| Popis: |
The effects of phasing dietary protein and calcium levels on egg weight and shell quality were studied using 1200 White Leghorn hens of four strains housed in group cages. Hens fed diets decreasing in protein by 1% while increasing in calcium by .5% at 12-week intervals had a greater early egg weight combined with a significantly slower rate of increase in egg weight with age than those from the control hens fed a diet with the average protein and calcium contents of the phased diets. Average egg weights for the 48-week trial were identical for both treatments. Shell quality, as measured by shell weight per unit of surface area of the egg (SWUSA), was significantly affected by the calcium level fed. When the dietary calcium level was phased upward, the rate of decline in shell quality, with increasing age of the hen, was significantly slower than with the control diet. Egg production, mortality, and the percentage of uncollectible eggs were not affected by dietary treatment Feed efficiency, as measured by the metabolizable calories required per unit of egg mass, was significantly poorer for the hens fed the phased protein diets than for those fed the diets phased in both protein and calcium. The strain of hen had significant effects on egg production, feed efficiency, egg weight, shell quality, and mortality but not on uncollectible eggs. One of the two midget strains, although housed at 14% greater bird density, had 5 and 10% improved feed efficiency, 2% lower and 1% greater egg weight, and shell quality 6% higher and equal to the two standard-sized strains, respectively, while matching them in egg production. Performance of one midget strain was not up to the overall standard exhibited by the standard-sized birds nor the other midget strain. |
