Macro- and micromineral composition of fetal pigs and their accretion rates during fetal development

Twenty-six crossbreed (Yorkshire x Landrace) sows bred to Duroc boars were used to determine fetal measurements and mineral compositions at various stages of gestation. Sows were fed a vitamin and mineral fortified 15% CP corn soybean meal gestation diet fed at 2.1 kg daily with dietary minerals meeting or in excess of NRC requirements. Sow and litter measurements were evaluated at 5 periods postcoitum (45, 62, 80, 100, 115 d). The experiment was conducted as a completely randomized design with 3 to 6 observations per mean. Uterine fluid and fetal tissue were collected upon slaughter from the sows during the first 4 measurement periods. The empty uterus and uterine fluid contents were weighed. Individual fetuses were weighed and their length measured. Neonatal pigs from 6 sows were killed by electric shock before colostrum consumption. The fetuses and neonates were subsequently frozen, ground, and analyzed for water, protein, ash, and fat. The mineral profile was determined for the entire litter by inductively coupled plasma analysis technology. The sow and litter was each considered the experimental unit for all measurements and mineral compositions with regression analysis determined from 45 to 115 d of gestation. Results demonstrated that fetal weight increased quadratically (P < 0.01) and uterine fluid increased quadratically (P < 0.01) from 45 to 62 d, but then declined to 100 d postcoitum. The water, protein, ash, and lipid content of the fetus increased quadratically (P < 0.01) from 45 to 115 d of development, with the greatest increase of each component occurring during the last 15 d of development. Each of the macro- and microminerals increased curvilinearly (P < 0.01) as fetal development progressed with approximately 50% of the total litter and fetal macro- and micromineral contents occurring during the last 15 d of gestation. These results indicate that there is a large increase in mineral contents of fetal pigs during late gestation and that there may be an increasing sow mineral requirement particularly with high-producing sows having larger litter sizes. Regression equations developed on an individual fetus basis for each macro- and micromineral from 45 d postcoitum to parturition could be used to model mineral accretions.