Calcium and magnesium supplementation of ewes grazing pasture did not improve lamb survival

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Context Grazing of cereal forage crops is perceived as a risk for increased perinatal lamb mortality. Aims This study evaluated whether grazing oat forage during late pregnancy and/or the lambing period increased lamb mortality compared with grazing a legume (lucerne)-based pasture. Methods Merino ewes (n = 636) were allocated to two replicates of two litter sizes (singles or twins), which grazed the following three forage treatments: either legume-based pasture or oat forage (Avena sativa) from 42 days before and throughout a 4-week lambing period, or a legume-based pasture until 9–12 days pre-lambing before grazing oats throughout the lambing period. All groups were offered a calcium, magnesium and sodium mineral supplement to reduce the risk of deficiency. Key results Lamb survival to marking was similar for ewes grazing legumes (84.2 ± 1.94%) or oat forage (78.5 ± 1.94%) throughout, but was reduced (P = 0.022) for ewes that grazed oats only during the lambing period (71.0 ± 1.94%) compared with those that remained on legumes. The latter was associated with a greater (P = 0.016) loss of condition score in the ewes. The weight of lambs at marking age was 2 kg higher (P ≤ 0.05) when grazed on legume-based pasture during the 4 week lambing period rather than oats. Minimal ewe mortality (0.47%) occurred, no metabolic disease was observed and few ewes (1.3%) required assistance at parturition. None of the sampled ewes was subclinically deficient in calcium or magnesium. Conclusions The study indicates lamb survival was not reduced by grazing oats for an extended period throughout late pregnancy and lambing. Further research is required to determine whether the recorded reduction in lamb survival from grazing oats only during lambing occurs consistently. Implications Ewes may safely graze oat forage throughout late pregnancy and lambing when offered a calcium, magnesium and salt supplement, without this increasing perinatal lamb mortality relative to a legume-based pasture, but there may be a penalty in lamb growth rates and loss of ewe condition, and lamb survival may be reduced with an abrupt change to oats for the lambing period.

Lamb survival and weight at marking may be reduced in ewes lambing on forage oats after grazing lucerne during late pregnancy

Robertson,

Morton,

Friend

et al. 2024

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Including magnesium sulfate in the diet of twin-bearing ewes in the last week of gestation improves the adaptation of lambs to extrauterine life

Minteguiaga,

López Mazz,

Fierro

et al. 2024

Context Most deaths of lambs in the first days of life are due to failure to adapt to extrauterine life. Aims This study aimed to test the hypothesis that adding magnesium sulfate (MgSO4) to the diet of twin-bearing ewes in the last week of gestation improves the adaptation to the extrauterine life of the lambs. Methods Eighty-three multiparous Finnish × Polwarth ewes carrying twins in the last week of gestation were MgSO4 supplemented (n = 40) or allocated to control (n = 43). We recorded the durations of gestation, expulsion and lambing, interlambing interval, and birthweights, meconium score, lamb rectal temperature (at birth and 3 h after birth), whether assistance was needed (yes or no) and time from lamb expulsion to stand and to suck (n = 148). A jugular blood sample of the lambs was analysed for acidity, partial pressures of CO2 and oxygen; active and standard HCO3, blood base excess (BE b) and extracellular fluid base excess (BE ecf), saturated oxygen, and total CO2 concentration. Glucose was analysed with a portable device. Key results Gestation was longer in supplemented ewes (147.7 ± 2.0 vs control: 146.7 ± 1.7 days, P < 0.05). Birthweight and litter birthweight of lambs were higher when ewes were supplemented (3.74 ± 0.6 and 7.47 ± 0.9 kg vs control: 3.51 ± 0.5 and 7.02 ± 0.9 kg, P < 0.05). The need for assistance, meconium score, durations of expulsion and lambing, and time to stand and to suck were not different between treatments (P > 0.05). The interlambing interval was shorter in the supplemented ewes (6.7 ± 2.7 m vs control: 10.4 ± 2.6, P < 0.05). Lamb rectal temperature was not different between treatments 3 h after birth, but at birth was lower in lambs of supplemented ewes (P < 0.05). Treatments did not differ in blood acidity, CO2 partial pressure and total concentration, active and standard HCO3, both measures of base excess, nor blood glucose. Lambs of supplemented ewes had higher oxygen saturation and partial pressure (P < 0.05). Conclusions The MgSO4 supplementation improves the adaptation to extrauterine life in pen conditions. Implications It should be tested whether maternal supplementation with MgSO4 reduces the mortality of twin lambs.

Perinatal lamb survival was not reduced by grazing forage oats

Robertson,

Friend,

Allworth

et al. 2024

Context 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. Aims 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. Methods 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. Key results 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). Conclusions 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. Implications 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.