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

Twenty-six crossbreed (Yorkshire × Landrace) sows bred to Duroc boars were used to de- termine fetal measurements and mineral compositions at various stages of gestation. Sows were fed a vitamin and mineral fortified 15% CP corn soybean meal ges- tation 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 post- coitum (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 tis- sue 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 colos- trum consumption. The fetuses and neonates were sub- sequently frozen, ground, and analyzed for water, pro- tein, ash, and fat. The mineral profile was determined for the entire litter by inductively coupled plasma anal- ysis 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 fe- tal weight increased quadratically (P < 0.01) and uter- ine 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 devel- opment, 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 ap- proximately 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 min- eral requirement particularly with high-producing sows having larger litter sizes. Regression equations devel- oped on an individual fetus basis for each macro- and micromineral from 45 d postcoitum to parturition could be used to model mineral accretions.