Unscrambling genetics of chicken's blue egg

Unscrambling genetics of chicken's blue egg

RESEARCHERS at The University of Nottingham in the U.K. have discovered the chicken genetics that cause eggs from some breeds to be "blue" — an egg color that some call the "latest foodie fashion" because those eggs may be "tastier and cleaner breaking" than more traditional brown or white eggs.

In a four-year research project published recently in the journal PLOS ONE, the team from the University of Nottingham School of Biology identified the genetic mutation that first produced the blue egg in a native South American chicken, the Mapuche fowl, and their European descendants, Araucana, between 200 and 500 years ago. The results could inform future research into agricultural breeding techniques if demand for blue eggs continues to grow.

The researchers used the unique genetic resources conserved by heritage poultry breeders to identify, at fine resolution, the exact location of the mutation in the genome in blue egg-laying chickens.

This work was followed by a further genomic study that revealed the genetic cause of the blue-colored egg shell: an ancient, harmless retrovirus in the domesticated chicken.

The researchers explained that a retrovirus is a virus that, unlike most cellular organisms, carries its genetic blueprint in the form of ribonucleic acid (RNA). It reproduces itself in a host cell using a special enzyme called reverse transcriptase that transcribes RNA into deoxyribonucleic acid (DNA). This makes it possible for genetic material from a retrovirus to become permanently incorporated into the DNA of an infected cell.

In this case, the effect of the retrovirus is to trigger an accumulation of a green-blue bile pigment called biliverdin in the eggshell as the egg develops in the hen.

"An unexpected find was the unique integration sites for the retrovirus in South American/European and Asian chickens. It shows the importance of viruses in shaping evolution and diversity of species," said team leader David Wragg, a doctoral research fellow with the Biotechnology & Biological Sciences Research Council (BBSRC). "It's quite remarkable. Retroviruses are generally considered to integrate at random locations in the genome, and so the chance of a retrovirus integrating at more or less the same location in two chicken populations is extremely low. Moreover, when appearing in the population, the unusual egg coloration must have attracted the attention of the owners, who must be praised for having selected the trait in subsequent breeding."

Color diversity. The work was initiated by professor Olivier Hanotte, whose curiosity about blue eggs was sparked on a trip to Brazil, where he met professor Jose Antonio Alcalde, co-author of the paper.

Alcalde said, "This is an important discovery because some of these rarer native breeds of chicken with this unusual egg color and high quality have become low in number and are in danger of disappearing if not conserved and indeed promoted by agriculture."

Significantly, the same findings have also been independently discovered and reported by a research group in China that has examined local Chinese and North American breeds.

The University of Nottingham research was carried out with the help of scientists from Universidad Catolica de Chile, Institut National de la Recherche Agronomique in France, the International Livestock Research Institute in Kenya, the Chinese Academy of Agricultural Sciences in China and the University of Sydney in Australia.


Chick prebiotics

Feeding young broiler chickens a prebiotic yeast supplement could have positive effects on their development and increase their defenses against gut infections, according to research funded by BBSRC and animal nutrition company Alltech U.K.

Researchers from Nottingham Trent University fed 240 broiler chickens differing doses of a yeast-based feed supplement and monitored them every day for 42 days. Except for their feed, all other conditions were identical.

According to BBSRC, the findings suggest that a feed supplement containing a carbohydrate found in yeast resulted in the birds having greater natural defenses to harmful bacteria entering their guts and that younger broilers gained the most benefit from the supplement.

Lead researcher Harriet Lea, a BBSRC-funded student based in the Nottingham Trent School of Animal, Rural & Environmental Sciences, explained, "There are several non-antibiotic feed supplements on the market, but there is a real need to understand how exactly they support gut health in chickens so that farmers have a better chance of increasing their efficiency and improving flock welfare."

The research, published in the Journal of Applied Animal Nutrition, suggests that the benefits of yeast supplement (Actigen) could be age dependent, with younger birds having a greater storage capacity of mucin (a substance secreted by the gut lining that can help defend against infectious agents).

The natural carbohydrate fraction investigated is a feed supplement that is already used in some commercial broiler diets, but there is uncertainty as to how it works. Although the supplement is likely to work through several mechanisms, these findings help clarify how the supplement improves the immune defenses of the bird through altered mucin production, BBSRC said.

These new findings may lead to more widespread use of yeast-derived supplements in broiler feeds to improve gut health and immunity.

The next stage of the project is to investigate the effects of this carbohydrate fraction on gene expression of the bird to investigate, at a molecular level, how the supplement induces changes in bird development and gut health, Lea said.


Egg yolks

While some are focusing on the color of the egg shell, other researchers are looking at the color of the yolk, which is an important quality trait.

In abstract 25 presented at the recent Poultry Science Assn. meeting, Y. Loetscher, M. Kreuzer and R.E. Messikommer of ETH Zurich in Switzerland suggested that plant-derived additives like tagetes petals are "an interesting alternative to synthetic pigmentation," especially in organic production.

Unexpected coloring effects nettle has on broiler skin suggest that this plant could be a cost-efficient coloring agent as well, Loetscher et al. said.

Noting that natural additives often affect lipid oxidation, Loetscher et al. investigated the effect of adding nettle to feed on yolk yellowness and oxidative stability in laying hens.

