Mareks Disease: Important lessons learnt

Rearers now consider double vaccination of day-old chicks a must
Rearers now consider double vaccination of day-old chicks a must

Last month’s ’Ranger Magazine (www.theranger.co.uk)’ took up the contentious issue of Marek’s disease. One of the reasons why the effects can be so shocking for producers is that whilst the virus is latent there are no obvious signs of disease. An infection in a flock may escape detection until suddenly, without warning, mortality commences. Since by that time there is no cure, prevention is doubly important. For the purposes of this follow-up article, we spoke to two sectors of the industry that play a very important role in minimising the risk of the disease being present in the first place: the pullet rearers whom producers rely on to supply them with problem-free pullets, and the animal health companies who produce the vaccines used throughout the industry.

IMPORTANT LESSONS LEARNT

During the last few years, Marek’s disease has impacted badly on the Free Range sector, and lessons have been learnt the hard way. Many pullet rearers were unfortunate enough to experience Marek’s, and responded by looking very carefully at every aspect of what they do; as a result, the pullet rearing industry today is probably operating to higher standards than at any time in the past.

Having spoken to a number of rearers, it seems that, broadly speaking, the lessons that the sector has taken away from the experience can be summarised as follows:

• There is a very strong case to be made for operating a rearing farm as all in, all out; i.e. no chicks and pullets at same time.

• Double vaccination by the hatchery is strongly advisable. Double vaccination means, quite simply, that day-olds at the hatchery are given a first vaccination in the normal way, and a couple of hours later they are all vaccinated again.

• The storage of the vaccine and how it is administered is highly important. Hatchery audits should be carried out, to monitor and observe; like any process done by humans, there is the potential for error and variability between personnel.

• A healthy chick is imperative if it is to respond to the Marek’s vaccine optimally. Day-old health issues, such as Pseudomonads, can cause high mortality. If treated, the mortality is short lived but in the meantime the chick’s immune system has been suppressed, so that uptake of the vaccine is potentially compromised.

• Likewise, it is important that immunosuppressive diseases like IBD or Chicken Anaemia are kept under control to avoid immunosuppression that may interfere with Marek’s vaccination.

• If there is a level of Marek’s challenge on a rearing farm, this does not mean that all chicks will go on to develop Marek’s in lay. Cases have been recorded where flocks of birds of the same breed have been sent out of the SAME house, and one flock then experienced issues and another did not. This is strong evidence of a link to stressors in the laying environment triggering the underlying disease. There have been cases, too, where some breeds go on to have issues and others do not, and this can often be traced back to day-old chick quality/rearing issues.

• Once an all in, all out status has been achieved, thorough cleaning is essential to reduce the Marek’s challenge. An effective method is for the house to be washed with detergent and disinfectant twice, followed by an ammonia product such as Bio-Oocyst, then gassed with formulin and subsequently locked up for 48 hours. It is important to keep up with a thorough turnaround programme thereafter.

• Once the chicks are housed all visitors should be kept to a minimum for the first six weeks, and a good bio-security programme should be adhered to. Overalls, boot covers and the use of foot dips (regularly changed) should be enforced.

Finally, it is also important to bear in mind that if a producer has birds sent for PM and Marek’s is found, this does NOT necessarily mean that they will go on to experience high mortality. Marek’s is no different to any other disease in that there is always a possibility of it being found in one or two birds in a flock, normally in birds that are sick or underweight.

A THREE-WAY PARTNERSHIP

On a positive note, all the evidence indicates the Marek’s threat has now receded. Looking back on her own company’s experience, Olivia Potter highlights the need for co-operation between all those involved. "What is most important to remember is that defeating Marek’s requires a three-way partnership. The hatchery has a very important role to play in administering the vaccine effectively; the rearer has an equally important role in keeping a ’clean’ farm and observing chick quality; and thirdly, the egg producer also has a role to play in housing the pullets into a clean environment and keeping stress to a minimum."

DOUBLE VACCINATION

One of the recommendations listed above was double vaccination, and this is a practice that is gaining strong support within the industry. Olivia Potter describes it as a ’MUST’. "For the sake of the small extra cost, it is not worth the rearer or egg producer taking the risk," she says.

Steve Carlyle, of Country Fresh Pullets, is another firm advocate of double vaccination. Country Fresh began looking for new answers when, after many trouble-free years, they started seeing Marek’s. Breaks occurred at Free Range sites around three or four years ago, at first only at sites where a high challenge was to be expected, for instance where the young birds were in close proximity to layers. Tightening up on biosecurity seemed the appropriate solution; this was duly done and initially it appeared to have worked. But then, even with all the correct biosecurity in place, another break happened at an isolated site where there was no reason to suspect any significant level of risk. It was at this point that Country Fresh decided to switch to double vaccination – and since then they have experienced no breaks whatsoever. "Double vaccination seems to have been the solution for us. There is no question in my mind that it does bring a benefit. The one major change we made on the rearing farm is that we began double vaccinating all our litter chicks; that was two years ago, and since then we’ve never had a problem," says Steve. "It puts 3p onto the price of a pullet, and in my opinion this is a very small premium to pay for a very valid extra insurance.

"I realise that some rearers who have not yet had breaks are still sceptical, but I believe that more of them will recognise the need to adopt this practice in the future."

There are many in the industry who agree with Olivia and Steve; John Bowler, for instance, is already committed to the double vaccination route. Although there is as yet no clearcut explanation as to why double vaccination works, experience indicates quite clearly that it does, and work is being carried out on this subject. Sue Baigent, a BBSRC research scientist who specialises in Marek’s disease, has been involved in a very recent study carried out by Fort Dodge. Sue points out that when evaluating the results of any such study it must be borne in mind that with a single vaccination cycle there is always the possibility that a small percentage of chicks may not receive the full dosage – for instance if the needle is not positioned 100% accurately. Double vaccination would eliminate this risk as it is extremely unlikely that this would happen twice to the same chick. Her view is that in ovo vaccination is a more accurate technique, as the machine uniformly vaccinates a tray of eggs at once. Nonetheless, Sue does not discount the possibility that administering a second vaccination may provide an extra boost to the chicks.

RECENT STUDIES CARRIED OUT BY FORT DODGE

Herve Le Galludec, Poultry Business Unit Manager at Fort Dodge Animal Health, explains the background to the project. "We had been aware for some years that this ’double vaccination’ was done in some countries, and field exper