Decreasing the mob size but not stocking rate of ewes at lambing increases the survival of twin lambs born on farms across southern Australia
A. Lockwood
A F , J. Trompf B , L. Kubeil C , A. Thompson A , G. Refshauge D , G. Kearney E and S. Hancock A
+ Author Affiliations
- Author Affiliations
A College of Science, Health, Engineering and Education, 90 South Street, Murdoch University, Murdoch, WA 6150, Australia.
B J.T. Agri-Source, 2A Bradley Drive, Mill Park, Vic. 3082, Australia.
C Department of Economic Development, Jobs, Transport and Resources, 89 Sydney Road, Benalla, Vic. 3672, Australia.
D New South Wales Department of Primary Industries, Cowra Agricultural Research and Advisory Station, 296 Binni Creek Road, Cowra, NSW 2794, Australia.
E 36 Paynes Road, Hamilton, Vic. 3300, Australia.
F Corresponding author. Email: A.Lockwood@murdoch.edu.au
Animal Production Science 60(16) 1949-1958 https://doi.org/10.1071/AN19632
Submitted: 7 November 2019 Accepted: 14 May 2020 Published: 30 June 2020
Abstract
Context: Data collected from producers in south-eastern Australia found that the survival of twin-born lambs decreased by 3.5% for each extra 100 ewes in the mob at lambing. Increasing stocking rate by 1 ewe/ha decreased lamb survival by a further 0.7%. These survey findings suggest that lamb survival could be improved by optimising the allocation of ewes to mobs and paddocks at lambing.
Aim: The present paper reports two experiments. Experiment 1 tested the hypotheses that (1) the survival of twin-born lambs would be greater when ewes lamb in smaller mobs and at lower stocking rates, and (2) the effects of mob size and stocking rate would be greater in Merinos than in non-Merino breeds. Experiment 2 tested the hypothesis that the survival of twin-born Merino lambs would be greater at lower mob sizes when ewes lambed at stocking rates <4 ewes/ha.
Methods: Experiment 1 investigated a 2 × 2 factorial combination of mob size (high or low) and stocking rate (high or low) on the survival of twin-born Merino and non-Merino lambs at 70 on-farm research sites across southern Australia. Experiment 2 investigated the effect of high or low mob size on the survival of twin-born Merino lambs when ewes lambed at stocking rates of <4 twin ewes/ha at 15 on-farm research sites. In both experiments, adult twin-bearing ewes were randomly allocated into a treatment and lambing paddock on Day 140 from the start of joining at each farm. Lamb survival in each mob was calculated based on lamb losses between pregnancy scanning and lamb marking.
Key results: In both experiments, the effect of mob size on lamb survival was found to be linear, with survival of twin-born lambs decreasing by between 1.9% and 2.5% per additional 100 ewes in the mob at lambing, regardless of breed (P < 0.001). In Experiment 1, there was no effect of stocking rate or mob size by stocking rate on lamb survival.
Conclusions: The present research demonstrated that reducing mob size but not stocking rate will improve the survival of twin-born lambs to marking for extensive enterprises in Australia where ewes lamb at stocking rates of up to 12 ewes/ha.
Implications: These findings will contribute to guidelines for optimising ewe nutrition and resource allocation to improve lamb survival.
Additional keywords: lambing density, marking rate, Merino, non-Merino.
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