Antibiotic growth promoters (AGPs) will be withdrawn from January 1st 2006, what effects will this have and should we be concerned?
Why has this situation come about? The original concerns with AGPs were that they cause resistance in bacteria in animals and these might spread resistance to humans either by the organism itself or via their genetic material and possibly jeopardise the use of some related antibiotics that are vital, last-resort treatments. There is still much debate over this issue and the relative risks of resistance transmission appear to be very small, especially with this last group of AGPs to be withdrawn. Two of which, will remain in use in poultry as anticoccidials.
Should pig producers and their vets be concerned with the removal of the AGPs and what can we expect to happen? Previously, there was a panic when the former growth promoters were withdrawn but after a short while everybody adapted to the new situation. In Denmark in 1998, after the ban on all growth promoters, there was a definite increase in the incidence of diarrhoeas and consequently, in the use of medicinal antibiotics. Certainly in the UK, this concerned the authorities and the Pig Veterinary Society, NPA, MLC, BPEX and RUMA have tried to alert members and farmers to the changes and how to minimise the impact of the ban. Nutritionists have also been hard at work with diet modifications and additions of enzymes and acids to help especially at weaning time. Many producers have also been experimenting with the changes and trying a number of alternatives to growth promoters with sometimes mixed success and often a loss of performance.
Most growth promoters had a stabilising influence on the gut flora and an 'antibacterial effect', especially improving the performance of younger pigs in both growth and FCE. When they were removed a number of diseases increased, such as post-weaning diarrhoea and non-specific diarrhoeas in large growing and finishing pig units, with a consequent loss of performance. AGPs generally worked better in dirtier and more stressful environments where infectious challenge was higher, so this could be expected.
Pig disease tends to occur at certain times and situations. Escherichia coli infections are common and normally associated with post-weaning diarrhoea. It is not usually a major problem as the pig grows older. Spirochaetal diseases, such as 'colitis' caused by Brachyspira pilosicoli, usually develops at the back end of the nursery or grower period. It is commonly mixed with 'ileitis' (Lawsonia intracellularis), which occurs at the same time, and causes a sticky grey diarrhoea and soiling of the pig's behind. The acute haemorrhagic form of ileitis 'bloody gut' usually occurs later in the late finishing stage and can be a significant cause of loss from sudden deaths. Swine dysentery, a much severer infection, and frequently associated with blood in the diarrhoea, can occur usually from late grower through to finisher and can be a persistent problem especially in solid floor systems. The number of submissions of pig diarrhoea cases and their diagnosis to the Veterinary Laboratories Agency in 2003 is presented in Graph 1 and gives a general incidence of occurrence in the UK.
Graph 1. Number of recorded VLA submissions by disease in 2003
(Source: VIDA 2003, 2004)
However, since post-weaning multisystemic wasting syndrome (PMWS) associated with porcine circovirus-type 2 (PCV2) has become widespread, diagnosis has become more complicated. PMWS, where it has become established, is now being seen later, in finishing sheds, usually in the first 6 weeks of entry (11-16 weeks of age). It was always associated with an increase in diarrhoea involving around 50% of the cases, as well as an increase in respiratory disease and as a virus was relatively unresponsive to treatment. In a recent study in Denmark, Jensen and Boye (2005) looked at the occurrence of various infections from tissue samples of the small and large intestine taken from 140 pigs, aged between 8-16 weeks of age, which had had signs of diarrhoea or colitis.
Graph 2. Identification of various diarrhoea causing agents from Danish pigs aged 8-16 weeks
(Source: Jensen and Boye, 2005)
The ileitis organism was identified in 49 pigs, followed by the dysentery organism and the colitis bacterium in 13 cases. Other spirochaetes were also found, mainly B. innocens (11), which is frequently found in the UK, but is thought not to be associated with disease. PCV2 was identified in 25 pigs and the gross visual PCV2 lesions were described as being similar to ileitis. Many of these infections were mixed but interestingly, there was a significant antagonistic relationship observed between PCV2 infections and ileitis and especially swine dysentery, which did not occur together at all.
This highlights and possibly explains some of the complicating effects from PCV2 infections found in the field. These effects were encountered during field trials that have been carried out with Tiamutin and Econor, to try to control the increased diarrhoeas that have occurred following the removal of growth promoters and which will be reported next month.
References: Jensen, T.K. and Boye, M. (2005) "Application of immunohistochemistry and fluorescent in situ hybridization for the detection of the porcine large intestinal agents Lawsonia intracellularis, porcine circovirus type 2, Brachyspira hyodysenteriae, B. pilosicoli, B. innocens B. murdochii and B. intermedia". Proceedings Third International Conference on Colonic Spirochaetal Infections in Animals and Humans, Parma, Italy, pp 64-65
Veterinary Laboratories Agency (2004) VIDA - "Veterinary Investigation Surveillance Report" 2003.
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