SCIENTISTS have cracked the genetic code of sheep to reveal how they became a distinct species from goats around 4 million years ago, and the study is the first to pinpoint the genetic differences that make sheep different from other animals.
The International Sheep Genomics Consortium compared the sheep's genes with those of other animals, including humans, cattle, goats and pigs.
The analysis identifies several genes that are associated with wool production. It also reveals genes that underpin the evolution of the rumen.
This collaborative study, involving 26 research institutions in eight different countries, was led by researchers from the Commonwealth Scientific & Industrial Research Organization (CSIRO) in Australia, BGI and the Kunming Institute of Zoology in China, Utah State University and Baylor College of Medicine in the U.S. and The Roslin Institute in the U.K.
Professor Alan Archibald, head of genetics and genomics at The Roslin Institute, said, "Sheep were one of the first animals to be domesticated for farming and are still an important part of the global agricultural economy. Understanding more about their genetic make-up will help us to breed healthier and more productive flocks."
The research identifies the genes that give sheep their fleece and uncovers features of their digestive system that make them so well-suited to a diet of low-quality grass and other plants.
The rumen, which is thought to have evolved around 35-40 million years ago, has the ability to convert lignocellulose-rich plant materials into animal protein.
Wool is the most economic feature of sheep, while the synthesis of wool is supposed to be linked to fatty acid metabolism. The genome data yielded in this study will lead to a better understanding of all of those unusual evolutionary traits of sheep, BRI said.
The rumen is differentiated from the true stomach by its tough, keratin-rich surface, which is very similar to skin, CSIRO explained.
Many genes normally expressed in skin are also highly expressed in the rumen, but a number of new genes were identified that are specific to the rumen, as well as one that appears to be present in most mammals but has so far only been expressed in ruminants, the Australian research agency noted.
"We investigated the completed genome to determine which genes are present in a process called gene annotation, which resulted in an advanced understanding of the genes involved in making sheep the unique animals that they are," CSIRO project leader Dr. Brian Dalrymple said.
"Given the importance of wool production, we focused on which genes were likely to be involved in producing wool. We identified a new pathway for the metabolism of lipid in sheep skin, which may play a role in both the development of wool and in the efficient production of wool grease (lanolin)," he added.
Min Xie, project manager from BGI, said, "Sheep are an important livestock with great economic value to provide people with meat, milk and fine wools. The availability of the sheep genome provides us an opportunity to investigate the genetic basis of the rumen evolution and lipid metabolism in sheep skin. Based on the genomic data in this study, more and more sheep-related studies could be conducted for expanding our understanding on this livestock. It also facilitates the maker-assisted selection for high-quality traits such as wool, meat, milk, among others."
The genome builds the most complete picture yet of the sheep's complex biology. Further studies using this resource could reveal new insights into diseases that affect sheep.
Sheep are also an important biomedical model, particularly in Australia, and the genomic resources built by the team will provide a strong foundation for the detailed exploration of the similarities and differences between sheep and humans at the molecular level and hopefully lead to improved medical treatments for a number of conditions such as sepsis and asthma.
This work will accelerate research on all kinds of sheep traits — from reproduction and lamb growth to wool quality, milk yield, methane production and disease resistance, the American Sheep Industry Assn. (ASI) said in an announcement, and these applications may lead to better breeding strategies and new approaches to sheep management.
"The availability of the genome assembly will improve the efficiency and timeliness of genetic and genomic studies in sheep," said Noelle Cockett, Utah State University provost and professor in the department of animal, dairy and veterinary sciences. "I anticipate an increasing number of discoveries coming out of the assembly that will translate into improvements for the sheep industry."
ASI president Clint Krebs added, "The publication of this discovery dawns a new day for sheep production in the U.S. and globally. Besides bringing to light a better understanding of basic biology, the opportunities for improvements in production efficiency of lamb and wool, plus health and disease management, are almost limitless."
The study was published June 5 in the journal Science.