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Responsible use of antibiotics – resolving a salmonella diarrhoea outbreak without mass antibiotic medication
IN any disease outbreak it’s tempting to reach for the mass medication button to stop the out- break in its tracks and prevent further spread.
In this case study sent in by an experienced veteri- nary colleague, resolution of salmonella infection followed a laboratory- supported diagnosis, all- in all-out pig flow, thor- ough hygiene measures and individual treatments of sick animals.
By necessity it includes staff training in disease control principles.
The veterinarian was faced with a sudden out- break of diarrhoea and
ill-thrift at five to eight weeks of age, affecting 30 percent of weaners.
The pigs were kept in straw-based sheds.
They had been moved there with a trailer.
Sheds had not been properly cleaned nor disinfected between batches.
Neither had the trailer.
Consistent with good veterinary practice, the vet autopsied some af- fected pigs.
Lesions were typical of disease caused by salmo- nella infection or swine dysentery.
Lab results confirmed salmonella typhimurium,
a common type of sal- monella.
Non-recoverable sick pigs were euthanised.
Pigs with recovery pros- pects were isolated and based on the lab antibi- otic sensitivity results, treated with trimetho- prim sulphonamide injec- tions daily.
Survival rates were high.
The farm commenced an aggressive hygiene program.
The pig trailer was pressure washed and disinfected before every week’s pig movements.
Sheds were more thor- oughly pressure washed and disinfected between each batch.
Rodent control was
stepped up because rats carry salmonella and were a risk to the herd.
The salmonella outbreak was resolved within three weeks without recourse to in-feed medication with antibiotics or blanket in- jections of antibiotics.
Ongoing control can be challenging.
It is achieved through rigid adherence to all-in all-out pig flow in each shed, together with thor- ough cleaning and disin- fection between batches.
Feed and water acids can help.
For full effect this re- quires the diligent atten- tion of staff and rein- forcement of health prin- ciples in staff training. Ross Cutler
Take-home message
for removing in-feed
antimicrobial medication:
all-in all-out pig flows rule
IN a controlled study on a large farm, Sun- Pork Farms veterinar- ian Dr Yvette Pollock found all-in all-out pig flow has a bigger impact than “anything else” on herd mortal- ity rates.
Dr Pollock reported her findings at the Aus- tralian Pig Vets AGM in Cairns in July this year.
She compared batch by batch post-weaning mortality performance on a site that was pulse medicated in feed throughout post-wean- ing period with a site (part of the same sys- tem) where a change in pig flow occurred and they were medicated only in water for short periods (and not past eight weeks old).
Like all other per- formance indicators in animal production, there were good weeks and bad weeks.
These occurred whether the pigs were medicated in-feed or not.
On the site, after the pig flow was changed to all-in all-out, and after the medications were removed from the feed, mortality rates decreased for about six months and then rose.
The pig flow change involved once a week weaning (versus twice weekly), fixed numbers into weaner room (and excess going to the other site) and inclu- sion of extra feeders and drinkers.
However, on the site where the feed medica- tion was not changed, though there was no change overall in mor- tality, bad batches (with high mortality percent- age) still happened.
On the site where feed medication was removed, only about 0.5 percent of the in- crease in mortality is likely to be attributed
to feed medication re- moval.
On-farm investiga- tion of mortality and shifting of the water medication dose pro- gram is under way to address this.
In the weaners, mor- tality rates were at their lowest when the feed was unmedicated but, as time went on, there was substantial varia- tion on a week-by-week basis just as there was for the in-feed medi- cated pigs.
Data monitoring shows the effect of re- moving the Selko wa- ter acidification (not so good) and the effect of installing heaters (good) for the three to eight-week-old weaners in winter.
They also show the week-to-week variation in the pigs medicated in feed.
Dr Pollock said: “Too often we think the changes to medication on-farm might be a re- sponse to medication.”
However, as the da- ta in her presentation showed, there was a lot happening.
Animal production systems are dynamic.
They change all the time and must be man- aged and monitored (preferably in real time).
There is much at stake.
Every 1 percent change in mortality rate costs a herd about $3 per pig, per week in inventory.
Every 10g per day reduction in average daily gain costs $3.50 for every pig produced.
Given that there is much more to disease control than medica- tion, it pays to monitor health in the same way other performance is monitored.
Water supply and quality, water addi-
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Australian Pork Newspaper, October 2019 – Page 9
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