Forced resting by high dietary zinc: tissue zinc accumulation and reproductive organ weight changes [Laying hens]

An experiment was conducted to investigate the effects of high dietary zinc, as a means of inducing a forced-rest, on selected organ accumulation of zinc and reproductive function in terms of ovary and oviduct weight in the laying hen. Single Comb White Leghorn hens laying approximately at 60% production were fed either 10,000 ppm zinc as zinc oxide (10 Zn) or 20,000 ppm zinc (20 Zn) for a period of 4 days. At the initiation of the experiment (Day 0), five hens were killed and organs obtained for analysis. On 4, 10, 16, and 22 days afterward, similar samples were obtained from 5 hens per treatment. Ovary and oviduct weights were determined and zinc analysis performed on the latter as well as liver, kidney, and pancreas. The brief 4-day feeding of either high zinc diet caused a marked 80% reduction in ovary weight by Day 10. The oviduct, although less affected, was still reduced approximately 60% in weight after feeding either 10 Zn or 20 Zn for 4 days. The oviduct exhibited a statistically significant elevation in zinc concentration on Day 4 but was normal by Day 10 (6 days following the refeeding of a normal diet) and not different between treatments. There was extensive accumulation of zinc in kidney, liver, and especially pancreas after 4 days of feeding either 10 Zn or 20 Zn. The level of dietary zinc had no effect on the extent of accumulation in any tissue. The depletion of tissue zinc roughly corresponded to the magnitude of increase in the concentration of zinc observed at Day 4. Possible ramifications of the dramatic increase observed in pancreatic zinc were discussed. We concluded that feeding either 10 Zn or 20 Zn as a means of inducing a forced rest effects a marked and rapid reduction in ovary and oviduct weight as well as an extensive increase in renal, hepatic, and especially pancreatic zinc.