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Effect of Zinc Repletion Late in Gestation on Parturition in the Zinc-deficient Rat

U. S. Plant, Soil and Nutrition Laboratory, Northeast Region, Agricultural Research Service, U. S. Department of Agriculture, Tower Road, Ithaca, New York 14850

Parturition can be extremely stressful in rats given a low zinc diet from day 1 of pregnancy. Experiments were done to determine how late in gestation zinc could be given to the female and result in normal parturition. A low zinc diet (<1 ppm) was given adult females beginning day 1 of pregnancy. Late in pregnancy a single dose of either 15 or 30 mg zinc acetate was given by stomach tube. In one experiment females had access to 100 ppm zinc in the drinking water subsequent to stomach tubing. Females were killed 6 hours after the birth of the first pup; and organ weights, tissue zinc concentrations, and adrenal cholesterol were determined. Repletion with zinc on day 15, 18, or 19 resulted in essentially normal parturition although many of the females given zinc day 18 or 19 eventually ate the pups. Administration of zinc on day 20 or 21 enabled some, but not all, of the females to deliver reasonably normally. Females given zinc on day 22 were as stressed as the zinc-deficient controls. Concentrations of zinc in maternal liver and in the pup were generally higher the later repletion was begun. Serum and liver zinc levels after parturition in females given a single dose of zinc on day 18 were not significantly different from the zinc-deficient females. These experiments indicate that the critical time for administering zinc in order to prevent stressful parturition in the zinc-deficient rat is between day 19 and 21.

KEY WORDS: • zinc • zinc deficiency • gestation • pregnancy • parturition

Manuscript received 13 December 1972.