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This article was published in 1967
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Animal Health Problems associated with Intensive Pig Production
R. K. RYAN, Ph.D., M.V.Sc., Senior Lecturer in Animal Husbandry, University of Sydney
Intensive systems of pig husbandry imply those systems where many pigs are kept in a small area; there is a dense pig population and we all know that as the population density of any species increases so also do the risks of disease. In intensive production it is not only the density of the animals that may lead to disease but also the fact that the management systems may not be suitable.
If it is desirable to produce pigs under intensive systems we have to accept the fact that we have a dense population: economics would not allow us to have otherwise. But we do have some control over the management systems used and we have to ensure that they allow the pigs to maintain homeostasis as easily as possible, always of course keeping within the economic framework of the existing pig industry.
What may be a suitable management method for one population density may be quite unsuitable for another.
What may be an adequate diet for one management system may not be so for another.
What may be an effective disease control programme for one system may be quite unsuitable for another.
The farmer and the veterinarian have to realise these things.
There are many species of animals where density of population alone affects the well-being and productivity of the individuals. The mechanisms by which animal population size is controlled are being actively studied at the moment in the hope that some light will be thrown on human population problems. It is enough to say that the social organisation of most wild animal species depends primarily on maintaining sufficient food for individuals rather than for the species. A common mechanism is the maintenance of territories by individuals, pairs, or family groups. Those individuals not in possession of territories emigrate or die. In confined and overcrowded populations of animals the maintenance of territories is impossible and most of you will be aware of the Bruce and Lee effects that occur in mice and rats. These are in well-fed populations. If also food is in short supply then anarchy reigns. But this does not necessarily imply we should expect similar problems in intensive pig production. The population is of a different type to that in a wild population. The most crowded segment of the population is immature stock, the males of which are castrated. There is control over breeding stock. There is no shortage of food. The forces of social organisation in natural populations exert their greatest effects at times of breeding activity and food shortage, and apart from competition, are characteristic of adult animals.
If we have control over our breeding pigs, dispose of their progeny before sexual maturity, and there is no food shortage in our population then these phenomena that limit natural populations should be of no importance in intensive pig farming. It is important then to realise that our pig population will consist of two different segments: 1. The breeding herd; and 2. The physiologically immature production units. The management methods for both should differ.
We can't afford to have overcrowding in our breeding herd and we see the trend to individual feeding stalls, sow cubicles, and even a reversion to tethering sows, but this time inside, in individual stalls.
However, this talk will deal mainly with the problems of the immature production herd.
Health problems due to infectious agents will arise: 1. If there is the introduction of a pathogenic organism into a susceptible animal population. The population may be susceptible because of lack of previous experience (contact) with the particular organism or because the normal body defences are impaired; and 2. If the type of housing and management methods encourage the multiplication and spread of organisms already existing in the animal population.
Successful intensive husbandry therefore has to minimise the entry of "foreign" organisms, endeavour to maintain the defence mechanisms of the host, prevent, if possible, a multiplication of undesirable organisms, and impede the spread of organisms from one host to another. I use the words "minimise", "endeavour to", "prevent if possible", etc., on purpose, as I think we have to be practical about this and realise it is perhaps impossible to be absolute in our control measures.
A. Minimise introduction of a potential pathogen into a susceptible population
In intensive units some degree of quarantine is probably advisable. Quarantine restrictions aimed at restrictions on humans are probably overrated in importance. What can you bring on to a farm? If we ignore S.P.F. farms it is pretty hard to muster a good argument for quarantining a piggery against people. Perhaps it is a little easier to justify quarantining against pigs, but of course, not all intensive units are self-contained closed herds many of them buy in pigs for fattening. These piggeries will always have trouble, not so much because disease organisms are introduced on to the farm, but because the stressful situation of shifting pigs allows existing organisms to gain the ascendancy. But if we think of a large closed herd for the moment, quarantine against the entry of outside pigs is of benefit. It is not sufficient to put some newly purchased pigs in an isolation pen for a couple of weeks and if they remain healthy then add them to the herd. A pig could have anything but remain clinically normal. Probably tests for leptospirosis and brucellosis should be carried out, and it must be remembered pregnant sows can bring in swine fever in the foeti. But probably the piggery will have already any of the other organisms the new arrivals may have. I suppose this is rather a sweeping statement. Different serotypes of some organisms have been shown not to be common to all dairy farms but I don't know that this is so in pigs and it is certainly not so when dealing with piggeries that buy in store pigs.
However, if you will accept my statement for the moment that entry of disease organisms into a piggery is not the main worry, then pig health in these units depends primarily on maintaining the defence mechanisms of the host, preventing a multiplication of undesirable organisms, and impeding the spread of organisms from one host to another.
