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The development game

Fundamental bioscience reveals useful insights into early wool and feather growth.

26 July 2011

Animals are complex beasts. They display a fantastic array of structures from horns to hair, feathers to fur. Animals look very different from one another and go about their business in very different ways, but the process of development links them together because for every animal, or indeed every organism, the journey to sophisticated adult begins with a single cell which divides, develops and differentiates according to a pre-programmed plan.

Studying that plan tells us not only how a ball of cells decides that an arm will be an arm and not antennae, but can provide insights into the development of traits in species important to agriculture, such as wool in sheep and feathers in chickens.

  The development game

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Understanding the fundamental biology of hair and feather growth may therefore underpin efforts to provide production gains or could contribute to improved animal welfare because knowledge from studying development can be applied using conventional breeding techniques to better suit farm animals to their environment.

Growth curve

Researchers at The Roslin Institute (RI) in Edinburgh, which receives strategic funding from BBSRC, are delving into the developmental genetics of wool and feather development.

"Development is also a fascinating process – easily the most interesting thing that happens on Earth," says Roslin researcher Dr Denis Headon. "Basically, embryonic cells grow into a ball and then use chemicals to signal to one another so that the blob of cells self-organises to make an eye, a leg, a brain and so forth, and matches the proportions of each of these body parts to give a functioning animal of whatever kind."

Headon adds that development defines the creature that will be born and has a lifelong impact; if this process goes badly wrong then it leads to congenital disorders that have serious detrimental effects on health.

Headon uses techniques such as in situ hybridization, which can highlight tissues where DNA or RNA is expressed. Here, activity of the hunchback gene is seen in Drosophila embryos at different developmental stages. Image: Nina

Headon uses techniques such as in situ hybridization, which can highlight tissues where DNA or RNA is expressed. Here, activity of the hunchback gene is seen in Drosophila embryos at different developmental stages. Image: Nina

Much of Headon's work is a fusion between genetics and developmental biology. His team maps genetic changes that cause altered phenotypes in wool, hair and feather characteristics, then identify the molecular nature of the mutation and analyse the function of the protein altered by mutation. "Genetics gives us a correlation between a trait and a specific sequence change in DNA, while the developmental studies give us a mechanistic insight into how the particular gene has an effect on development," he says.

In terms of the technology used, DNA sequencing and mapping are important, as is skin culturing and molecular biology. "Sometimes we also use mathematical modelling of cell communication to interpret our results and define experiments that need to be done," says Headon.

Headon's team also uses advanced skin tissue culture techniques so he doesn't need to work on live animals. Skin is removed from embryos as soon as they have developed a skin that is about to grow a hair or feather follicle. The skin is then bathed in a nutritious medium to maintain the cells, and the researchers manipulate cell-to-cell signalling pathways by adding defined doses of specific proteins or drugs which impair protein function. "Over a period of two days the feather or hair follicles will develop, and we can see the effect of a specific protein or drug on this process." This approach allows scientists to treat the skin with different reagents and not treat a whole animal, but the process does result in the destruction of some embryos.

Feathers developing in cultured duck skin. Image: D. Headon

Feathers developing in cultured duck skin. Image: D. Headon

The stuff of life

At first glance wool and feathers look very different but they are made of variations of the same stuff – keratin. Wool and hair (as well as fingernails) are made of alpha-keratins; feathers, scales and harder structures such as beaks are made of beta-keratins. "As far as we know, the molecules that control feather and hair formation are very similar," says Headon.

Wool and feather patterns are governed by similar developmental processes at their early stages. "Then as development proceeds the hair follicles and feather follicles diverge in appearance from one another," says Headon. "In mammals, hair follicles are produced across most of the body for a period as the skin is growing, while in chickens, feather follicles are produced in a specific wave that moves across certain regions of the skin. This wave leaves a very regular layout of feather follicles in its wake."

Headon says in the context of animal breeding, development is the process that defines the form of the animal. "So if we want to breed different forms, such as more or fewer feathers, then we need to understand this process." Headon's work is looking at natural genetic variations that impact on development so they can infom in conventional (rather than GM) breeding programmes to produce traits that are relevant and useful in agriculture and can address modern food security challenges.

Perfect knit

Take a bird's feathers for example. Too few feathers and skin can be irritated and damaged, reducing meat quality and representing a welfare concern; this can happen in meat birds (broilers) bred for large breast muscles that feathers may not adequately cover. Alternatively, too much feather cover makes birds susceptible to overheating in hot environments.

Transylvanian naked neck chickens were introduced into Britain in the 1920s. Image: D. Headon

Transylvanian naked neck chickens were introduced into Britain in the 1920s.
Image: D. Headon

And then there is the huge amount of feather waste produced each year by the 51Bn chickens slaughtered annually worldwide (ref 1). Hence, birds with reduced feathering are preferred in some places as they can tolerate higher temperatures, are easier to remove feathers from and produce less feather waste. "Naked necks are a good example of this," says Headon. "Overall, the idea is to understand how the skin produces feathers so that we can control this process by breeding to produce appropriate feather numbers for the type of bird and temperature conditions."

In the UK, sheep are now raised primarily for meat. Competition from synthetic fibres and natural textiles means that most British sheep breeds produce coarse wool of little economic value when shorn; high quality wools such as Merino tend to come from Australia.

Shearing, however, is still necessary each year to keep the animal healthy because a full fleece over the summer leaves animals susceptible to parasite attack and heat stress. Unfortunately for British farmers, due to competition from synthetic textiles the value of the fleece is less than the cost of having animals shorn, so UK farmers are collectively bearing a huge cost across the 30M sheep in the country (ref 1).

Wool is not worth what it was. Image: Powerhouse Museum Collection

Wool is not worth what it was.
Image: Powerhouse Museum Collection

Hence, breeding UK sheep with their Caribbean cousins whose fleeces fall off in summer, or British breeds such as Easy Care or the Wiltshire Horn, could result in a sheep that loses its fleece naturally in the summer, reducing the need for shearing and hence husbandry costs. This can be accomplished using conventional breeding because fleece shedding is natural to the ancestors of modern sheep – they were later bred to produce more wool in an age when it was worth so much more. "Quite a turn of events when you think that Britain's international economic power started with wool," notes Headon.

Headon's research demonstrates that fundamental development bioscience can impact factors affecting both animals and humans at local and global levels. "We are actively using mathematical modelling to gain a greater understanding of developmental processes in general and this will impact on human health and basic biology as well as animal health and production."


  1. FAO Stat (external link)
  2. Cryptic Patterning of Avian Skin Confers a Developmental Facility for Loss of Neck Feathering (external link)


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