Feeding sick pigs

Dr Ioannis Mavromichalis
How to properly feed sick pigs is probably the most important question scientists throughout the world will struggle to answer in the next ten to twenty years. As we move closer to a global economy based heavily on industrial pig production, health and diseases become more and more important from an economic point of view.

The problem with sick pigs, even subclinically sick, is that they exhibit anorexia, or simply they don't eat much or at all. So, what causes anorexia and what should we do about it at the farm level?


First, we must understand that anorexia, or loss of appetite, is an integral part of the overall host acute phase response to disease. The animal simply refuses feed and its metabolic burden to inhibit the proliferation of pathogens. This is achieved by the following mechanisms:

1. Reduced feeding activity reserves energy for immune system functions. Of course, this energy comes from body lipid reserves and prolonged dependance on these stores emaciates animals. But, at the begining of a disease, it is actually beneficial!

2. Reduced nutrient availability limits the extent of pathogen proliferation. Pathogens in the gastrointestinal tract have first access to nutrients from feed, especially if digestion is impaired due to the disease, as is often the case with gastrointestinal disorders.

3. The metabolically negative effects of the acute phase response are limited. The acute phase response is the first response immediately after an infection. During this time, the metabolic state of the animal is switched from anabolism and growth in the healthy pig to catabolism and muscle loss in the diseased pig. Excess absorbed nutrients are thus considered 'toxic'!

4. Glucagon production is enhanced and the immune system response is enhanced. Under experimental conditions, force-feeding infected animals increased mortality and reduced survival time, further illustrating the beneficial effects of anorexia. However, experience from human trials indicates that long-term anorexia is equally detrimental because restricted food intake beyond the first 7-10 days of disease outbreak greatly decreases the chances of a rapid recovery.

Intervention strategy

Because reduced feed intake is always associated with reduced growth rate, a common intervention strategy is to increase dietary nutrient density to supply the pig with nutrients that potentially limit growth. However, increasing lysine or protein concentration or treating pigs with porcine somatotrophin, an anabolic agent, failed to increase protein deposition and overall growth rate in pigs experiencing a high level of immune system activity.

In conclusion, we are still far away from understanding how to feed pigs under disease stress. We know that forcing them to eat is not beneficial in the short term, but we also experience productivity losses when anorexia prevails. We also understand that nutrient requirements for fighting disease are quite different from those required for growth. The next challenge is how to provide a diet that actually helps the pig to fight the disease. Up to now, we have been trying to make it just keep growing!


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    John Gadd

    Interesting thouhghts on an important subject!
    About 10 years ago American researchers put forward the idea of `Challenge Feeding` as a(partial?)guideline solution to altering the diet of growing pigs so as to counter the effect of disease on the pig`s need to bolster its immune defences when disease does threaten/appear. The idea has never caught on despite seeming to be a natural development for the feed manufacturers to follow up.
    I have a few ideas as to the reasons why it may have receded into obscurity (an important one of which is now solved) but would Dr Mavromichalis, as an up-to-date professoional pig nutritionist, like to comment on the concept?
    I have a gut feeling that the idea is too promising to be left to rest.

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    Dr Nikolaos Kotrotsios

    I'm still wondering about its occurrence, magnitude and duration to get a useful approach to this considerable confused phenomenon. We should focus to the sources of variation in anorexia from the animal itself, the pathogen type, the environment it is kept in and on the food composition. Probably, I agree with you, to have a correct answer in the next ten to twenty years.


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    Dr Ioannis Mavromichalis

    Dear John, first allow me to remind our readers what Challenge Feeding is all about. It involves designing a farm-specific nutrition program by giving or challenging a selected group of pigs with an unlimited diet a couple times a year. The accumulated data, which include growth performance and carcass characteristics, are used to create a lean growth curve that is used to create a nutrition program that matches the genetics, facilities, management, and health status of the pigs. The end result is maximal performance and yield at minimal cost, which leads to maximal profitability. There are many reasons why this specialized but very effective type of nutritional intervention strategy is not used today, at least as much as it should have been. The main reason, in my opinion and experience, is the lack of trained professionals, who must be employed to do this tedious job. Nutritionists are focusing mostly on additives and in traditional nutrition approaches, like the one we are discussing here. And, feed companies and other nutrition suppliers are considering this and any other free technical service as an extra expense that is becoming a burden, especially as they must turn over a higher and higher profit each year! The only solution is for pig producers, at least those large enough to afford it, is to hire their own technical stuff, train them to handle this program in-house, and only use external help to update things. It will be more expensive than depending on your nutritional supplier to provide it for free on an ad hoc basis, but the returns are substantial and real!

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