Jan. 8, 2001 Australian scientists have located four genes involved in fat deposition in cattle that may offer new understanding of the problem of human obesity due to diet.
Researchers at Australia's CSIRO Livestock Industries think that how cattle deposit fat may help understand the process of fat buildup in individual humans.
"Humans and cattle are both mammals, and we share almost all our genes - although they are arranged differently on our chromosomes and have different gene sequences," says Dr Bill Barendse of CSIRO Livestock Industries.
"From our study of marbling in beef, we have located four genes which are important in why some animals become fatter than others, given essentially the same food.
"We see the same thing in humans - a rich diet will lead to obesity in some, and leave others skinny as rakes."
Marbling is the development of small flecks of fat throughout the muscle of cattle - and is a highly desirable trait in beef markets like Japan and the USA, because consumers associate it with high quality, flavour and tenderness.
Dr Barendse's team has been using DNA markers to predict the tendency of different animals to 'marble' - or put on fat within their muscle.
"Cattle are similiar to humans in one respect: fed the same diet, some individuals put on fat more readily than others.
"Most human obesity is due to overconsumption of a rich diet, not to large genetic mutations. Most experiments on obesity in mice don't help our understanding of humans, because obesity in mice is mostly due to genetic mutations rather than diet. This is what makes the cow so useful.
"Study of these genes will help us to understand how the process of depositing fat starts and proceeds - and thus, how we can modify it.
"In the case of feedlot cattle for the Japanese market, we want them to put on more fat within the muscle, and less fat on the outside. The sizes of fat deposits in different parts of the body are influenced by the genes. In the case of humans, we may wish to design personally tailored diets or treatments which help individuals to deposit less fat, or fat in different parts of the body."
The goal of the research program is to develop tests that allow cattle breeders to know the potential of their animals to develop marbling fat.
Dr Barendse says that the advantage of working with cattle is that scientists can study large numbers of animals, of known genetic background and fed on precisely specified diets.
"You can't do that with humans, because we all have different diets and different genetic backgrounds. But we hope that cattle will provide us with the model for a better understanding of our different abilities to become fat."
With support from Meat & Livestock Australia, Dr Barendse's team selected DNA markers from the cattle gene map. They collected blood samples, marbling data, carcase measurements and pedigree information on more than 4000 cattle, and used the DNA markers to locate the four genes most responsible for differences between individuals in how they deposit fat.
From this work they have developed a commercial test called the GeneSTAR Marbling test, which identifies a special variant of a particular gene called TG (thyroglobulin) that is strongly associated with marbling. Other tests are being developed.
"Animals which carry copies of this particular variant gene have a higher tendency to deposit fat within the muscle," Dr Barendse says.
"This gene is responsible for production of a substance called thyroglobulin. This is broken down into two thyroid hormones which strongly influence the body's metabolism and cause different kinds of fat cells to form and grow."
These thyroid hormones are common to fish, frogs, reptiles and birds as well as mammals and the way they function is well known.
For the beef industry, the development of genetic tests means that cattle producers can now test bulls - which are naturally lean - for their capacity to pass on the ability to deposit the right degree of marbling to their offspring. These end up as feedlot steers for export or premium grade domestic beef.
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The above story is based on materials provided by CSIRO Australia.
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