After PMWS- Feeding the High Health Status Farm

Introduction

Through the late 1990's and on into the present century the global swine industry experienced very profound changes. The price crash in 1997/98 was especially traumatic and the outbreaks of CSF and FMD were also particularly damaging. A new emerging disease that became known as Post-weaning Multi-systemic Wasting Syndrome (PMWS) and its related Post-weaning Dermatitis Nephropathy Syndrome (PDNS) then appeared all over the global swine industry and caused havoc on the whole industry supply chain. For production farm businesses this meant very high mortalities after weaning and through the grower phase but also we learnt that reproduction and general health status of the breeding herd was also affected. The disease syndrome we now know is caused by Porcine Cicovirus-2 a variant of the existing PCV virus. There is also known to be involvement with other viral organisms such as PRRS virus. All of this depresses immunity and suppresses growth and feed intake in growing pigs.

We have all learnt that we can beat this disease syndrome by ensuring the best husbandry and hygiene practices and applying what came to be known as the Madec Principles, a 20 point husbandry plan to counter the worst effects of the disease. We also now have very effective PCV-2 vaccines available that are used to good effect all around the world on production farms. One of the hard lessons we have learnt is the sheer importance of on-farm health status and the need for effective biosecurity measures both at the individual business level but also at the industry level. BPEX in the UK accordingly launched a Health & Welfare Strategy to focus attention on health care and health status and to coerce more producers to progress towards better animal health.

Many producers also realise and understand the benefits that accrue from attaining a higher level of health status within their herds and are prepared to invest in programmes of systematic de-population and re-population over a 5-8 year cycle to sustain a high level of health. This brings very significant improvements in the performance of growing pigs but also the sow herds.

The alternative to high health status is operating a sow / grower / finisher unit with an ever decreasing health status propped up with ever increasing antibiotic and other drug inputs to maintain production and upward spiralling costs. Estimates vary but following a full or partial depopulation programme, but herd performance in terms of feed intake, growth rates and FCR's can increase by around 30%. The investment therefore pays for itself quickly and the veterinary profession have been strongly suggesting these programmes for some time.

By applying good biosecurity measures following a de-population or hyper-vaccination programme there is every reason why the improvements should not be maintained for between 3 and 5 years and by year 8 the whole exercise can be profitably repeated.

For the veterinarians involved, this brings a closer involvement with producers over time. For the nutritionists involved, there are new challenges. The provision of nutrient requirements from weaning to slaughter for a given genotype may on a totally new schedule.

High health status pigs (HHSP) have significantly enhanced feed intake characteristics and the indications are that they will respond positively to higher levels of essential amino acids and other nutrients. The danger is that using the same feeding programmes as for a low health status pig (LHSP) may lead to ‘under-achieving pigs' that grow below their potential and that are also too fat to meet market requirments.

The purpose of this paper is to identify those aspects of nutrition where we believe there are robust associations with health status and to provide some pointers where practical nutrition programmes might be influenced.


Defining Health Status

One of the problems in ultimately designing nutrition programmes for specific levels of health status is that it is not easy to define, evaluate and measure herd health status. We can look at the prevailing growth performance in the growing/finishing herd and this will provide a good insight when compared to existing industry benchmarks. The difficulty here is that herds vary significantly in genetics and management and this confounds the assessment. We can go on to collate all available data on lung scores from the abattoirs to provide an overview of the sub-clinical or chronic disease loading carried by the herd. This can also be useful information to build up the picture but again on its own does not give an accurate index of herd health status. The level of pharmaceutical inputs into a particular herd also adds to the story.

Attempts have been made to use specific analytical tools to yield a health status index and the measurement of acute phase proteins is one of these methods. The idea is that when a group of animals experiences a chronic exposure to pathogens without necessarily having overt disease, they will also have highly activated immune systems and the production of an array of cytokines and other cellular material such as expanded lymphocyte lines will be evident. Acute phase protein production is also an integral component of these responses and could provide a tonic response. This means that the level of acute phase proteins is not a rapid and immediately responsive effect but the levels will be determined by the animals recent immunological / pathogenic history over previous weeks. Amory et al (2002) have explored this possibility but only saw modest correlation coefficients between acute phase protein measurements, lung scores and growth performance in a study including some 35 herds in the West Midlands. This has been developed further more recently.

There is obviously an urgent need for further research in this area but the answer probably will be the use of an index along similar lines to a genetic selection index. We can use all of the information we have available statistically weighted for its importance and its economic value to compute an overall index score for a particular herd within a given industry.

The equation at the end of the day may look something like this:

Health Score Index = !
(ADG*k1 + LS*k2 + PhU*k3 + VE*k4)
where:

ADG = average herd daily gain over the previous 3 months
PhU = pharmaceutical use over the previous 3 months
VE = veterinary consultant subjective evaluation over the previous 3 months
K1, k2, k3 - weighting factors

If this could be simplified to an index scale from 0 (poor) to 10 (excellent) then nutritionists would have a number to base their own nutritional designs upon.

