High pre-weaning mortality rates continue to limit sheep production globally, constituting a major economic and welfare concern. Greater losses in twin lambs (≥ 30%) compared with singletons (≥ 10%) are attributed primarily to lower birthweight and increased risk of intrapartum hypoxia, leading to impairment of thermoregulation, neuro-motor activity, and maternal bonding behavior. Previous intensive studies demonstrated that supplementing pregnant ewes with melatonin reduced the adverse effects of fetal growth restriction and perinatal hypoxia on the neonatal brain via increased umbilical blood flow, placental efficiency, and antioxidant actions. The current study examined the effects of supplementing pregnant ewes with melatonin on lamb survival, birthweight, and behavior under intensive conditions. From gestational day 80 until parturition, pregnant singleton and twin-bearing ewes were supplemented with melatonin via a 2 mg capsule fed daily (Mel-FED, n = 61), or 18 mg subcutaneous implant (Regulin), with one implant administered at gestational day 80 and another at gestational day 125 (Mel-IMP, n = 60). Control ewes received no supplementation (CTL, n = 60). Ewes and lambs were monitored via video throughout parturition. Post-partum measures were taken from lambs at 4 h and 24 h (live weight (LW), rectal temperature, serum IgG, latency to stand and suck after birth), and LW at 72 h, 7 d, marking (49.7 ± 0.2 d) and weaning (124.2 ± 0.8 d). Chi-square analysis was used to compare lamb survival between treatment groups. There were no treatment effects on singleton lamb survival. Melatonin supplementation tended to increase the proportion of twin lambs surviving from birth to weaning (Mel-FED = 85.5%; Mel-IMP = 85.9%; CTL = 72.9%; each P < 0.1). Survival of first-born twins did not differ between treatment (each ~90%, P = 0.745) but within second-born twins, survival of Mel-FED was greater than CTL (81.6 versus 57.1%, P = 0.023), and Mel-IMP (78.1%) tended to be greater than CTL (P = 0.068). Similarly, in second-born twins exposed to prolonged parturition (≥ 90 min), survival of lambs from Mel-FED ewes was greater than CTL (86.7% versus 42.9%, P = 0.032), while Mel-IMP was intermediate (66.7%). These data suggest that the neuroprotective actions of melatonin may improve twin lamb survival by increasing tolerance of prolonged parturition, and provide a sound basis for continued testing in extensively managed sheep flocks.

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ContextThe high incidence of lamb mortality in Merino sheep is a persistent issue for the industry. Poor-quality colostrum or inadequate colostrum consumption increases the risk of low energy intake and failed passive immunity transfer, resulting in lamb mortality. The rapid assessment of colostrum quality and intake would be a valuable tool for producers which house ewes for lambing.AimsThis experiment determined the relationship and accuracy of analysis techniques to measure immunoglobulin G (IgG) and total protein (TP) concentrations within ewe colostrum and lamb serum and compared those results against digital hand-held refractometers.MethodsMerino ewe colostrum and lamb blood were sampled at 4 and 24 h post-partum during autumn (n=93 ewes) and spring (n=79 ewes) in 2018. Colostrum was analysed for total milk solids (%) and lamb serum was analysed for total blood serum protein (%), and both colostrum and lamb serum were analysed for IgG and TP using in-house laboratory analysis techniques. Correlation coefficients were performed to identify the relationship between the different assessment methods.Key resultsThere was a significant Pearson’s correlation (P<0.05) between 4 h total milk solids and TP (R=0.19), between total milk solids and IgG (R=0.19), and TP and IgG (R=0.38). For 24 h colostrum samples, the significant correlations (P<0.001) between TP and IgG (R=0.54) and total milk solids and IgG (R=0.56) were higher than the correlation between total milk solids and TP (R=0.24; P=0.006). Further, 4 h serum IgG (R=–0.14; P=0.026) and 24 h total blood serum protein (R=0.21; P=0.009) were correlated with lamb survival to 72 h.ConclusionsWhile the refractometer provided a crude measure of colostrum IgG and TP and was valuable in identifying lambs with low IgG transfer at 24 h, further research is required regarding analysis techniques to allow for reliable measures need to be refined.ImplicationsThe use of refractometers to assess colostrum quality and intake could benefit researchers or producers who practice indoor lambing.

Context Arginine supplementation can counter the negative effects of fetal growth restriction in ewes bearing multiple lambs by increasing birth weight and brown adipose fat stores in lambs; however ruminal degradation limits its bioavailability and necessitates ruminal protection. The arginine precursor citrulline increases circulating arginine after a single oral dose without ruminal protection, and bolus intravenous infusion of citrulline increases maternal and fetal circulating arginine for at least 4 h post infusion. Responses to oral and chronic citrulline have not, however, been evaluated in neonatal lambs. Aims This experiment sought to determine whether orally fed citrulline would increase circulating plasma concentrations of citrulline and arginine in pregnant Merino ewes. Methods Pregnant Merino ewes were fed citrulline (CIT, 8 g/day, n = 9) or no supplement (CON, n = 9) from Day 125 of gestation (DG 125) until parturition. Ewe (DG 125) and neonatal lamb serum (<2 h old) was analysed for circulating plasma citrulline and arginine concentrations. Key results Circulating concentrations of citrulline were higher in CIT than CON ewes 4 h post feeding at DG 125, and in CIT compared to CON neonatal lambs. Despite higher citrulline concentrations, supplementation did not increase maternal or neonatal circulating arginine concentrations. Conclusions Maternal supplementation with this dose of citrulline was not effective in increasing circulating levels of arginine. Implications Further studies may be merited in pregnant sheep to determine whether higher doses of oral citrulline can increase arginine availability during gestation.