B. Maintaining the defence mechanisms depends on the conditions in the piggery allowing the pig:
1. To maintain homeostasis, i.e. the stability of the cellular environment—the temperature, osmotic pressure and pH of the cellular environment must remain fairly constant; and 2. To maintain normal activity of the reticulo-endothelial system.
Homeostasis. Adequate food and water will be taken for granted but the climatic components of the environment have to be considered. The pig must be able to keep warm and to lose heat. In the Australian environment perhaps we don't have to go to the extremes of housing as is done overseas; perhaps we should be trying to develop housing specifically for our own environment. The pig is fairly flexible in the way it can handle changes in temperature. In cold weather a herd will huddle together and its metabolism will be that of a large single unit, whereas in hot weather the herd will separate and its metabolism will now be that of many individual units. Housing will probably allow huddling and if not, as in sow cubicles etc., then more strict environmental control is necessary (reduce cold winds, provide bedding). Really intensive housing may not allow too much spreading out of individuals so some help will have to be given to allow the pigs to lose heat effectively in very hot weather, remembering that the pig loses heat mainly by evaporation from the body surface if it is allowed to wallow (sweating is negligible) and by heat transfer and evaporation from the respiratory surfaces. The provision of sprays and/or plentiful ventilation is desirable. An increase in humidity decreases the efficiency of heat loss by evaporation, so a micro-environment of high humidity must not be allowed to develop—therefore air movement is important.
Reticulo-endothelial system. I am thinking here mainly of maintaining normal phagocytic activity. This is blocked by:
1. Failure to maintain homeostasis;
2. Adreno-cortico-steroids;
3. Iron injections.
The important thing here is blockage of the reticulo-endothelial system by the adreno-cortico-steroids. Stresses have to be reduced to a minimum. Speaking only of the pig from birth to market, what are the stresses it is likely to encounter?
1. Changes in climatic factors. This depends on housing but remember that the micro-environment is more important than the environment in the whole shed and the pig is able himself to vary the micro-environment. The environment in which the pig actually lives may not vary as much as the casual observer believes.
2. Bullying, weaning, castration, shifting to other pens, changes in food, marketing. It is the management system's responsibility to eliminate or minimise these stresses as much as possible. It is these very stresses that have given rise to an increase in the disease entity known as "oedema disease". It is believed by many that various serotypes of E. coli are responsible for the condition. These serotype populations apparently are present in most pigs but if for any reason they gain the ascendency in the microbial population then one of the many manifestations of oedema disease may occur. The type of symptoms produced depends on the state of sensitivity of the host animal to a specific antigen released from these organisms. There is a tendency now to ascribe almost all the diseases of young pigs to this entity and to explain the variation in symptoms to the prior experience of the host. Whether this is true or not, it emphasises very clearly the importance of management stresses in the production of disease. No intensive unit can afford to ignore these management stresses for these pathogenic serotypes may be rapidly transmitted in a dense population of pigs.
Let us consider how these previously mentioned stresses may be overcome in an intensive unit.
First of all, bullying or perhaps just plain competition. Ideally, the smaller the group the better, but economics come into things here and I think we have to accept the fact that individual litters cannot be kept separate. To minimise this competition we can grade pigs into groups according to size, we can run them together and provide barriers with graded openings to allow the pigs to sort themselves, and we must provide plenty of feeding and watering space. Batch farrowing helps in that a number of sows farrowing together is more likely to result in groups of even size being formed. There is a trend now for birth-to-market pens which eliminate this shifting of little pigs from pen to pen, but unless precautions are taken it leads to pigs of uneven size being grouped together, and wastage of space in pens. These difficulties can all be overcome. Birth-to-market pens will decrease the incidence of oedema disease and allow porkers to be sent to market anything up to a week earlier. To use these pens you don't have specialised farrowing quarters but rather removable farrowing equipment. Economies of space are achieved by first of all the sow being with the litter and then by marketing at two stages—porkers and baconers—so that half the herd is marketed at porker weight and half at baconer weight. Grouping of pigs of equal size is achieved by farrowing sows communally (this means oestrus has to be synchronised) and then allowing the multiple litters to have the run of a single pen but gradually to grade themselves by these barriers with different-sized openings.
Weaning, of course, cannot be avoided but probably pigs should not be weaned before they are eating 1 lb. of creep feed. No matter if you are weaning at five weeks or eight weeks the management of the sow should be such that she hasn't much milk when the young are weaned and a good way is to reduce their water supply. It is better done this way than by gradual reduction of feed as weight loss during lactation results in a reduced yield of milk of higher fat content. Fat is the most variable constituent of sow's milk and the most readily influenced by feeding. The fat percentage, although very erratic, is on average some 8.5 per cent or 45 per cent of the dry matter, but tends to reach a peak around the third week of lactation and has been reported as high as 17.2 per cent. This sudden, very high fat level in the diet, together with the known trough in the immunity of the pig to disease around this time may be of considerable significance in the incidence of piglet scours which frequently occurs at about three weeks of age.
