At Alltech's recent 25th International Animal Health and Nutrition Symposium Dr. Sheila Scheideler, a professor at the University of Nebraska, presented on a series of trials on trace mineral supplementation in relation to productivity of flocks and quality of eggs.
It is axiomatic that bioplexed and chelated minerals have a higher rate of absorption than the inorganic analogues. The important question is whether the incremental cost for these products is justified given the low cost of manganese, iron, copper and zinc supplements. The specific requirements of flocks to achieve optimal egg quality may be influenced by local farm factors such as mineral content, pH and hardness of water. It is also evident that the requirements of caged flocks which are held on galvanized wire and floor flocks which practice coprophagy may be different.
In relation to shell quality, zinc, which is a co-factor of carbonic anhydrase, is involved in mineralization. Manganese is a component of mucopolysaccharides.
Shell membranes could decline in quality if a deficiency occurs in diets of laying flocks. Attempts at evaluating the economic return from bioplexed minerals have not shown any quantifiable benefits on production parameters although some studies have shown significant improvement in shell quality. With regard to selenium, there is clear evidence that integrity of the vitelline membrane of the yolk is increased in comparison to eggs produced by hens which are feed diets either low in selenium or containing selenium derived only from sodium selenite.
Dr. Scheideler presented data demonstrating that breaking strength of shells was improved from 27 to 29 Newtons and cracked eggs were reduced from 0.96% to 0.70% and that carbonic anhydrase content of the oviduct was increased significantly from 150 to 200 units/gram of tissue over the 40-week production period beginning at 20 weeks.
Whether these small differences can translate into financial return was not considered in her paper. Synergistic effects from supplementing diets with both vitamin E and organic selenium were shown although there is some concern that elevating selenium intake may depress vitamin E content of eggs (Renema’s Studies in Alberta).
An incidental observation on timing of supplementation of diets with bioplexed minerals suggest that contrary to intuitive reasoning, it is more beneficial to feed these supplements during the first third of the cycle although continual feeding appears advantageous. Copper and iron are adequate in corn-soy diets using ingredients derived from the Midwest and no additional supplementation of these elemental nutrients is necessary.
Based on the review of data our decision to incorporate two-thirds of selenium in the form of selenomethionine is justified. The claimed 2% improvement in production is probably spurious and will not be achieved or be quantifiable under commercial conditions. Obviously providing selenium in the organic form increases selenium content of the yolk (0.63 to 0.75 micrograms/gram of yolk).