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We have talked about the inherent variability present in all biological production processes.  This variability is a crucial part of the mechanism of change built into living organisms as it facilitates beneficial adaptation over time.  In commercial agriculture however, variation in growth rates of animals in a group can cause significant negative consequences to profitability. 

Adding to the level of natural variation in production environments is common and in many cases unavoidable due to several factors inherent in the characteristics of the current, dominant technologies in place to produce pork.  But if we were to list the contributors to weight and quality variation from most damaging to least damaging with respect to profitability there would be one clear winner.  Head and shoulders above all other causes is disease.

Disease: the single greatest destroyer of profitability in pig production. 

Disease impact is multi-dimensional and affects all of the big four production drivers of profit.  These include average daily gain, feed conversion efficiency, meat quality characteristics and death loss.  We will be revisiting each of these key determinants of profit in future articles to understand how they are affected by disease processes.  Preventing disease where possible, typically yields much higher profits than treating outbreaks after they occur.  A major reason for this is the variable length of the delays in the sequence of events from outbreak discovery to disease resolution which occur among workers and across farms.


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The signs of emerging disease can take on many forms from dramatic to very subtle in terms of their “visibility” to those working with and observing the pigs every day.  To understand this, it is important to change our mindset to one of precision rather than group average thinking.  The first step in doing that is to begin to see the world as a set of distributions with different probabilities attached to each outcome in the distribution.  Nearly everything you describe as a single value in your daily life from your weight to your age to your checkbook balance is actually experienced as a distribution which you simplify to a single value, like the average or mean or value over a given period of time.

Let’s assume it is the morning and you have just weighed yourself so you have a fresh observation.  For most people, this is their weight in their mind until they weigh themselves again, either tomorrow or next week.  We know in fact, that a healthy individual in a steady-state weight pattern (neither gaining or losing on average over time) will have many weights throughout the course of a single day.  Research has demonstrated that if you weigh yourself every waking hour on the hour each day, you can expect to observe changes in body weight that average from 1-2kg in a single day. 


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Identification process of disease outbreaks

The first event in the sequence is the emergence of symptoms at a level which triggers notice by farm workers.  A little bit of coughing by the pigs when they get up may be considered normal or due to typical ambient dust conditions or air quality in the barn.  What constitutes the change from “a little bit” to an abnormal level is a judgment call reserved to the observer.

Even if a protocol of reporting symptoms is standardized, workers have varying ability to sense the early and often subtle emergence of economically and welfare significant diseases.  They can be tired, busy, otherwise distracted or simply forgetful.  So even when noticed and considered, there will be variation in how severe the symptoms are judged to be and whether they have reached a reporting threshold. 

Once a worker believes the symptoms have reached a reporting level, there is an inevitable lag associated with the ability to respond which can be caused by many things.  For instance, the potential necessity of an on-site veterinary consultation first, the determination of which treatment to deploy and in the case of some pharmaceuticals, researching legal requirements assuring compliance with regulatory restrictions, prescribed withdrawal periods before sales of animals and other limitations should they exist.

After a decision to treat is made and the treatment of choice selected, there are variances in the timeliness of transporting the medication to the site and administering it.  Adding to this variable, sequential process already described is the variance in time required, dependent on mode of delivery to the animal (by feed, water, injection etc.) to reach threshold levels of efficacy in all the affected animals.  After all of this has occurred, some of the animals may die anyway and others may never fully be restored to previous growth and efficiency trajectories which were possible before they became sick. 

It is very likely that subpopulations of animals develop when diseases emerge to symptomatic levels.  Subpopulations form around animals that are similarly, differentially affected by the causative organisms. These subpopulations within the barn form their own distributions of feed intake, growth, deathloss and efficiency of growth.  In group or batch systems, these subpopulations are often not visible to the farm workers and therefore they are not differentially treated leading to increased sub optimization and profit loss.  Lastly, many animals which were completely unaffected may be treated with full therapeutic doses which is costly, inefficient and may cause other problems.

A further consequence of all of this is that the perceived “average” pig in the barn will be used to calculate the economics of treatment.  We will be able to show in future articles how failing to recognize the distributions and subpopulations within the barn almost always leads to an underestimate of the cost of disease and the benefit of vaccination or treatment.  Preventing the profit damaging effects of disease forms the foundation on which precision technologies and more accurate calculations can be undertaken.  Prevention is simpler, more effective and more profitable than treatment.


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