Increasing zinc via an inorganic source (ZnO) in high calcium finisher diets improves growth performance

Zinc (Zn) is important for protein, carbohydrate and lipid metabolism as it is a component of many enzymes involved in these processes. Because of its role in protein synthesis, Zn is important in the diet of the finisher pig, where fast lean growth is desirable. When formulating pig diets, limestone (CaCO₃) is commonly included as a least cost energy diluent, resulting in increased calcium (Ca) levels. However, increasing Ca above 1.5% inclusion can cause a Zn deficiency (Borah et al. 2014) in grower pigs, resulting in parakeratosis. The current study was designed to determine if increasing Zn level using either an organic or an inorganic source, is effective in offsetting any potential negative effects of including high levels of Ca (1%) in finisher diets.

Sixty Large White x Landrace (PrimeGro Genetics) immunologically castrated males were selected at 14 weeks of age (49.6 kg ± 0.43; mean ± SEM) and housed in individual pens with ad libitum access to feed and water. Pigs were randomly allocated to one of three dietary treatments (n=20) and fed over a period of 35 days. Treatments were: a control finisher diet (13.4 MJ digestible energy (DE)/kg, 0.54 standardised ileal digestible lysine/MJ DE), with 2% limestone (CaCO₃) (1% dietary Ca) and basal Zn at 70 ppm Zn; the control diet with Zn increased to 550 ppm using ZnO (0.06%); and the control diet with Zn increased to 550 ppm of Zn from an organic zinc (Bioplex Zn^® 0.33%). Pigs were weighed at d 0, 21 and 35, with feed intake measured during these periods. Back fat was measured at the P2 site on d 0 and 35. Hot standard carcass weight (HSCW) and P2 were measured after slaughter. Statistical analysis was conducted using ANOVA (IBM SPSS, Version 21.0; USA).

Inclusion of 550 ppm of ZnO improved FCR compared to other treatments from d 21 to 35 and from d 0 to 35 (P < 0.05; Table 1). The ZnO at 550 ppm also improved ADG from d 21 to 35 compared with the other treatments; however ADG was not greater (P > 0.05) than for the control diet over the entire finisher period. The HSCW was heavier (P < 0.05) in pigs fed diets supplemented with ZnO compared with the organic source, but not different (P > 0.05) from that of pigs fed the control diet with 70 ppm Zn inclusion. There was no difference (P > 0.05) in P2 between treatments. The outcomes from this study indicate that increasing concentrations of ZnO in finisher diets with high Ca levels improved growth performance. This response may be due to ZnO offsetting any potential negative effects of Ca in the diets or via the anti-microbial properties of ZnO modifying gastro intestinal tract microbiota (Pieper et al. 2012). Further research is required to verify the mode of action and determine the efficacy of lower ZnO doses. However, it is important to also consider environmental issues and diet costs when formulating feed rations to offset Zn deficiency and (or) improve growth performance.

Table 1.  Influence of feeding a control diet, or diets with 550 ppm inorganic or organic Zn, on performance and carcass measurements. Values are mean ± SEM