Perinatal lamb survival was not reduced by grazing forage oats
Susan M. Robertson
A B * , Michael A. Friend A C , Bruce Allworth B D and Marie Bhanugopan B
A
B
C
D
Abstract
Grazing forage oats (Avena sativa) is perceived as a risk to perinatal lamb survival and grazing oats only during the lambing period has reduced lamb survival.
This study assessed whether perinatal lamb mortality differed for ewes grazing a legume-based pasture throughout the lambing period compared with those grazing oat forage during lambing.
A randomised design used two replicates each of two litter sizes (singles or twins) in two forage treatments. Mature Merino ewes were used (n = 424; 53 per group) and all groups grazed legume-based pasture from 6 weeks prior to the start of the lambing period. Control ewes remained on legume pastures, whereas Oat groups were moved to forage oats 9–11 days before lambing. A calcium, magnesium and sodium loose lick supplement was offered to all groups.
Ewe mortality was 1.2%, mainly in twin-bearing ewes and similar among treatments. Lamb birthweights were similar; however liveweight at marking was greater for lambs that were born on the legume pastures than for those born on the oats (13.1 ± 0.19 and 12.5 ± 0.18 kg; P = 0.041). Lamb survival did not differ (P = 0.192) between ewes grazing oats (87.3 ± 3.4%) and those grazing legume pasture (78.1 ± 3.4%), and resulted in 1.28 versus 1.14 (P = 0.143) lambs marked/ewe. Lamb survival was similar (P = 0.102) for singles (89.2 ± 3.2%) and twin lambs (76.2 ± 3.2%). Loss in condition score during the lambing period was reduced (P < 0.001) by grazing oats (−0.2 ± 0.06) compared with legume pasture (−0.6 ± 0.06).
Lamb survival was not reduced by grazing oats rather than legume pasture during the lambing period, although further replication is needed, given the large numerical difference. Any difference in survival between oats and a legume-based pasture when ewes are offered a calcium, magnesium and sodium supplement may depend on the capacity of forage to meet the energy requirements of ewes, although taller oats potentially provide shelter from wind chill.
Grazing forage oats during the lambing period has variable effects on lamb survival associated with the relative ability of alternative pasture to provide adequate nutrition, with positive impacts possible.
Keywords: husbandry, management, mortality, nutrition, pasture, reproduction, sheep, survival.
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