Investigation of relative bioavailability values and requirement for Bioplex® organic zinc in broiler chicks

Zinc (Zn) has been known to be an essential nutrient for normal growth and feathering of chicks for half a century (O’Dell and Savage, 1957). The zinc requirement of chicks was first defined to be 30 ppm by Roberson and Schaible (1958). Subsequent research provided evidence for the 1994 Nutrient Requirements for Poultry (NRC, 1994) to set the requirements of broilers at 40 ppm.

However, most of these research data are more than 10 years old and do not represent the needs of modern strains of commercial poultry (Leeson, 2003). On the other hand, organic mineral sources have been used increasingly in recent years due to their higher bioavailability (Wedekind and Baker, 1989; Wedekind et al., 1992; Cao et al., 2000) and lower manure loading.

In general, inconsistency exists among research results regarding bioavailability of organic zinc sources. Some studies (Hill et al., 1986; Pimentel et al., 1991; Ammerman et al., 1995) indicated small or no differences in bioavailability between inorganic and organic zinc sources. The objective of this study was to determine the relative bioavailability value of Bioplex® Zn (a chelated Zn proteinate) comparing with ZnSO4•7H2O (Zn sulfate) for chicks and to determine the requirement of Bioplex® Zn for broiler chicks.


MATERIALS AND METHODS

Two experiments were conducted with one-day-old male chicks from a female broiler breeder line. Chicks were housed in wire mesh-floored pullet starter cages (61 cm x 51 cm x 36 cm) in an environmentally controlled room located at the University of Kentucky’s Coldstream Research Park. Both experiments used a randomized complete block design with blocks based on physical location of the cages within the room. Continuous light (22L:2D) was provided daily. Each cage had one feeder that was covered by plastic and two adjustable nipple drinkers. Chicks were provided ad libitum access to feed and water. The water contained no detectable zinc. A corn-soybean meal basal diet (Table 1) was formulated to be adequate in all nutrients except zinc (NRC, 1994). The assayed zinc concentration in the basal diet was 23 mg/ kg. Zinc was added to the diet at the expense of corn and was provided as analytical grade Zn sulfate (ZnSO4•7H2O) or Bioplex® Zn, which contained 10% Zn and was supplied by Alltech Inc., Nicholasville, KY.



A total of 252 chicks were used in Experiment 1. Chicks were randomly allotted to seven dietary treatments with six replicate cages of six chicks per cage. Treatments consisted of feeding either basal diet, or the basal diet with three supplemental levels of Zn (20, 40 and 80 mg/kg) from Bioplex Zn® or ZnSO4•7H2O. In Experiment 2, dietary additions of Zn included 0, 5, 10, 20 and 40 mg/kg from either Bioplex® Zn or Zn sulfate. A total of 432 chicks were randomly distributed to each of nine dietary treatments with eight replicate cages of six chicks per cage. Both experimental periods were 21 days.

At the end of each experiment, four chicks from each cage (24 chicks per treatment) in Experiment 1 and three chicks from each cage (24 chicks per treatment) in Experiment 2 were killed by asphyxiation with argon gas followed by cervical dislocation. The liver and right tibia were removed and pooled by cage. Livers were homogenized and dry matter content was determined (AOAC, 1995). Bones were boiled, cleaned and dried at 60ºC for 72 h. Bones were defatted using petroleum ether and dry-ashed at 600ºC overnight in a muffle furnace. The liver and bone ash were then microwave-digested with HNO₃ (AOAC, 1995). The zinc concentration of feed and tissue samples was determined by an Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES).

Data were analyzed by ANOVA for a randomized complete block design using the linear model of Statistix V. 8. (2003) (Analytical Software, Tallahassee, FL). Mean differences were determined using Fisher’s least significant difference test. Significance was declared when probability was less than 5%. Linear and quadratic effects were tested using polynomial contrasts. A single-slope broken-line method as described by Robbins (1986) was used to determine break point and slope below the break point.


RESULTS

Growth performance and tissue zinc data collected from Experiment 1 are shown in Table 2. Dietary zinc supplementation significantly increased weight gain (P<0.01). Total tibia zinc increased linearly (P<0.01) with dietary zinc up to 40 ppm. Liver zinc concentration was not influenced by dietary supplementation.
Growth performance and tissue zinc data collected from Experiment 2 are shown in Table 3.

Dietary additions of zinc from either source increased feed intake and liver zinc content (P<0.01). Weight gain increased linearly (P<0.01) with dietary zinc from Bioplex® Zn up to 10 ppm and from zinc sulfate up to 20 ppm (Figure 1). The broken-line analysis of weight gain regressed on supplemented dietary zinc level showed the break point for Bioplex® Zn to be at 6.3 ppm vs. 13.6 ppm for zinc sulfate (Table 4). The supplemental level of 13.6 ppm Zn from zinc sulfate is close to the NRC (1994) requirement of 40 ppm when the basal level of 23 ppm is taken into consideration as a contributor to the total requirement. This result is also consistent with the results reported by Batal et al. (2001). The slope ratio between Bioplex® Zn and ZnSO4 below the break point gave a relative bioavailability 177% for Bioplex® Zn based on weight gain (Table 4). These data are consistent with results reported by Wedekind et al. (1992), who found the relative bioavailability of an organic zinc source to be 177% relative to zinc sulfate.

