Changes in body composition of pig fetuses during pregnancy

40 fetuses taken from 10 litters on day 50, 60 fetuses taken from 15 litters on day 105 of the respective pregnancies and 6 newly born piglets taken from 3 litters were analyzed for dry matter, total N, amino acids, fat, energy and 5 major minerals. As compared to the amounts found at birth, on day 50 about 3 per cent of the Na and K and less than 2 per cent of the other components were found. On day 105th the corresponding percentages were 96 and 95 for Mg and K, 88 and 86 for fat and Na, between 71 and 74 for dry matter, N, energy and P, and 63 for Ca. During the course of pregnancy proportions of alanine tyrosine, phenylalanine and lysine decreased, whereas those of proline and glycine increased. From the information presented in tables 4 and 5 it may be concluded that most of the fetal gain or organic and inorganic matter takes place during the last part of pregnancy. Increased nutrient requirements of the dam should be of quantitative importance only during this relatively short period. Changes in concentrations of protein and mineral elements during the course of pregnancy are not proportional.