Ken Randall reports from the recent training programme at Reaseheath College on strategies for successful vaccination
The secret of successful on-farm vaccination is thoughtfulness, conscientiousness and consistency, according to Alastair Johnston of the Minster Veterinary Practice.
Allied to that, success or failure was “80% preparation and 20% execution,” he told the Reaseheath College vaccination workshop.
The reasons for vaccinating went beyond just protecting birds from specific clinical or sub-clinical infectious diseases.
Vaccines could also reduce the impact of immunosuppressive diseases, and improve flock performance in terms of body weight, FCR, egg numbers and egg quality.
They could also reduce vertical transmission and provide maternal immunity in youngstock. And they played an important role in preventing the transmission of disease to humans.
The penalties for poor technique were considerable. If vaccination was not done correctly, it was likely to give little protection against disease.
There was also a danger of rolling vaccination reactions, possibly creating respiratory problems, poor performance and increased rejections.
Successful vaccination was reliant on good preparation, timing and technique, combined with healthy and stress free birds. Just as important was to use appropriate, good quality vaccines.
The choice of vaccine used should depend on the disease history of the site and its locality, the national disease status, plus cost and availability.
The actual vaccine policy should be reviewed regularly with the vet, not only covering which vaccine to use, but the age at which to carry it out and the method of administration.
General recommendation were always:
• Order vaccine with plenty of time
• Check use-by dates, numbers of doses and vials
• Ensure vaccine is transported and stored correctly
“Never cut vaccine doses to save money, always use the correct number for the birds in each house,” Mr Johnston advised.
Live vaccines should be stored at between at 4-8C – not too warm, not too cold. A fridge that formed ice deposits inside was set too low, he said.
Poultry vaccines came in the form of live infectious bacteria or viruses, which had been altered or attenuated; and inactivated or dead ones.
Live vaccines would give a rapid response, with antibodies produced either locally in the tissues, or in the blood, or in cells.
The agents in the vaccine had to be alive when reaching the host, so that they could reproduce themselves, and enough must reach each host to stimulate a protective response. Ideally every bird should receive one protective dose of vaccine.
An important characteristic of live vaccination was the spread of the “infection” from bird to bird, and it was vital for all birds to receive the initial dose, rather than catch the first exposure from another bird.
“How well a vaccine works depends on the quality of administration. If only some of the birds receive vaccine, the result is that vaccinated birds will shed virus a few days later and infect the remaining birds.
“This ‘rolling challenge’ of vaccine virus mimics a field challenge and can make the birds snick as well as aggravate any field challenge.
“If birds get their dose from other birds, they can get it in a nasty way. Virus vaccines tend to ‘hot up’ as they circulate through the birds.”
If birds showed signs of coughing, loose droppings or a drop in egg production after administration, the vaccination was not done as effectively as it should have been.
The two principle methods of on-farm vaccination were by drinking water and by spray.
Drinking water vaccination had the advantage of low labour cost, less stress on the bird and no extra equipment. There were significant disadvantages, however, which included inconsistencies in water uptake, inadequate water quality and a high miss rate.
“It is not as simple and fast as it is thought to be,” said Mr Johnston. “The procedure requires a lot of mental and physical preparation.”
Live vaccines needed to be kept alive long enough to work, which entailed rapid distribution and protection from inactivating agents.
They were also susceptible to ultraviolet light, heat, heavy metals, organic matter, moisture and sanitisers. Once reconstituted with diluent, they lasted about three to five hours.
Mains water contained chlorine, while bore hole water might contain heavy metals or calcium. Low-fat skimmed milk powder or water conditioners could be used to fully protect the vaccine, Mr Johnston advised.
Vaccine response relies on a healthy immune system, and is less effective in birds that have been compromised systems. This can be caused by a wide variety of factors, the foremost of which is stress, usually caused by poor environment, nutrition or management. These lead to increased levels of cortisone hormone in the blood, making the immune system inefficient.