New Evidence that the Intra-Uterine Growth-Retarded Piglet Is a Member of a Discrete Subpopulation

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Abstract
The statistical distribution of birth weights in 54 litters of piglets was examined in an attempt to identify intra-uterine growth-retarded animals. Although birthweight distribution was normal in some litters, in others there appeared to be a discrete subpopulation of 1 or more growth-retarded animals. Inspection of published data from the rat and mouse suggests that a similar phenomenon occurs in other polytocous species. These findings imply that growth-retarded neonates of these and possibly other species should not be regarded as the tail-end of a normal distribution, but that they are the result of some distinct process occurring during gestation.