Traditional strains of chicken may not have a place in the modern poultry house, but they could hold the key to some future advances in breeding. Take the case of the Hellevad chicken, little known outside a remote corner of Denmark until it was found to contain a gene that seems to be linked to robust health.
By Roger Ranson , BHR Communications, UK
The Hellevad chicken is an egg laying strain that has been bred by the Wolf family over the past 50 years and sold to small producers, many of them backyard or hobby farmers, in small numbers. The hatchery, in the northern part of Jutland, has a capacity of hatching 3,000 day-old chicks at a time, and sells some 35,000 pullets during the year.
The breed is a combination of original US and native Danish blood lines. The female line is derived from the New Hampshire breed imported to Denmark in the 1950s, while the male line is a local strain of white Leghorn developed by the Skalborg breeding centre over 30 years and then acquired by the Wolf family in 1980. This was a pivotal moment in the Danish egg industry, a year after the Government lifted the ban on battery cages. This led to the widespread adoption of international hybrids, lighter strains selected for cage production, and the demise of many native breeds.
The customer base of the Hellevad hatchery, far removed from the large-scale commercial industry, enabled it to continue developing its traditional strains for the local market, particularly the organic and free range sectors that account for more than 15% of the Danish demand today. Hatchery owner Jørn Wolf has always known that his layers enjoyed robust health. They have been given no preventative medication or treatment for 45 years, have low mortality and retain good feather cover throughout lay.
In a 1997 trial against a commercial ISA layer strain, the inferior egg production of the Hellevad breed was balanced by much lower mortality as a result of the more docile behaviour as well as disease resistance. This characteristic attracted the interest of research scientists at a Government institute. The Faculty of Agricultural Sciences, Aarhus University, has an institute near Viborg where senior scientist Dr Helle Juul-Madsen and her colleagues work on immunology. “No, there’s no connection between my name and that of the hatchery,” she quips as she introduces their work to us.
Improving immune system
The current focus of their work is a protein called mannose-binding lectin, MBL as it is usually termed, which is known to play a role in improving the immune system. It is used in human medicine for treating cancer patients who have a weakened immune system due to a genetic defect in their MBL gene while recovering from chemotherapy.
The researchers were astonished to find the MBL level in the Hellevad strain two to three times the normal level in commercial egg layer breeds. “Ten years ago we took part in a project collaborating with organic farmers who used this breed to produce eggs for the Danish market,” says Dr Juul-Madsen. “At the same time, we ran a project selecting experimental birds for low or high concentrations of MBL in the blood. We wanted to analyse the relation between MBL and disease resistance in chickens since it was already known that genotypes causing low MBL level in humans are associated with many different diseases. So we decided to test a number of commercial egg layer strains used in Denmark for their basic level of MBL and found that the Hellevad chicken had two to three times as much MBL in the blood as other commercial egg layers.”
They have investigated the role of MBL in fighting disease, seemingly activating the natural defence mechanisms to destroy not just one kind of pathogen but viruses, bacteria, fungi and parasites. The MBL protein has developed a reputation as a ‘pathogen detector’ binding to mannose and other sugars on the surface of the pathogen and triggering the immune system. This leads, for instance, to bacteria cell membranes being punctured, phagocytosis which ‘gobbles up’ bacteria and viruses, and other destruction mechanisms.
“It is so effective in enhancing the innate immune system that it has even been called the miracle protein,” says Dr Juul-Madsen. “People with a genetic defect, making it impossible for them to produce functional MBL, are very susceptible to infections especially before the age of two when the immune defence system is not fully developed. If those children are injected with purified MBL, they will recover more easily from infectious diseases.”
Four year project
Now she and her colleagues are poised for a major expansion in their work through winning a grant from the Danish Council for Strategic Research and financial support from Cobb-Vantress. The four-year project costing 18.160 million Danish Krone (US $3.42 million dollars) has attracted a grant of almost 12 million D Kr from the Danish government and 2.7 million D Kr from Cobb. It has become known as the Poly-Reid project, a form of acronym from the plan to target polyvalent resistance to infectious diseases.
The project, which includes funding one post doctorate position and two PhD studentships, will focus on genotyping to identify the gene or combination of genes responsible for MBL levels.This aspect is particularly significant for Cobb which is working to enhance the innate immune system of its products as one of the targets of its genomic research program, according to Dr Mitch Abrahamsen, vice president of research and development.
Not yet fully sequenced
Cobb is determining the MBL genotypes of its pure lines but a comprehensive understanding of the genes regulating the chicken innate immune response is far from complete. More than 20,000 chicken genes have been mapped but there are still areas of some chromosomes, thought to be around 5% of the “good stuff” where the DNA has not been fully sequenced. The Danish work has already targeted DNA sequences which are thought to be linked with MBL levels. The scientists are searching for changes in the DNA coding, one difference in the sequence of nucleic acids termed the single nucleotide polymorphism (SNPs), that represent alternative forms, or alleles, of a gene. Then the link with a particular trait or phenotype, has to be validated. The secret to MBL levels could lie within the gene itself, or perhaps that part, the promoter region, which controls the switching mechanism that turns on the expression of a gene into a particular enzyme or protein.
The project will establish the MBL levels in the Hellevad parent lines and whether there is a sex linkage. For Cobb the prime interest is validating the role of MBL in enhancing immunity against diseases such as salmonella and E. coli, monitoring MBL in its pure lines and selecting for higher levels. “We’re excited to be involved in this project as the continual improvement of the innate immune system in our commercial broilers is a key focus of our R&D,” says Dr Abrahamsen. “The demonstrated experience and expertise of Dr Juul-Madsen and her research team was a critical factor in determining our desire to participate, and bodes well for the success of the investigation.”