Relationships between plasma concentrations of placental lactogen, insulin-like growth factors, metabolites and lamb size in late gestation ewes subject to nutritional supplementation and in their lambs at birth

Abstract

The relationships between placental lactogen (PL), insulin-like growth factor (IGF) -1 and -2, insulin, glucose and nonesterified fatty acids (NEFA) were studied in 10 triplet-bearing ewes in late gestation (120-129 days) which were on ad libitum feeding. To extend the range of plasma metabolite concentrations the ewes received a continuous abomasal infusion from 100 days of gestation until delivery. Three were infused with glucose (160 g/day), 2 received sodium caseinate and 3 were infused with control fluid alone. From 120 days the animals were fed 3 hourly intervals from a belt feeder to achieve steady state and at 125-130 days had intravenous plasma samples pooled for analysis. There was no effect of nutritional supplementation on birth weight. Casein supplementation was associated with reduced maternal PL concentrations but glucose supplementation had no effect on PL concentrations. Circulating PL concentrations showed a positive correlation to IGF-2 activity (r = 0.64, P less than 0.05) and a negative relation to IGF-1 concentrations (r = -0.73, P less than 0.05). IGF-1 levels were higher (P less than 0.05) and IGF-2 levels were lower (P less than 0.05) in nutritionally supplemented ewes. In the ewe, NEFA concentrations showed a negative relationship to IGF-1 (r = -0.75, P less than 0.05) and a positive relationship with IGF-2 (r = 0.87, P less than 0.1). Similar relationships were observed in the ewe at term. These observations suggest that nutritional factors and PL may be important determinants of IGF-2 secretion in the late-gestation ewe. They suggest the possibility that IGF-2 mediates the lipolytic effects of PL.(ABSTRACT TRUNCATED AT 250 WORDS)