Immunology and Disease Discussed at WPSA UK Meeting

Three papers on very different topics were included in an interesting session on Immunology and Disease at the annual meeting of the UK Branch of the World's Poultry Science Association (WPSA) earlier this year, writes ThePoultrySite editor, Jackie Linden. The topics included foot pad dermatitis, red mite control and Marek's disease.

17 June 2009

5 minute read

Factors Affecting Foot Pad Dermatitis in Turkeys

Foot pad dermatitis (also known as pododermatitis) causes economic losses through downgrading and carcass condemnations and leads to welfare concerns. It has been reported previously that poor litter management is a major contributory factor in inducing foot pad dermatitis in commercial turkeys, and two researchers in Scotland reported on their investigation to gain further understanding of this relationship.

The latest work at the University of Edinburgh into the effects of age of bird and litter moisture on foot pad dermatitis in turkeys was reported by Wu and Hocking. They confirmed that litter moisture is an important factor in causing food pad dermatitis by the highly significant differences in foot score in 28-day-old female turkeys that has been kept on litter of different moisture contents from six days of age.

In a second experiment, the researchers foot-scored turkeys at intervals up to 11 weeks of age, comparing those kept on dry litter with those on wet litter. At all ages (7, 21, 42 and 70 days) when the feet were studied, those birds on the wet litter had higher scores – indicating more or worse lesions – than those on the dry litter. Furthermore, the scores of birds kept on dry litter showed a tendency to improve over time, while those on the wet litter deteriorated with age.

Thyme Oil Shows Promise as Red Mite Treatment

Red mites (Dermanyssus gallinae) have become a significant nuisance, especially on egg farms in recent years, as the industry has moved away from battery cages and the number of permitted synthetic pesticides has dwindled. At the same time, consumer demand for food produced in an environmentally friendly manner is growing.

Scientists at the School of Agriculture at Newcastle University have been investigating alternative methods to control red mites for some time, and certain essential oils have shown promise. However, concerns have been raised over the possibility that these natural compounds may cause taints in the eggs that would make them unacceptable to consumers.

Smith and colleagues reported their latest results to the WPSA meeting, in which they treated layer houses with thyme or pennyroyal essential oils, and presented the eggs to a taste panel comprised of consumers. The levels used in the treatments were five times those previously found to be effective in killing the mites; a control without any active ingredient was included.

Before the test, all eggs were tested with a gas chromatography mass spectrometer to help identify possible taints. The results did not identify any essential oil compounds as being present in eggs laid by hens under the experimental treatments.

Consumers were able to detect the pennyroyal oil and found it unpleasant so the authors commented, "This oil would not be suitable for use as a D. gallinae acaricide where laying hens were present in the poultry house."

However, consumers did not detect any unpleasant taint in the eggs from the house treated with thyme oil.

"The results suggest that it should be possible to deploy thyme essential oil for D. gallinae management with no risk of egg taint influencing consumer attitude towards eggs and egg purchasing," concluded the researchers.

Model for Marek's Disease Developed

In the introduction to their paper, Nath and Bishop stated, "Marek's disease (MD), caused by a herpesvirus, is a very infectious, lymphoproliferative and chronic disease of poultry."

They went on to explain that it is possible to improve resistance to MD, which has been associated with MHC haplotypes, QTL and candidate genes but that incorporating this into a breeding programme is very challenging.

The scientists, from Biomathematics and Statistics Scotland and the Roslin Biocentre, used a compartmental model to describe transmission of the MD virus. The model was first described in 1992, for individuals moving from one state to another, and the present researchers applied it to the different infective phases of MD within chickens that had been vaccinated or remained unvaccinated.

Generally, the proposed model was effective in capturing the mechanisms of MD in both groups of birds. The researchers concluded, "With appropriate alterations of parameters, the present model of MD could be used for evaluation of different genetic and non-genetic strategies to control MD in poultry populations."