Growth Potential in Pigs

There have been significant and progressive changes in growth parameters in modern hybrid pigs and in terms of average daily liveweight gains to slaughter weight and feed conversion efficiency, great strides have been made over the last 40 years and this process continues. This has emanated from the efforts of the hybrid breeding companies but also our technology in environmental control and also in nutrition have played a role. The real genetic potential is probably in the order of between 120 and 130 days to slaughter at 100 kg when all the technologies are working in concert. This of course in commercial practice is hardly ever realised.


Figure 1
Changing Finishing Weights (kg) in the UK 1970 to 2003
(MLC Yearbooks)

 

Figures 1 through 4 give data from the UK Meat & Livestock Commission's (BPEX) work (Wiseman, J., Varley, M.A. and Knowles, A., 2004) showing the phenotypic changes we have seen in growth and carcase performance in recent changes. Clearly we are dealing with a profoundly changed pig today than we were back in 1970. This implications of these changes on nutritional requirements and management practices are of paramount importance to understand and not only are we dealing with a different genotype, we also have a highly changeable situaiton when it comes to health status

Growth Potential & Health Status

It is a self-evident truth that good growth is linked directly to good health status. Any producer who has carried out a depopulation-repopulation programme and begins a new production cycle with refreshed buildings and high health status pigs will have observed the very rapid growth rates that are achieved in the growing and finishing phases. This also brings a totally new cost structure to the business because of the increased throughput through the available building system but also because of significantly reduced feed costs. Experience suggests that this will continue for a considerable time after the de-population procedure has been carried out and depending on the farm protocols in place of hygiene and general management, this will give an advantage for between 5 and 8 years.

Figure 5
The relationship between growth performance and disease burden (Australian Pig Health Scheme 2003)



The data presented in figure 5 illustrate from the Australia Pig Health Scheme (2003) how an increased respiratory disease burden is related to growth performance to slaughter. With multiple diseases evident on a particular farm, then growth rates will be depressed. This has also been the experience in the UK.

Practical Nutrition For High Health Status Herds

In commercial practice as herds hopefully move towards a higher level of health status, however we define this, we will require a change of strategy. High health status pigs, will have a higher level of voluntary feed intake and one of the consequences of this, even despite improved lean tissue genetics, is that pigs may get too fat at the selected slaughter weight. What may be acceptable and correct calorie/lysine ratios for a ‘normal' pig will not be suitable for a HHSP.

Energy requirements themselves also may need to be totally reviewed to accommodate changing feed intake patterns. Moreover, we know that a profoundly challenged pig will mount a series of immune responses to counter this challenge and this in itself (Koutsos and Klasing, 2001) will divert up to 6% of available net energy to generate the necessary immune functions. The corollary of this is that a HHSP is not carrying this added burden to the energy budget and may need less energy to achieve the same lean tissue growth as FCR improves significantly.

We might expect that the ratios of digestible amino acids required will be very similar at varying levels of health status but the work from Iowa State University (Williams, Stahly and Zimmerman, 1997) has shown that at different levels of immune stimulation (health status) growing pigs will respond differently to amino acid inputs and for higher health status pigs, they may reach their optimum growth at higher levels of amino acid inputs.

A further aspect of nutrition that is important in terms of health status is mineral and vitamin nutrition. If growing pigs have a ‘daily requirement' for some of these macro and micro nutrients, then if higher levels of feed intake are reached, then we may need to alter (reduce) the concentrations of these in both the premix formulation and the final finished feed formulation.


Conclusions

There is obviously a need for much more research in this area and our knowledge is far from complete. We can speculate on changing requirements and animal responses from our available data sets and knowledge but at this point in time we cannot re-formulate a finished feed with precision as health status changes. A priority in this and a basic first step is to establish a working index of health status in order to grade individual herds. This will not only benefit the producer for use in management protocols but also the veterinarian when identifying appropriate actions. This will also make the nutritionists life easier in that a greater level of precision in on-farm formulation will be achieved.

We also require effective working health status-nutrition simulation models that can utilise health index information and facilitate adjustments in formulation parameters. For the moment we can make qualitative changes to feeding programmes on the basis of our current understanding. What is also clear is that once a higher level of health status is achieved, there are very significant cost savings to be had from the accrued growth and feed efficiency improvements.

References

Amory 2001. The effects of the environment on health status and welfare of growing pigs. PhD thesis. Harper Adams University College.

Koutsos, E.A. and Kirk C. Klasing, K.C.,2001. Interactions between the immune system, nutrition, and productivity of animals. Recent Advances in Animal Nutrition. 2001. Pages 173-190. ed. P.C. Garnsworth and J Wiseman. Nottingham University Press.

Wiseman, J., Varley, M.A. and Knowles, A., 2004. Livestock yields now, and to come: Case Study Pigs. In Proceedings of Livestock yields now and to come DEFRA, University of Nottingham, June 2004.

Williams, N.H. Stahly, T.S. and Zimmerman,D.R. 1997. Effect of chronic immune system activation on the rate, efficiency and composition of growth and lysine needs of pigs fed from 6 to 27 kg. J. Anim. Sci. 75: 2463 - 2471.