A closer look at the efficiency of different zinc sources By Dr. Bastian Hildebrand, Biochem Zusatzstoffe GmbH, Germany


The essential requirement of the trace mineral zinc for health and growth of animals is well known. The normal functioning of the immune system, bone mineralisation, growth rate, fertility parameters and the integrity of skin and hoof tissue are all important functions affected by the animal’s zinc status. They are impaired when the animal reaches the limits of its capability to mobilise zinc from the body’s tissues and when zinc absorption from the gastro-intestinal tract (GIT) is inadequate. The latter depends on dietary zinc. For most animals the zinc supply for ensuring normal growth and performance is reported to range between 40–80 mg/ kg diet, including native zinc background levels of feed stuffs. In practice zinc is still supplemented with additional safety margins of 50% or more to compensate for variations in the animal’s individual demand and uncertainties due to nutritional factors impairing zinc absorption. Several factors have been identified that alter zinc availability for


absorption in the GIT, including pH dependent solubility or different forms of antagonisms. For instance, high levels of calcium and phytate, as present in diets for lactating sows or laying hens, depress solubility and hence absorbability of zinc. Or diets containing pharmacological copper levels can induce a secondary zinc deficiency in piglets. Adaptations in diet composition, as well as the use of phytase enzymes and specific zinc compounds, can help to improve zinc absorption. Moreover, environmental concerns over zinc excretion have led to an increase in the search for more efficient and safe zinc additives. Several forms of zinc compounds are commercially available (Table 1). During the last two decades several forms of zinc amino acid


chelates have been introduced to the market. They differ in binding partner, production process, zinc : amino acid ratio, and degree of chelation. Furthermore, application-related properties such as water solubility and particle structure (powder/granule) vary between sources.


However, differences in the physical and chemical properties of zinc sources do not accurately predict zinc bioavailability.


Evaluation of different zinc sources In order to compare the efficiency of zinc compounds in supporting animals’ zinc status, measurements of absorption and retention provide the most valuable information. However, respective in vivo comparisons of different organic Zn sources are scarce. A depletion - repletion study was conducted at University of Berlin, Germany, in order to investigate the effects of different zinc sources on apparent zinc digestibility in piglets, commonly used as an animal model for trace mineral studies. A group of 72 early-weaned piglets were fed a basal diet with only native contents of zinc during a 14-day depletion period from day 25 to 38 of age. In the following repletion period, from day 39 to 47 of age, animals were distributed to 6 feeding groups: a negative control (Basal) without Zn supplementation; two positive control groups with Zn sulfate (Zn-SUL) or tetra-basic zinc chloride (TBZC); and three treatment groups with zinc bound to amino acids from soy protein (Zn-AAC), bound to hydroxy analogue of methionine (Zn-MHA), or to synthetic glycine (Zn-GLY, E.C.O.Trace®


Zn). Zinc concentration of


the tested products Zn-SUL, TBZC, Zn-ACC, Zn-MHA, and Zn-GLY was 35%, 54%, 10%, 17.5%, and 27%, respectively. Zinc was added at 30 mg per kg diet to cover piglet’s requirements (GfE, 2006) in the presence of 170 ppm dietary copper sulfate levels, as typically used in most piglet diets. Apparent zinc digestibility was measured by marker method (TiO2


) during day 45 and 47 of age (Figure 1). As expected, the analysis of fecal samples from 12 piglets per


feeding group showed that apparent zinc digestibility of the total diet was significantly increased by the use of zinc additives compared to


Table 1: Zinc additives according to European Union Register of Feed Additives, Edition 4/2018 (modified).


Zinc additive (EU identification No.) Zinc acetate dihydrate (3b601) Zinc chloride anhydrous (3b602) Zinc oxide (3b603)


Zinc sulphate, heptahydrate (3b604) Zinc sulphate, monohydrate (3b605)


Zinc chloride hydroxide monohydrate (3b609); Synonym: TBZC


Zinc chelate of amino acids hydrate (3b606) Zinc chelate of glycine hydrate, solid (3b607)


Zinc chelate of hydroxy analogue of methionine (3b610)


Zinc chelate of methionine (1:2) (3b611) Zinc chelate of protein hydrolysates (3b612)


Zinc bislysinate (3b613) PAGE 30 NOVEMBER/DECEMBER 2018 FEED COMPOUNDER Zn(x)1-3 · nH2 Zn(x)1-3 · nH2 Zn(x)1-3 Zn(CH3


Chemical formula COO)2


ZnCl2 ZnO


Zn5


ZnSO4 ZnSO4 (OH)8


· 7H2 · H2


Cl2 O O · H2 O


O, x= anion of any amino acid from soya protein hydrolysate


· nH2


O, x= anion of glycine Zn-(HMTBa)2


C10 H20 N2 O4 S2 Zn


O, x= anion of protein hydrolysates containing any amino acid from soya protein hydrolysate


Zn(C6 H13 N2 O2 )2 · 2HCl · 2H2 O · 2H2 O


Min. Zinc (%) ≥ 29.6 ≥ 46.1 ≥ 72.0 ≥ 22.0 ≥ 34.0 ≥ 54.0


≥ 10.0


≥ 15.0 ≥ 17.5


≥ 17.5 ≥ 10.0


≥ 13.5


Chelated


Inorganic


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