until day 100 of pregnancy before being fed a concentrate ration in group pens. Ewes were housed five days prior to lambing, in individual pens. Video records from birth until three hours post partum were taken and times to stand, reach the udder, unsuccessfully and successfully suckle determined. At 10-15 minutes post partum, lambs were removed for blood sampling and morphometric and temperature measurement. MG3 lambs also had an infrared thermal image taken and consequently, were separated from their dams 1 minute longer (P<0.05) than MG1 and 2 lambs. Data were analysed using Proc GLM (SAS) with LS and MG plus their interaction included as terms in the model. MG was added as it was a potential source of variance. There was a significant interaction (P<0.05) between LS and MG for times to stand and reach the udder. Twins were quicker to stand than singletons in MG1 (15.4 and 31.0 min) and MG2 (18.8 and 29.3 min) but this was reversed in MG3 (42.4 and 20.6 min). Similar trends were observed for time to reach the udder (MG1 20.4 and 42.4 min; MG2 31.0 and 39.7 min; MG3 57.1 and 38.5 min). Singletons did not differ in times to perform these behaviours between MG. The reasons for this MG effect in twins are unclear. The additional time away from the ewe or more exposure to high quality Spring pasture for MG3 compared to the other groups could have contributed.