Differential effects of zinc oxide and a preparation of organic acids and an essential oil on post-weaning diarrhoea

Weaning of pigs causes a growth check and can render pigs more susceptible to post-weaning diarrhoea (PWD). This condition is associated with proliferation of β-haemolytic strains of enterotoxigenic E. coli (ETEC) in the small intestine. Numerous dietary and management strategies to control/mitigate PWD are used, such as zinc oxide (ZnO), with the use of organic acids and (or) essential oils (EO) also reported to aid in the control of PWD (Vondruskova et al. 2010). This experiment examined the proposition that supplementation of a commercial product containing organic acids, cinnamaldehyde and a permeabilising substance in a diet for pigs infected with ETEC will decrease the incidence of PWD commensurate to ZnO.

A total of 72 entire male pigs (Large White × Landrace) weighing 7.2 ± 1.02 kg (mean ± SD) and weaned at 22.5 d of age were habituated in pens of four and stratified to a completely randomised block design of three diets and live weight (six pens per treatment). Diet treatments were: base diet without antimicrobial compounds (contained 100 mg ZnO/kg of feed in the vitamin/mineral premix) (Control); Control plus 0.3% ZnO; and Control plus 0.15% OACP [OACP; organic acids (formic, propionic, acetic), cinnamaldehyde, and permeabilising substance; Biotronic Top 3^®, Biomin Australia Pty Ltd]. Feed (10.4 MJ net energy/kg, 213 g/kg crude protein, 13.5 g standardised ileal digestible lysine/kg) and water were offered ad libitum for 21 d. Pigs were orally infected with 9 mL aliquots of 1.03 × 10⁹ colony forming units/mL of an ETEC (serotype O149:K98:K88) on d 3, 4 and 5 after weaning. Faecal swabs were taken on d 0, 3, 5, 7, 9 and 11 after weaning for assessment of E. coli shedding. Faecal consistency (FC; ranging from 1–4, with 1 being firm, well-formed faeces and 4 being faeces of watery consistency) was assessed daily for the first 14 d, and a diarrhoea index (DI) was then calculated. Data were analysed by one-way ANOVA using SPSS (v. 21, IBM). For the E. coli score, the effects of time before and after infection with ETEC were tested using repeated-measures ANOVA. Chi-square analysis (IBM SPSS, Version 21.0; USA) was used to compare the percentage of pigs having PWD between the different diets.

The overall infection with ETEC was relatively low, with 14/72 pigs infected having diarrhoea. Approximately 4% of pigs fed ZnO had PWD in the 3 weeks after weaning, which was lower than pigs fed OACP (29%, P = 0.024) or the Control (25%, P = 0.047) diets (Table 1). There was no difference (P = 0.745) in PWD between pigs fed the OACP or Control diets. This corresponded to the DI, which was lower for pigs fed the ZnO diet compared to either the OACP or the Control diet (P = 0.026). The E. coli score increased after infection (P < 0.001), with no difference between treatments (P = 0.987). No interaction between day and treatment was detected (P = 0.442). Zinc oxide may protect epithelial cells from ETEC by inhibition of bacterial adhesion and internalisation thereby improving intestinal barrier function (Roselli et al. 2003), which in the present study may explain the decrease in PWD and DI but not in ETEC shedding.

Table 1.  Effects of dietary treatment on post weaning diarrhoea (PWD), the diarrhoea index (DI) and E. coli scores before (d 0–3) and after (d 5–11) infection with enterotoxigenic E. coli