Body weight distribution and organ size in newborn swine (sus scrofa domestica) -- a study describing an animal model for asymmetrical intrauterine growth retardation

Abstract

Normal growth is the expression of the genetic potential to growth which is neither abnormally constrained nor promoted by internal or external factors. Restricted fetal growth is common in human pregnancy and is associated with increased perinatal morbidity and mortality. Because of ethical restrictions, pathogenetical studies are necessarily dependent on appropriate animal models. In the studies presented, evidence will be provided that the naturally occurring distribution of body weight in newborn piglets, obtained from n = 512 newborn piglets (about 12 hours old) in 50 consecutive deliveries in the breed cohort of the mixed German domestic breed - "Deutsches Land-/Edelschwein" gives an appropriate sampling for providing a statistically reliable basis with which to determine different degrees of fetal growth for further pathophysiological studies intended. A strong inverse correlation (r = -0.66, p < 0.05) was found between the mean weight of the litter and the number of piglets per litter, and an inverse correlation (r = -0.64, p < 0.05) was found between the lowest weight of the littermate and the number of piglets per litter. Moreover, gravimetric investigations were made into an additional 53 one-day-old newborn piglets reflecting the naturally occurring birth weight distribution determined. A marked linear correlation between body weights and various organ weights was found (values of the correlation coefficient amounted to between 0.45 and 0.98; p < 0.05). The lowest variation of organ weights was found in the CNS structures (0.68-1.33). Skeleton and heart exhibited similar ranges of weight variation (0.35-1.81 and 0.38-2.00 of the means) to body weight (0.38-1.77 of the means). This was also expressed in the regression analysis, because the slope values were 0.99 and 0.97 respectively. The hormonal glands investigated, the kidneys, and the abdominal parenchymal organs exhibited the largest ranges of weight variation. Moreover, regression analysis gives evidence that the weight restriction was more pronounced than expected concerning respective body weight. This is indicated by slope values > 1 in almost all of those organs. Plasma concentration of IGF-1 showed an inverse correlation with body weight (r = -0.42; p < 0.05, fig 4). IGF-1 concentration of intrauterine growth retarded (IUGR) newborn piglets was in the mean nearly double that of normal weight animals (p < 0.05) and the brain weight to liver weight ratio was increased more than 2.5 times in IUGR newborn (fig 5 A, p < 0.05). This investigation provides information on the naturally occurring body weight distribution of one-day-old piglets, which was obviously a result of epigenetic factors. Gravimetrical estimation showed clearly that body weight variety is most probably caused by alterations of placental functioning. Severe alterations resulted in asymmetrical growth retardation, which was proved by a significantly increased brain to liver ratio in animals with a body weight < 10th centile. Thus, evidence is provided that naturally occurring asymmetrical intrauterine growth restricted newborn piglets can be identified simply by body weight measurement, so that convenient conditions are given for pathogenetically motivated studies on intrauterine compromised newborns.