Survival of twin lambs is increased with shrub belts

Perinatal lamb mortality is a major source of reproductive loss, particularly for twins. A study was conducted to determine whether provision of shelter in the form of shrub belts (a ‘maternity ward’) could increase survival of twin lambs compared with hedgerows, and whether hedgerows improve survival of single lambs compared with unsheltered paddocks. Measurements were recorded for Merino x Poll Dorset cross twin lambs born in hedgerows (phalaris or hessian) or shrub belts and single lambs born in hedgerows or unsheltered paddocks over the years 2007-2009. Records for 382 single and 726 twin lambs were used. The survival of single lambs was not increased (P = 0.06) by hedgerow shelter. The survival of twin lambs in shrubs was 10% higher (P < 0.05) than that in hessian hedgerow shelter in 2008-2009 (0.77 cf. 0.70), associated with a reduction in deaths from starvation and/or mismothering and/or exposure. The hessian shelter was associated with an increased (P < 0.05) growth rate to weaning of single lambs, but the growth rates of twin lambs were lower (P < 0.05) in shrub than in hessian shelter. In 2010, a second study of 178 twin Merino × Poll Dorset cross lambs found that survival of lambs born alive was not improved by shrubs compared with unsheltered paddocks (0.80 versus 0.77; P > 0.05). It is concluded that shrub belts which forced twin-bearing ewes to lamb in a sheltered environment reduced perinatal mortality in one of three datasets, but was not repeated. The shrubs take time to establish, and the benefit will be small if weather is mild during lambing.