Influence of relative size at birth on growth and glucose homeostasis in twin lambs during juvenile life

The effect of differences in size at birth on growth and glucose homeostasi s between female twin lambs during juvenile life was examined. Twenty-six s ets of twins were entered into the study, of which ten mere used for organ sampling at birth and 16 were studied over the first year of life. Eleven s ets were defined as being mismatched for birthweight as the weight differen ce between twins was >25%, with light lambs weighing 4.1 +/- 0.3 kg and hea vy lambs weighing 5.1 +/- 0.1 kg. All remaining twins were matched in bodyw eight, weighing 4.6 +/- 0.5 kg, During the rapid period of juvenile growth (i.e. one, three and six months of age) and following stabilization of body weight (i.e. 12 months of age) glucose tolerance tests were performed by in travenously injecting 0.8 mg kg(-1) bodyweight glucose. This was followed t he next day with an insulin tolerance test, performed by intravenously inje cting 0.08 units kg I bodyweight insulin. At birth there were no difference s in organ weight as a fraction of total bodyweight between matched and mis matched twins, but the ratio of liver to brain weight was lower in light co mpared with heavy twins. Light lambs remained lighter than their twins up t o six months of age, and crown-rump length was also shorter. At one and thr ee months of age there were no differences in basal plasma glucose concentr ations between the groups, but glucose tolerance was greater in light compa red with heavy lambs at one and six months of age. Insulin tolerance was gr eater in light compared with matched lambs at one and six months of age. In conclusion, it has been shown that size at birth of one twin in relation t o its co-twin is one factor determining glucose regulation during postnatal life. This not only affects glucose and insulin tolerance but also growth over the first six months of age.