Post Weaning Scours and Zinc Oxide
NADIS is a network of 40 veterinary practices and six veterinary colleges monitoring diseases in cattle sheep and pigs in the UK. NADIS data can highlight potential livestock disease and parasite incidence before they peak, providing a valuable early warning for the month ahead. |
July 2004
By Mark White BVSc DPM MRCVS
NADIS Pig Disease Focus
Post Weaning Scours and Zinc Oxide
Under modern production systems, scouring after weaning of pigs at less than 4 weeks of age is commonplace and, over the years, strategies have been developed to prevent disease or offset the effects.
One of the most common techniques is to incorporate Zinc Oxide in the diets for the weaned pig for 2 weeks.
However, the use of Zinc Oxide is now under threat and it is expected that, on environmental grounds, the use of high levels of Zinc Oxide in diets will be banned by the EU by next year.
It is pertinent to look back over the biology of post weaning scours and the history and effect of Zinc Oxide as a way of spotting alternative arrangements in the future.
Gut Development
From birth, the piglet’s digestive system is geared towards processing milk-based fat, protein and carbohydrate.
These are relatively simple molecules that the primitive gut can cope with. As the piglet grows, colonisation of the gut occurs with a wide range of microbes, most of which will originate from the sow.
In the healthy piglet, there is a stable balance between helpful and harmful organisms in an environment that is influenced by the fact that the piglet eats a liquid diet of simple composition (milk) little and often.
When weaned, under conventional “crash” weaning systems, massive changes occur to the gut of the pig.
The diet changes from liquid “on tap” to solid based, containing fat, protein and carbohydrate that will be vegetable based.
Cooking of cereals and other processing will assist the digestibility and the inclusion of whey proteins and other milk products will offset the changes that the pig meets. The patterns of feeding may also change in that engorgement is more likely to occur “over-loading” the gut.
The stomach is acidic normally and acts not only to kill off potential harmful microbes entering with the food but to control the pH of the intestine, thus limiting microbial over-growth.
There is a tendency for this effect to be lost or reduced post weaning, potentially allowing a gut environment more favourable to microbial growth.
Furthermore, the lining of the intestine consists of villi – microscopic finger like projections which vastly increase the surface area, allowing improved digestion and absorption of nutrients.
In response to the stress of weaning and as a result of meeting foreign proteins, these villi shrink, reducing surface area and, hence, digestive and absorptive capacity. This will allow undigested food to pass further down the gut where microbial proliferation will occur causing scour.
Treatment
The traditional approach to treatment of post weaning scour has been to use antibiotics in feed or water with variable success. However, in the late 1980’s, the UK industry saw a huge escalation in post weaning scour that, in many cases, was uncontrollable with antibiotics.
Speculation at that time suggested that the upsurge in scours was associated with some strategic changes in diet formulation – particularly the reduction in the use of skim milk powder and its replacement with whey blends etc.
As a result of the problem, high levels of Zinc Oxide were included in the diet following reports from Denmark of high success rates.
2500ppm or more of Zinc included in rations to cover the first 2 weeks post weaning – the period when the gut was developing to cope with the diet changes and the stresses of weaning – proved a saviour at that time.
Other than a brief period of regulatory nonsense that prevented it’s use (because it was being used for medicinal purposes it had to have a medicine licence!) Zinc Oxide has been included in piglet creep/weaning diets fed to more than 80% of pigs ever since and inevitably we have come to rely on its use.
It has never been clear how it works. Zinc Oxide is known to have an antibacterial effect (it has been used for many years in topical antiseptic creams).
What is important is that Zinc Oxide is insoluble and, thus, is gut restricted, passing out in the faeces in an unchanged form. Use of soluble Zinc salts (sulphate, carbonate) at these high levels poisons and kills pigs.
There has been mixed views as to the effect of Zinc Oxide on appetite with producers claiming it limits appetite (which in itself would help reduce scouring), others that is improves feed intake whilst many see no effect on appetite at all.
Assuming that high levels of Zinc are banned in the near future, producers will rapidly have to find a way of dealing with the weaned pig to offset the risk of scour.
Future Strategies
We may well have to return to the days when milk levels in diets were much higher – with its attendant cost implications. High quality diets will be essential.
The problems may well be offset by weaning a slightly older pig, which not only will suffer less gut change at weaning but will allow longer creep feeding pre-weaning.
It has been known since the 1970’s, that small amounts of vegetable protein in diets before weaning sensitises the gut such that an allergic type reaction occurs when large quantities are met at weaning, promoting scour.
By ensuring that piglets eat at least 600g of creep prior to weaning, this effect can be offset.
Organic acids have been included in piglet rations since the 1970’s in an attempt to maintain low gut pH post weaning.
Recent developments have stimulated interest in these products which have been improved and refined and they may well prove highly valuable in the future.
Similarly, enzymes are widely used in diets to improve digestibility, although problems remain with heat stability in pelleting.
On farm, the art of piglet feeding will have to be re-learnt. In the modern farm, time is at a premium and simply presenting piglets with ad lib creep pellets is easy.
Little and often feeding, possibly in the form of porridge, for the first 7-10 days after weaning may have to become the norm if we are not to see a serious escalation in post weaning scours.
As the range of antimicrobials available has dwindled, we may not be able to rely on their use.
While every effort is made to ensure that the content of this forecast is accurate at the time of publication, NADIS cannot accept responsibility for errors or omissions. All information is general and will need to be adapted in the light of individual farm circumstances in consultation with your veterinary surgeon
Copyright © NADIS 2002
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