Perinatal complications and maximising lamb survival in an adolescent paradigm characterised by premature delivery and low birthweight

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.

The genetic and phenotypic associations between lamb survival outcomes and other traits recorded at lambing

“…Adverse relationships between short GL and progenysurvival outcomes have been reported previously for beef cattle (Bunter et al 2014), sheep (Wallace et al 2021) and pigs (Rydhmer et al 2008), where both low BWT and lack of maturity at birth associated with short GL are both problematical for progeny survival. However, the effect of short GL is difficult to avoid in practice, or select against, unless data exist more widely to evaluate genetic differences within progeny of sires for GL.…”

The impact of environmental temperature on ewe reproduction, adaptive responses during insemination, and productive characteristics of the lambs obtained from them

“…This enabled them during almost the entire period of rearing until weaning to have a higher intensity of growth and to achieve a higher live weight at the age of 90 days by 20.1% (P < 0.01) and 26.8% (P < 0.01) for rams and by 19.1% (P < 0.01) and 18.8% (Р < 0.01) for ewe lambs whose mothers were inseminated in the middle and at the end of the mating season. The dependence of the live weight of young animals on the periods of the mating campaign is emphasized in the work (Martínez-Paredes et al, 2018;Wallace et al, 2021). The higher intensity of growth of young animals born from mothers inseminated at the beginning and in the middle of the mating season was consistent with fluctuations in clinical indicators, but they did not have reliable intergroup and seasonal differences and were within the physiological norm.…”

Features of the formation of lambs' adaptive capacity in the first day of life

“…It is well known that the viability of newborn animals and the formation of their clinical status in the initial period of postnatal development act as marker indicators in the activation of thermoregulatory processes, the biological meaning and character of which is to maintain the relative constancy of the organism and release heat under the adverse effects of the environment (Aleksiev et al, 2007;Wallace et al, 2021). In this period, when the functional features of the newborn animal are not yet clearly manifested, the formation of thermoregulatory, cardiovascular, respiratory, metabolic and homeostatic mechanisms are completed, which requires an adaptation period (Piccione et al, 2007;Dwyer, 2008b).…”