Neonatal lamb mortality: major risk factors and the potential ameliorative role of melatonin
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(2020) 11:107
REVIEW
Open Access
Neonatal lamb mortality: major risk factors and the potential ameliorative role of melatonin Tom Flinn1* , David O. Kleemann2, Alyce M. Swinbourne1, Jennifer M. Kelly2, Alice C. Weaver2, Simon K. Walker2, Kathryn L. Gatford3, Karen L. Kind1 and William H. E. J. van Wettere1
Abstract High incidences of pre-weaning mortality continue to limit global sheep production, constituting a major economic and welfare concern. Despite significant advances in genetics, nutrition, and management, the proportion of lamb deaths has remained stable at 15–20% over the past four decades. There is mounting evidence that melatonin can improve outcomes in compromised ovine pregnancies via enhanced uterine bloodflow and neonatal neuroprotection. This review provides an overview of the major risk factors and underlying mechanisms involved in perinatal lamb mortality and discusses the potential of melatonin treatment as a remedial strategy. Supplementing pregnant ewes with melatonin enhances uterine bloodflow and fetal oxygenation, and potentially birthweight and neonatal thermogenic capacity. Melatonin freely crosses the ovine placenta and blood-brain barrier and provides neuroprotection to the fetal lamb during periods of chronic and acute hypoxia throughout gestation, with improved behavioural outcomes in hypoxic neonates. The current literature provides strong evidence that maternal melatonin treatment improves outcomes for lambs which experience compromised in utero development or prolonged parturition, though to date this has not been investigated in livestock production systems. As such there is a clear basis for continued research into the effects of maternal melatonin supplementation during gestation on pre-weaning survival under extensive production conditions. Keywords: Lamb survival, Melatonin, Neonatal mortality, Reproduction, Sheep
Introduction High pre-weaning mortality limits sheep production globally, with the proportion of lamb deaths across many countries and systems remaining stable at 15–20% over the past 40 years [1]. In Australian flocks, average losses of 10% and 30% for singleton and twin lambs, respectively [2, 3], cost the industry an estimated $540 million annually in lost production and in amelioration strategies [4]. Predominant causes of death can differ between regions depending on exposure to risk factors such as disease or * Correspondence: [email protected] 1 Davies Livestock Research Centre, School of Animal and Veterinary Sciences, The University of Adelaide, Roseworthy, SA, Australia Full list of author information is available at the end of the article
extreme weather [1], though there is a consensus that the majority of losses occur in the first 3 d post-partum [2, 5, 6]. In extensively grazed flocks, around half of all losses are parturition-related, comprising stillbirth (21%), birth injury (18%), and dystocia (9%), followed by starvationmismothering (25%), death in utero/prematurity (10%), predation (7%), and cold exposure (5%) [6]. Lamb birthweight a
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