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 (means +/- 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.(ABSTRACT TRUNCATED AT 250 WORDS)