Journal Articles

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Author: search.filters.author.Lockwood ASubject: search.filters.subject.Merino

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    Decreasing Mob Size at Lambing Increases the Survival of Triplet Lambs Born on Farms across Southern Australia
    (MDPI (Basel, Switzerland0, 2023-06-09) Lockwood A; Allington T; Blumer SE; Boshoff J; Clarke BE; Hancock SN; Kearney GA; Kenyon PR; Krog J; Kubeil LJ; Refshauge G; Trompf JP; Thompson AN; Dailey R
    Industry consultation in Australia revealed that the potential impact of the mob size of ewes during lambing on the survival of triplet-born lambs was an important research priority. Previous research has demonstrated that smaller mob sizes at lambing improve the survival of single- and especially twin-born lambs, regardless of ewe stocking rate. Therefore, we hypothesised that lambing triplet-bearing ewes in smaller mobs, regardless of stocking rate, will increase the survival of their lambs. Research sites were established on 12 commercial sheep farms across southern Australia between 2019 and 2021. One farm used Merinos whilst the remainder of the farms used non-Merino breeds, consisting of composite ewes joined to composite or terminal sires. Three of the farms were used in two years of the experiment. Adult, triplet-bearing ewes were randomly allocated into one of two treatments, 'High' or 'Low' mob size, at an average of 135 days from the start of joining. Ewe and lamb survival were assessed between allocation to treatments and lamb marking. Lamb survival was significantly greater for lambs born in the Low (65.6%) compared with the High (56.6%) mob size treatments (p < 0.001). There was no effect of mob size at lambing on the mortality of triplet-bearing ewes. Analysis of the effect of the actual mob sizes showed that reducing the mob size at lambing by 10 triplet-bearing ewes increased the survival of their lambs to marking by 1.5% (p < 0.001). This study has shown that the survival of triplet-born lambs can be improved by lambing triplet-bearing ewes in smaller mobs regardless of stocking rate when ranging from 0.7-13 ewes/ha.
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    A review of dystocia in sheep
    (Elsevier B.V., 2020-11-01) Jacobson C; Bruce M; Kenyon PR; Lockwood A; Miller D; Refshauge G; Masters DG
    This review aims to describe the nutritional and non-nutritional factors that may affect parturition and dystocia in sheep. Dystocia is associated with fetopelvic disproportion, uterine inertia, failure of the cervix to fully dilate, malpresentation and disease or congenital defects in lambs. Dystocia can result in lambs that are born dead, or lambs that survive parturition but sustain birth injury including central nervous system damage. Dystocia risk is increased with high or low birthweight lambs, high (fat) or low liveweight ewes, and small first parity ewes. Other factors implicated include low muscle glycogen, pregnancy toxaemia, mineral imbalance causing hypocalcaemia, and a lack of antioxidant nutrients. Addressing these risks requires differential nutritional management for single and multiple bearing ewes. There is also evidence for stress and environmentally related dystocia. The stress related hormones cortisol, adrenaline and ACTH play a major role in the initiation and control of parturition in the sheep indicating a need for adequate supervision during lambing, provision of adequate feed and shelter at the lambing site, and small flock size to reduce physical and environmental stress. Hormonal control of parturition can be further disrupted by xenoestrogens or phytoestrogens in clovers and medics. Oestrogenic plants are still widely grown in mixed pastures but should be not be grazed by pregnant ewes. There is clearly a genetic component to dystocia. This is partly explained by incompatibility in physical size and dimensions of the ram, ewe and lamb. A rapid reduction in dystocia through direct genetic selection is problematic with low heritability of dystocia and some of its indicator traits such as lambing ease. This review provides broad interpretation of the literature, but conclusions are not definitive with widespread inconsistency in reported results. Further research is required to investigate dystocia under commercial production conditions, and this should be complemented by focussed studies under controlled conditions. Priorities include defining the fitness of the ewe to lamb, the role of stress and environment on parturition and the use of indicator traits to select for ease of birth.