The researchers fed a wheat-based, balanced diet to forty 70-week-old H&N Brown Nick layers. The diet did not include tocopherols or corn to ensure low dietary antioxidant and pigment levels.

All hens were fed the basal diet plus pigmentation (25 parts per million Carophyll Yellow and 15 ppm Carophyll Red) for two weeks. In the four-week experimental period, the effect of three nettle dosages (6.25, 12.50 and 25.00 g/kg) from two batches were compared with a negative control (basal diet only) and a positive control (pigmentation and 40 ppm alpha-tocopherylacetate).

Egg quality traits and yolk color (L*, a*, b*, color space) were measured. Susceptibility to lipid oxidation was evaluated in lyophilized yolk powder stored at 20 degrees C in weeks 0, 4, 8 and 12 of storage.

According to Loetscher et al., experimental feeding had no effect on egg quality traits such as shell stability, egg weight and Haugh units. Yolk yellowness (b*) was lowest (P > 0.05) within the negative control (18.3). The b* values of all nettle treatments (average 30.3) were equal to the positive control (29.4). Batch differences were only detected between the two batches fed at the 12.5 g/kg dose (24.6 versus 31.6), the researchers said.

In week 12, lipid oxidation in egg yolk powder was highest (P > 0.05) for the first batch fed at 12.5 g/kg (29.5 mg MDA/kg) and lowest (P > 0.05) for the positive control (7.9 mg MDA/kg) compared with the negative control (18.3 mg MDA/kg) and intermediate values for all other groups (average 17.2 mg MDA/kg).

Even adding the lowest dosage of nettle to layer feed was sufficient to intensify yolk yellowness equal to or better than synthetic pigmentation, Loetscher et al. concluded.


Hen housing

Public concern about the welfare of hens kept in conventional cages has become an important issue worldwide.

At the Poultry Science meeting, J.Y. Hu of Purdue University, H.W. Cheng and R.L. Dennis of the U.S. Department of Agriculture's Livestock Behavior Research Unit and W.K. Fulwider of the Organic Valley CROPP Cooperative reported on a study that examined the effects of conventional cages and floor pens on hen health and egg production (abstract 76).

Hu et al. randomly assigned 84 nineteen-week-old Bovan Brown hens into one of 12 two-bird cages — each providing 968 sq. cm of floor space per hen — or into one of six 10-bird floor pens — each providing 3,711 sq. cm of floor space per hen — for eight weeks.

The floor pens were furnished with perches, nest boxes and wood shavings.

Egg production was recorded up to 27 weeks of age. Egg weight, egg quality and shell quality were measured at weeks 23, 25 and 27. Plumage condition, foot health, mineral density of the tibia, femur and humerus and the heterophil:lymphocyte (H:L) ratio were evaluated at week 27.

According to Hu et al., daily egg production, plumage condition and feet hyperkeratosis of hens were not affected by the housing environment (P > 0.05). The mean claw length of caged hens was longer, at 1.11 cm (P < 0.0001), than those housed in floor pens, which was 0.87 cm, the researchers said.

At 23 weeks of age, caged hens had a greater egg weight (P = 0.001) of 62.65 g and larger width (P = 0.001) of 44.28 mm compared to floor pen-housed hens, which had a 57.83 g egg weight and 42.99 mm egg width, Hu et al. reported. However, the floor pen-housed hens had higher shell mass at 23 weeks of age (P = 0.001). Floor pen-housed hens also had greater bone mineral density in all three examined bones than that of the caged hens (P = 0.002).

The H:L ratio, an immunological response parameter and stress indicator, was higher (P = 0.002) in caged hens, at 3.76, compared to floor-housed hens, at 3.32, Hu et al. noted.

Overall, the results suggest that furnished floor pens may be a favorable alternative housing system to conventional cages for improving hen welfare; however, the cages still have certain advantages for egg production, Hu et al. concluded.

Aviary systems. Aviaries provide tiered cages and daytime litter access to laying hens, but little is known about movement throughout this system and the use of the litter resource throughout the day, D.L.M. Campbell, J.M. Siegford, M.M. Makagon and J.C. Swanson of Michigan State University explained in abstract 77.

Campbell et al. conducted a study in a commercial aviary barn as part of the Coalition for Sustainable Egg Supply project to evaluate numbers of hens exiting and entering a tiered cage unit, using closed litter areas underneath the aviary unit and out on the open litter area, as well as the frequency of piling behavior (i.e., hens clustering together).

Data were collected via video from eight of 40 aviary sections in one barn over one day each when hens were 27, 52 and 77 weeks of age, Campbell et al. said.

Total numbers of hens exiting and entering the cage unit as well as total numbers moving underneath the unit and returning to the open litter areas were counted over six 30-minute time periods. Numbers of hens on the open litter area were counted every 15 minutes over three 2-hour time periods throughout the day. All occurrences of piling were documented, describing total duration and peak size.

The most hens moving both in and out of the unit (P < 0.0001) and between open litter and under the unit (P < 0.0001) were observed in the morning following aviary opening, Campbell et al. reported. The largest number of hens seen in the open litter area was between 3 and 5 p.m. (P < 0.0001), and the piling duration ranged from two minutes to four hours, with the peak size of individual piles ranging from 10 to 125 hens, the researchers added.

Volume:85 Issue:35

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