Zinc oxide presentation can influence weaner performance

Weaning is associated with a period of feed interruption and a transition to solid feed that can result in transient changes in gut morphology leading to impaired performance. Zinc oxide (ZnO) has been found to benefit gut health with reported effects such as increased expression of antimicrobial peptides, gut flora stabilisation and bactericidal function (Pluske et al. 2007). Zinc oxide is included in weaner diets at rates well above nutrient requirements. Environmental concerns due to low bioavailability and retention of Zn (Case and Carlson 2002) and implication in the development of antimicrobial resistance in enteric bacteria (Yazdankhah et al. 2014) have led calls to restrict the use of ZnO. This study investigated weaner performance when using modified organic versions of ZnO, with the null hypothesis that there would be no effect on performance between ZnO treatments.

Five hundred and sixty male pigs (20 days, 5.86 ± 0.17 kg) entered the experiment over a 4-week period and were sorted by size and assigned to pens (n = 14). Pens were weighed and allocated to one of four treatments using a randomised block design, resulting in 10 replicates per treatment. Treatments consisted of isoenergetic and isonitrogenous weaner diets (14.85 MJ DE/kg, 0.87 g standardised ileal digestible lysine/MJ DE) including no ZnO (control), 3000 ppm ZnO, 1000 ppm of a protected ZnO (PZnO) or 300 ppm of an enhanced surface ZnO (EZnO). Diets and water were offered ad libitum throughout the 28 days of the experimental period. Pens of pigs and feed refusal were weighed weekly and water usage was also measured weekly. Data were analysed by ANOVA with treatment as a fixed factor, entry week as blocking factor and entry weight as a covariate. Removals were tested for significance via Chi-squared analysis. Significant differences between treatments were determined by l.s.d. (P < 0.05, Genstat 18, VSN International, Hemel Hempstead, UK).

There was no significant difference between diets containing no ZnO (control), 3000 ppm of ZnO or 1000 ppm of the PZnO; however, the 300 ppm EZnO treatment pigs consumed less feed, grew slower and ended the experiment significantly lighter than all other treatments (P < 0.05; Table 1). There was no significant difference in morbidity and mortality between treatments (χ²(3) = 5.76, P = 0.124). The lower feed intake of the EZnO treatment suggests that this product may have affected the palatability of the diet, which is supported by a consistent, but not significant, increase in water usage compared to the other treatments.

Table 1.  Performance of weaner pigs fed diets containing no zinc oxide (–ve Control), 3000 ppm of zinc oxide (ZnO), 1000 ppm of a protected zinc oxide (Pro ZnO) or 300 ppm of an enhanced surface zinc oxide (ES ZnO)

The similar performance of the pigs fed PZnO compared to those fed ZnO confirms our null hypothesis and affords us a viable alternative if restrictions on the inclusion rate of ZnO are imposed in the future.