Maternal-Fetal Utilization of Sulfate Sulfur by the Gravid Ewe

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Abstract
Blood-balance and maternal-fetal tissue concentration values, following single tracer doses of 35SO4, were used to evaluate sulfate absorption and utilization in 25 yearling gravid ewes and fetuses at 3 periods of gestation. The 81% dietary sulfur excreted was almost equally divided between feces and urine. Ingested labeled sulfate, however, was rapidly absorbed, and 75% was subsequently excreted via the kidneys during 168 hours. Maternal tissue sulfur concentration was unaffected by pregnancy, but retained 35S was significantly higher (P < 0.10) at trimesters 1 and 2 in 45-kg ewes. Absorbed 35S traversed the placenta freely at the 3 trimesters, and maternal-fetal tissue concentration patterns, after 7 days, were similar. Soft tissue 35S levels in third-trimester ewes peaked after 4 hours, and decreased to 168 hours. Values for most bones and placenta were highest after 24 hours, and levels decreased to 7 days. Calculated partition of 35S in third-trimester ewes and products of conception indicated that after 7 days, 55.7% of that absorbed and retained was deposited in maternal tissues, and 44.3% was transferred to the total fetus (77%), the placenta (16%) and to the placental fluids (7%), respectively.