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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 behavior

D. R. Miller^*, D. Blache^#, R. B. Jackson, E. F. Downie^* and J. R. Roche^*

^* Tasmanian Institute of Agricultural Research, University of Tasmania,Mt Pleasant, Tasmania, 7250, Australia , ^# School of Animal Biology, University of Western Australia, Crawley, Western Australia, 6009, Australia Department of Primary Industries Parks, Water and Environment, Mt Pleasant, Tasmania, 7250, Australia

Dale.Miller{at}dpipwe.tas.gov.au

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 parameters 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 following 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 lower chill indices at birth, singleton litter status, greater pre-suckling rectal temperature, increasing ewe pre-lambing plasma ghrelin concentration, female sex, heavier birth weight, and lower lamb pre-suckling plasma glucose concentrations. 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. Pre-suckling glucose concentrations were greater in singletons and lambs born to ewes of high BCS at d 95 of gestation, and lambs of heavier birth weight, but were also associated with lower rectal temperatures. This might reflect a delay in glucose utilisation during the adjustment from a fetal metabolic rate to a level appropriate for cold external environments. Singleton lambs exhibited lower pre-suckling 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 high plasma glucose and leptin concentrations prior to lambing, and was positively related to ewe BW at d 95 of gestation and to length of gestation. Greater pre-suckling plasma ghrelin and leptin concentrations were measured for shorter gestation lengths. Neonate pre-suckling 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 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.

Key Words: behavior • ghrelin • neonate • sheep • survival