GROWTH OF THE FETAL GUINEA PIG: PHYSICAL AND CHEMICAL CHARACTERISTICS

Abstract

Achievement of the intrauterine growth rate is a goal frequently used in nutrition of preterm infants. Data on the chemical composition of the human are limited and there is curiously little similar data in experimental animals. We studied physical and chemical macronutrient accretion in the fetal guinea pig, a species in which the high fat content and rapid growth rate emphasize the demands of fetal growth upon maternal nutrition. We studied 32 fetuses in 12 litters ranging from 39 days to term (67 d), analyzing the fetuses for wet weight, dry weight, carbon, nitrogen, fat content, caloric content (bomb calorimeter) and amino acid composition. Body weight increased exponentially with gestational age at 7.1%/d. Dry weight concentration tripled from 10% to 30% by term and total dry weight increased at 10.1%/d. Fat concentration rose from 2% at 45 days to 12% at term and fat content increased 13.5%/d. The total caloric accretion rate was 100 kcal/kg/d at 45 days, increasing to 220 kcal/kg/d at term. Over 60% of the caloric accretion was due to fat accretion. Caloric values of fat and non-fat dry weight were 9.5 and 4.5 kcal/g respectively. Amino acids represented 80% of the total body nitrogen and 46% of the total body carbon. These data represent the first systematic study of chemical growth during fetal life in any experimental animal, provide accretion measurements unavailable in human studies and demonstrate the importance of fat accretion in caloric demands of fetal growth.