non-antibiotic medication can be added to drinking water. Results, as described below, give reason for optimism. It is clear that it is related to the way the gram-negative bac- teria B. hyodysenteriae normally colonises the intestine. Proteins on the bacteria’s outer membrane would normal- ly release “haemolysin toxins” into the villi of gut epithelia.
That would lead to villi degradation and subsequent bleeding, which is characteristic of swine dysentery. In vivo studies demonstrated, however, that when applying the zinc chelate, B. hyodysenteriae was no longer attached to the intestinal cell wall and had been flushed out. The research team concluded that the zinc chelate must therefore be blocking the proper functioning of these outer membrane proteins (OMP). Hence, the zinc chelate is introduced as “OMP blocker.”
Effects on swine farms
In the Netherlands, a team of researchers with GD Ani- mal Health and Intracare carried out a trial to test the
effects of that approach on clinical appearance, faecal quality and excretion of the bacteria. In 2017, the team investigated the situation on two com- mercial pig farms in the Netherlands experi- encing clinical swine dysentery in grow- finisher pigs. • Farm A was a multiplier farm consisting of 670 sows;
• Farm B was a grow-finish farm consisting of
2,180 grow-finish pigs. The research team chose in total 64 pigs in eight pens per farm for close, individual follow-up. As six pigs did not ex- crete B. hyodysenteriae at the start of the trial, the scientists used 58 study pigs to assess the efficacy of the medication in the treatment of clinical signs. Of the 58 enrolled pigs,
30 received placebo (four pens per farm) and 28 received zinc chelate treatment (four pens per farm).
Faecal quality scores At the start of the trial, the faecal quality scores of the individ- ually monitored pigs were quite comparable between all pigs. Yet that was soon to change. The researchers wrote, “The results of this study clearly demonstrated that low concentra- tions of the zinc chelate significantly reduced clinical signs and shedding of B. hyodysenteriae.” Treatment with the OMP blocker, they added, resulted in a significant improvement in faecal quality (see Figure 1), and after six days it was not pos- sible to detect any B. hyodysenteriae in faeces by PCR. They went on to describe that in the placebo-treated group, 17% eventually collapsed and 48% of the remaining pigs re- quired additional therapeutic treatment. The scientists also observed no relapse by clinical appearance and faecal quality on day 14 of the trial.
Within six days All in all, the researchers concluded, treatment with the zinc chelate had ceased the shedding of B. hyodysenteriae within six days and ceases the clinical signs of B. hyodysenteriae in naturally infected pigs for at least an additional eight days af- ter cessation of oral therapy. That resulted in a higher growth rate of treated pigs and improved general health. In addition, the team did not observe mortality and no additional treat- ment was needed. So, while the toolbox is getting emptier with antibiotics and zinc oxide gradually disappearing, the good news is that when one door closes, another one opens.
The research discussed in this article was published in the peer-reviewed journal Veterinary Record in 2019. References available on request.
▶ PIG PROGRESS | Volume 37, No. 2, 2021 17
Not photo- shopped: The difference be- tween using a zinc chelate (left) vs. control.
PHOTO: INTRACARE
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