It should be remembered that piglets at about three weeks of age have a minimal level of immunity since they have mostly lost that which was acquired passively from the dam and have not yet had time to establish active immunity. Therefore any stress at all should be avoided during this period.
Castration is a stressful situation. There has been much interest during the last five years in the performance of uncastrated male animals.
In cattle and sheep, arguments can be put forward as to why, in some forms of production, the males should not be castrated. Most work on pigs suggests that castration is desirable but most of this work is based on pigs over four months of age. If the farmer can be sure of getting his pigs away before that age and is selling direct to the slaughter house then serious consideration should be given to eliminating yet another stressful situation. This could well fit in with the idea of efficiently using space in birth-to-market pens.
Changes in food is the other stressful situation mentioned initially. This type of situation is full of danger as it allows, far too readily, changes in type of microbial population in the gut. These changes in food may be difficult to trace during a clinical investigation as the protein content of barley in a single paddock may vary from 6-16 per cent.
I am afraid many of you may think I have been spending too much time on situations that may occur in any type of pig farming not just in intensive units, but I would like to emphasise that stressful situations of a psychological nature are more likely to occur under dense population conditions and it may be as suggested that the adreno-cortico-steroids block the reticulo-endothelial system to such an extent that the defence mechanisms of the host can no longer counteract a change in intestinal flora or fauna.
Preventing multiplication of undesirable organisms is a problem in intensive units. There are several ways to approach this. One is by hygienic measures. The concrete floor is an approach of this sort. It can be hosed frequently and if this is done conscientiously, and the construction of the housing is such that there are not too many nooks and crannies then this method of housing can be successful. Deep litter is another approach but perhaps a little harder to manage and disease breakdowns do certainly occur. Mr. Gordon has told me of serious outbreaks of Trichuris in pigs housed on litter.
Another approach is the all-in all-out system adopted by poultry farmers. This fits in very well with the birth-to-market pen idea I have mentioned and, of course, depends on batch farrowing. This appeals to me as being the best method of breaking the disease cycle in production units. It still leaves the problem, of course, of the breeding segment of the herd, but as these are older they are not as susceptible to disease.
The other consideration was impeding the spread of organisms from one host to another. In an intensive unit this is difficult. Slatted floors have become quite common overseas and are not uncommon here. The idea of these was first to reduce the labour required for cleaning but, provided the density and traffic is correct, they also reduce the transmission of organisms that are spread via the faeces.
Overseas the trend has been to have solid pen divisions extending from ceiling to floor. Most of these units are controlled environment units and the capital invested is quite considerable. These aim to reduce air borne infections of which enzootic pneumonia is a fine example. This can also be achieved by the "sweat-box" type of housing as used in places in Ireland and Great Britain. If, as is suggested, the viral particles adhere to the dust particles in the air and are transmitted by this means, then it is possible that excess ventilation may reduce the incidence of the disease by diluting the density of viral particles. In a climate such as exists in Australia this is a possibility worth considering provided there are suitable micro-climates available to the pig.
So far the discussion has centred mainly around upsets in animal health caused by living organisms and whether they exert a primary or secondary effect. Those mentioned have by no means exhausted the possibilities, and there is no suggestion that they are specific problems associated with intensive units only. But, of course, intensive units are plagued with other worries more specific for this type of production. Tail-biting can become serious. Leg and foot problems, particularly amongst breeding stock, are not uncommon. These occur more frequently on very rough concrete or in pens completely slatted.
And finally, since intensive units usually involve a considerable capital expenditure, the operator is usually more aware of the economics of production and the level of management is quite frequently above average. This may result in faster growing and more efficient pigs and it is now becoming evident that the previously accepted nutritional standards are not necessarily correct and are possibly sub-optimal. The classic example is the Ca requirements of growing pigs and Ca:P ratio. The incidence of atrophic rhinitis has increased wherever the performance of pigs has improved. It has appeared in many S.P.F. farms where the management is far above average. Just recently some very convincing evidence has come forward stating that this condition is just a sign of generalised osteitis fibrosa which occurs only in hyperparathyroidism—due to insufficient body Ca. The 200 lb. pig in 200 days is getting to the stage of the 200 lb. pig in 150 days and the Ca and P intake in rations has not been increased in proportion to the faster growth rate. Whereas previously 0.6-0.8 per cent Ca was considered sufficient the figure is more likely to be around 1.2 per cent today, and it must not be forgotten that as Ca increases in the ration so Zn must increase also. We must today think of rations in these intensive units as containing 1.2 per cent Ca: 1 per cent P with 100 ppm Zn. I think this talk would have been better titled "Some Animal Health Problems Associated with Intensive Pig Production" rather than "Animal Health Problems Associated with Intensive Pig Production", as you know as well as I do that I have only scratched the surface.