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Gestation Age Effects upon Maternal-Fetal Zinc Utilization in the Bovine¹

Louisiana Agricultural Experiment Station, Baton Rouge, Louisiana

Abstract

Twenty-four gravid cross-bred heifers were maintained on conventional cottonseed hull, corn, soybean meal rations and killed at 90, 180 or 270 days gestation for maternal fetal tissue analyses. Fifteen of these heifers were dosed orally or intravenously with Zn⁶⁵ for 24, 96 or 168 hr. blood-balance study previous to sacrifice. Cows consuming 28 ppm zinc absorbed 22±5%, excreted 4.3±0.4 mg./day in the urine and transferred 5.8 mg. zinc to the fetus during the first 90 days of pregnancy. Fetal zinc increased 13 times between trimester 1 and 2 and another 7 times during the final trimester. Pregnancy effects were not observed either on blood or fecal excretion patterns nor upon maternal tissue zinc concentration values. Both total and absorbed radiozinc were highest in liver, pancreas, muscle, kidney, spleen and adrenal, in that order for soft tissue. Zinc concentrations in ribs, femur and mandible equaled that for liver. Maternal tissue Zn⁶⁵ levels, after 168 hr., showed significant increases at each trimester, and fetal liver and bone Zn⁶⁵ values usually exceeded those of the dam. Maternalfetal tissue Zn⁶⁵ values from cows killed after 24, 96 and 168 hr. after intravenous dosing showed deposited maternal liver Zn⁶⁵ to decrease markedly at each period, while fetal liver and bone values tripled. Calculated partition of radiozinc in third trimester cows and products of conception indicated that after seven days 86.3% of that Zn⁶⁵ absorbed was retained by the dam, and 13.7% was transferred and deposited in the total fetus (58.7) placenta (40.9) and fluids (0.4).

¹ Published with the approval of the Director, Louisiana Agricultural Experiment Station, Baton Rouge. Grateful appreciation is expressed to T. O. McRae for breeding and care of the gravid heifers; to Sharon Nicholson and J. E. Klawinski for technical assistance and to the National Science Foundation (Contract GE 6602) for partial support of this study.

² Present address: Animal Science Department, University of Tennessee, Knoxville 37916.