By Laia Blavi and Hans Stein, University of Illinois, Urbana-Champaign
The European Union banned the use of antibiotics as growth promoters on Jan. 1, 2006, and since that time, most producers have utilized zinc oxide to mitigate losses in production and reduce nursery pig mortality. In the United States, on Jan. 1 of this year the Food and Drug Administration implemented a new policy that resulted in discontinuation of the use of medically important antibiotics to promote growth, which means that zinc oxide may be more important in the future in managing intestinal health of weaned pigs.
Zinc is an essential micronutrient for all living organisms. The dietary requirements for weanling pigs are 80 milligrams per kilograms (National Research Council, 2012), but pharmacological concentrations of zinc (2,000 to 3,000 milligrams per kilograms) may enhance growth performance and reduce the prevalence of diarrhea (Case and Carlson, 1996; Hu et al., 2012). However, zinc competes with calcium for absorption through channel proteins on the brush border membrane in the pig small intestine (Bertolo et al., 2001), and it is, therefore, possible that elevated levels of dietary zinc interfere with absorption of calcium.
Swine diets are based on plant ingredients and most of them contain phytate, which is an antinutritional factor for humans and animals. Among other things, phytate may chelate nutritionally important cations such as Cu+2, Zn+2, Mg+2, Mn+2, Fe+2, and Ca+2 (Selle et al., 2009). Therefore, phosphorous, calcium and zinc may bind to phytate, which may also affect absorption of calcium and phosphorous. However, during the last decades, microbial phytase has been used in swine diets to increase not only phosphorous absorption (Selle and Ravindran, 2008), but also calcium absorption (González-Vega et al., 2013). However, because of the interactions among, phytate, phosphorous, calcium and zinc, it is possible that the effects of zinc in the diet may also affect the effectiveness of phytase, but no research has been conducted to address this question. Therefore, an experiment was conducted to investigate effects of dietary zinc concentration on the ability of phytase to improve the standardized total tract digestibility (STTD) of calcium and the apparent total tract digestibility (ATTD) of phosphorous in diets fed to pigs.
A total of 56 growing barrows (average BW: approximately 33 pounds) were allotted to seven dietary treatments. A corn-based basal diet was formulated with either zero or 2,400 milligrams per kilogram zinc from ZnO and zero, 1,000 or 3,000 FTU of phytase per kilogram, and a calcium-free diet was used to determine basal endogenous losses of calcium. Experimental diets were fed for 13 days and feces were collected from the feed provided from Day 6 to Day 11.
Results of the experiment indicated that the STTD of calcium increased as the concentration of phytase in the diet increased, but were less if ZnO was used than if no ZnO was added to the diet (Figure 1). The negative effect of ZnO on calcium digestibility was independent of the concentration of phytase in the diet.
The ATTD of phosphorous also increased as the concentration of phytase increased in the diet, but as with calcium, the digestibility of phosphorous was reduced if the dietary concentration of ZnO increased.
Figure 1: Standardized total tract digestibility of calcium in pigs fed diets containing different levels of microbial phytase (zero, 1,000 or 3,000 FTU phytase) without or with ZnO addition.
In conclusion, results of this experiment indicate that pharmacological levels of zinc in diets for pigs may reduce calcium and phosphorous digestibility, but addition of microbial phytase to these diets may partly ameliorate this effect. As a consequence, if pigs need pharmacological levels of zinc, dietary concentrations of calcium and phosphorous in diets for pigs that are around 33 pounds may need to be increased by 4% and 9.5%, respectively, or diets need to be supplemented with microbial phytase to prevent reduced absorption of calcium and phosphorous. Inclusion of microbial phytase increased the STTD of calcium and also the ATTD of phosphorous, confirming that dietary phytate interferes with calcium and phosphorous digestibility.