High Dietary Zinc and Fasting as Methods of Forced Resting: A Performance Comparison

A study was conducted to compare fasting and high dietary zinc as procedures to induce a forced rest of laying hens. Five to six replicates (25 hens each) of Single Comb White Leghorn hens laying approximately 60% were fasted for 10 days (fasted) or fed either 10,000 ppm zinc (10 Zn) or 20,000 ppm zinc (20 Zn) for a period of 4 days. A fourth treatment consisted of feeding 20,000 ppm zinc for 8 days (20 Zn-8). During the rest-inducing period, hens consumed little of either high zinc diet. Four-day intake by 20 Zn hens averaged 17.6 ± .2 g/hen/day compared to 32.6 ± 1.5 g/hen/day (X̄ ± SEM) for 10 Zn hens. Those fed 20 Zn-8 consumed the least amount, 12.6 ± .2 g/hen/day during the 8 days of high zinc feeding. Body weight loss of hens in this last group was comparable to hens fasted for 10 days (fasted), i.e., 24.6 ± .3% vs. 27.6 ± .4%. Weight loss of hens in the remaining two groups reflected, to some extent, differences in feed consumption. The 20 Zn hens lost significantly more body weight during the 4-day period when compared with 10 Zn hens (16.2 ± .4% vs. 11.9 ± .5%). Each treatment resulted in a sharp drop in egg production. By the 5th day, fasted, 20 Zn, and 20 Zn-8 hens had ceased producing eggs. Egg production by 10 Zn hens declined at a slightly slower rate. There were considerable differences in post-rest egg production among the various treatments. Although all groups were producing equally in the 6th week of the experiment, peak production (Weeks 9 to 15) was highest in fasted hens (74.9%), lowest (65.5%) in 20 Zn hens and intermediate in 10 Zn hens and 20 Zn-8 hens producing at 70.0 and 71.1%, respectively. Overall, for the 7-month experiment 20 Zn and 20 Zn-8 hens both produced significantly fewer eggs when compared with fasted hens. There was no significant difference between the number of eggs produced by the latter group and those produced by 10 Zn hens. These results suggest that feeding a high zinc diet as a means of inducing a rest offers no advantage over simple fasting.