Table 2. Performance and tissue mineral content of chicks fed Bioplex® Zn or zinc sulfate in a corn/soybean meal diet (Experiment 1)¹.





Table 3. Performance and tissue mineral content of chicks fed Bioplex® Zn or zinc sulfate in a corn/soybean meal diet (Experiment 2)¹.





Dietary supplementation of Bioplex® Zn at 5, 10 and 20 ppm significantly increased total tibia zinc content compared with zinc sulfate (Figure 2). The broken-line analysis of total tibia zinc content regressed on supplemental dietary zinc level showed the break point to be 17.5 ppm for Bioplex® Zn (Table 5). The relative bioavailability of Bioplex® Zn based on the slope ratio of tibia Zn content below the break point was 202% (Table 5). These results agree closely with 206% reported for the bioavailability of zinc from organic zinc source when using tibia Zn content as the response variable (Wedekind et al., 1992).


Figure 1.Linear portion of weight gain regressed on dietary zinc concentration.



Table 4.Broken-line analysis of weight gain regressed on dietary zinc concentration (Experiment 2).









Figure 2. Total tibia zinc regressed on dietary zinc concentration (Experiment 2).





IMPLICATIONS

The results of the present studies indicate differences between zinc sources only at the low level (<20 mg/kg) of added dietary zinc. The bioavailability of Bioplex® Zn is 177% that of zinc sulfate based on the weight gain data, and 202% that of zinc sulfate based on the total tibia zinc content. The zinc requirement of broiler chicks can be met with Bioplex® Zn at 6.3 mg Zn/kg in a corn-soy diet. This new value allows one to meet the zinc requirements of broilers while greatly reducing zinc excretion. As environmental protection laws are enacted around the world, this will be a powerful tool to address environmental concerns while maintaining optimal animal performance.


REFERENCES

AOAC: Official Methods of Analysis.1995. Association of Official Analytical Chemists. Washington, DC.

Ammerman, C.B., D.H. Baker and A.J. Lewis. 1995. Bioavailability of Nutrients for Animals: Amino Acids, Minerals and Vitamins. Academic Press, San Diego, CA.

Batal, A.B, T.M. Parr and D.H. Baker. 2001. Zinc bioavailability in tetrabasic zinc chloride and the dietary zinc requirement of young chicks fed a soy concentrate diet. Poult. Sci. 80:87-90.

Cao, J., P.R. Henry, R. Guo, R.A. Holwerda, J.P. Toth, R.C. Littrell, R.D. Miles and C.B. Ammerman. 2000. Chemical characteristics and relative bioavailability of supplemental organic zinc sources for poultry and ruminants. J. Anim. Sci. 78:2039- 2054.

Hill, D.A., E.R. Peo, Jr., A.J. Lewis and J.D. Crenshaw. 1986. Zinc-amino acid complexes for swine. J. Anim. Sci. 63:121.

Leeson, S. 2003. A new look at trace mineral nutrition of poultry: Can we reduce the environmental burden of poultry manure? In: Nutritional Biotechnology in the Feed and Food Industries: Proceedings of Alltech’s 19th Annual Symposium (T.P. Lyons and K.A. Jacques, eds). Nottingham University Press, UK, pp. 125-129.

National Research Council. 1994. Nutrient Requirements of Poultry. 9th rev. ed. National Academy Press, Washington, DC.

O’Dell, B.L. and J.E. Savage. 1957. Symptoms of zinc deficiency in the chick. Proc. Fed. Soc. 16:394.

Pimentel, J.L., M.E. Cook and J.L. Greger. 1991. Research note: Bioavailability of zinc-methionine for chicks. Poult. Sci. 70:1637.

Robbins, K.R. 1986. A method, SAS program, and example for fitting the broken line to growth data. Univ. Of Tenn. Res. Rep. 86-09. Univ. of Tennessee Agric. Exp. Sta., Knoxville, TN, USA.

Roberson, R. and P.J. Schaible. 1958. The zinc requirement of the chick. Poult. Sci. 37:1321.

Wedekind, K.J. and D.H. Baker. 1989. Zinc bioavailability in feed-grade zinc sources. J. Anim. Sci. 67(Suppl. 2):126.

Wedekind, K.J., A.E. Hortin and D.H. Baker. 1992. Methodology for assessing zinc bioavailability: Efficacy estimates for zinc-methionine, zinc sulfate and zinc oxide. J. Anim. Sci. 70:178-187.


Authors: T. AO and J. PIERCE
Alltech-University of Kentucky Nutrition Research Alliance