Metabolic maturity at birth and neonate lamb survival: Association among maternal factors, litter size, lamb birth weight, and plasma metabolic and endocrine factors on survival and behavior1

Abstract

This paper reports an investigation into metabolic and endocrine maturity in the neonate lamb and the relationships between litter size, birth weight, and maternal metabolic and endocrine variables on behavior at birth and survival over the first 72 h of life. Data were from multiparous, fine-wool Merino ewes (n = 150; equal numbers of single-lamb and twin-lamb bearing status) lambed on pasture after late gestational glucocorticoid treatments. Stepwise multiple regression analysis was used to investigate relationships between lamb survival, behavior, endocrinology, and physiology. Improved lamb viability at 72 h after birth was related to decreased chill indices at birth, singleton litter status, greater presuckling rectal temperature, increased ewe prelambing plasma ghrelin concentration, female sex, heavier birth weight, and decreased lamb presuckling plasma glucose concentration. Greater rectal temperatures were associated with heavier birth weight and gestation lengths shorter than 146 d, but no relationship with neonatal behavioral progression was evident. Presuckling glucose concentrations were greater in singletons and lambs born to ewes of greater BCS at d 95 of gestation, and lambs of heavier birth weight, but were also associated with decreased rectal temperatures. This might reflect a delay in glucose utilization during the adjustment from a fetal metabolic rate to a rate appropriate for cold external environments. Singleton lambs exhibited decreased presuckling plasma NEFA concentrations and were almost 8 times more likely to survive to 72 h than a twin-born lamb. Birth weight was lesser in lambs born to ewes with elevated plasma glucose and leptin concentrations before lambing and was positively related to ewe BW at d 95 of gestation and to length of gestation. Greater presuckling plasma ghrelin and leptin concentrations were measured for shorter gestation lengths. Neonate presuckling ghrelin concentrations above 650 pg/mL tended (P = 0.077) to be associated with improved lamb survival to 72 h. This was consistent with a curvilinear decline in neonate survival rates to 72 h after birth as time of latency to suckle increased. No relationship was observed between lamb plasma glucose concentrations and behavioral expression after lambing. Lambs exhibiting greater metabolic and endocrine maturity at birth had improved survival in a cold environment to 72 h after birth. The role of ghrelin in ovine fetal development warrants further investigation.

Supplementation of Merino ewes with cholecalciferol in late pregnancy improves the vitamin D status of ewes and lambs at birth but is not correlated with an improvement in immune function in lambs

“…Furthermore, the birthweights of the lambs were close to the range of 4.5-5.5 kg, at which maximum survival occurs, and the rectal temperatures and blood glucose concentrations at birth were similar to those reported previously, therefore indicating that the lambs were not at an increased risk of death in the first 72 h of life (Stafford et al 2007;Miller et al 2010;Chniter et al 2013). On average, only 4.6% of lambs born alive died within the first 72 h of life in the present study, which is considerably lower than the expected mortality of 20-30% (Oldham et al 2011;Hawken et al 2012;Hinch and Brien 2014).…”

“…On average, 30% of all lambs born will die before weaning, and ~80% of lamb deaths occur in the first 48-72 h of life (Miller et al 2010;Oldham et al 2011;Hawken et al 2012;Hinch and Brien 2014;Paganoni et al 2014). Lamb birthweight is the greatest contributor to lamb survival and is strongly influenced by ewe nutrition during pregnancy (Oldham et al 2011;Paganoni et al 2014).…”

Time trends and epidemiological patterns of perinatal lamb mortality in Norway

“…Several studies have shown that in flocks managed permanently outdoors, harsher conditions in terms of low temperatures, wind and precipitation decrease early neonatal lamb survival [ 10 , 29 , 31 ]. With very few exceptions, lambing takes place indoors in flocks in Norway, which should be expected to prevent neonatal deaths caused by adverse weather conditions.…”

Invited review: Improving neonatal survival in small ruminants: science into practice

“…Improved lamb viability beyond 72 h is associated with decreased vulnerability to chilling, singleton status, higher pre-suckling body temperature, decreased pre-suckling glucose concentrations, high plasma concentration of proteins, lipids and immunoglobulins, and a moderate rise in neonatal cortisol concentration (Eales et al, 1982;Miller et al, 2010). Being bigger is an advantage in terms of vigour and thermoregulation, as lambs are more efficient in their suckling activity and in resisting cold exposure.…”