Abstract
The competition for nutrients in overnourished and still-growing adolescent sheep negatively impacts gestation length, colostrum supply and lamb birthweight, all of which may affect neonatal morbidity and survival to weaning. Herein perinatal complications and the requirement for supplementary feeding were analysed in relation to gestational-intake, and the degree of premature delivery and prenatal growth-restriction exhibited. Pregnancies were established by embryo transfer and the mean/standard deviation (SD) gestation length and birthweight of the optimally-fed control group (n = 100) was used to define early delivery and reduced birthweight categories (1.5 and 3.0 SDs below the control mean for each aspect). Control lambs were largely delivered at term (94%), and had a normal birthweight (92%), while very preterm (≤139days, 18.5%) and preterm delivery (140-142days, 54.8%), extremely low birthweight (ELBW; females ≤2838g and males ≤3216g, 21.1%) and low birthweight (LBW; females 2839 to ≤4001g and males 3217 to ≤4372g, 32.2%), were common in the overnourished group (n = 270, P<0.001). Accordingly, overnourished dams were more likely to lamb without assistance while the incidence of major dystocia was greater in controls. Initial lamb vigour at birth was independent of gestational-intake, delivery or birthweight category but both ELBW and very premature lambs required more assistance with feeding in the first 24h postnatal, primarily reflecting low colostrum availability. Indeed, relative to normal, ELBW lambs had a greater risk of experiencing mismothering, and enhanced likelihood of requiring supplementary feeding throughout the neonatal period (P<0.001). ELBW lambs also had a greater possibility of respiratory issues at birth (P<0.01) and renal complications (P<0.001), while very preterm delivery was associated with an increased risk of gastrointestinal tract problems (P<0.01). In spite of these complications, all-cause mortality was low (5.4%) suggesting that our proactive neonatal care regime can overcome many of the issues associated with extreme prematurity and low birthweight.
Highlights
Pre-weaning lamb morbidity and mortality limits the reproductive output and profitability of sheep farming and is a serious welfare concern
Ninety four percent of control lambs spontaneously delivered at Perinatal complications after adolescent pregnancy term and 92% of lambs had a normal or higher birthweight using the definitions detailed in the methods section
Average gestation length was four days shorter in the overnourished pregnancies (Table 1) reflecting a very high incidence of preterm (54.8%) and very preterm delivery (18.5%), with viable lambs born at day 135 of gestation forwards
Summary
Pre-weaning lamb morbidity and mortality limits the reproductive output and profitability of sheep farming and is a serious welfare concern. The majority of deaths occur in the first three days postpartum and reflect both parturition-related and neonatal losses [2,3,4]. The former primarily include stillbirths, dystocia, birth injuries, and starvation-mismothering while low birthweight, litter size, male sex and primiparity are well-established risk factors for neonatal mortality [1, 5,6,7,8,9,10]. The limited information available for well managed flocks (n = 1077 pregnancies) following spontaneous parturition [12] suggests that preterm delivery equivalent to a 2.5% to 5% reduction in gestation length (140–143 days) is associated with an 15% increase in mortality above that of lambs delivered at term (10%, 144–150 days). In the small number of lambs delivered at 137–139 days, mortality was 90% indicating that sheep do not tolerate early delivery well
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