Genomes for Agriculture

One of the most important things for agriculture that happened the past year not mentioned in the usual farm papers was the arrival of several farm animal genome studies. The one nearest to most of us is the genome of the cow, published in the journal Science for the 24th of April, 2009.

Cattle, Bos taurus (European type cattle) and Bos taurus indicus (India derived breeds) are not closely related to humans in their genetics, compared to many other species. They are specialized for converting low-quality forage into energy dense fat, muscle and milk. They were domesticated 8,000 to 10,000 years ago in the Near East. There are presently about 800 breeds. This variability allows study of genetic and variable traits, including milk production economic gain and tenderness. The most detailed sequencing was done on a Limousine, with comparison to other breeds.

They have 26,835 genes, somewhat more than humans, including about 22,000 genes responsible for coding proteins. It was observed they have many more genes for lactation and immunity than humans. The greater number of immunity genes may be the result of the huge number of different microorganisms in the rumen (which present greater opportunities for infection) or due to the herd life habit of cattle. Another important difference is that in humans passive immunity is gained by placental transfer, but in cattle it occurs by ingestion of immunoglobin IgG in colostrum. Core metabolism is very similar among all mammals

A second article in the same issue studied genetic variation in breeds. It conclude that variation was at least a great in cattle as in humans, in spite of constraints imposed by domestication and breed development. European and indian type cattle diverged 250,000 years ago and the Indian type have somewhat greater genetic diversity. European breeds are now so standardized they might have been breed from 200 to 300 cattle 200 years ago. This is believed to be to breed selection pressures and subsequent selection for milk or beef. Loss of diversity should be of concern to animal breeders, the authors suggest. Statistical evidence shows some of the highest selection pressure was in the genes affecting double muscling, milk yield and composition and intra- muscular fat content.

The genome of the horse, Equus caballus, was published in November. The horse was tremendously important most of recorded history for transportation, draft animals and for warfare from before the time of Alexander the Great to World War II. It is now primarily relegated to recreation, but is of interest to science and medicine because so many of the diseases of man also occur in horses.

Horse DNA is more similar to human than Cattle DNA, and we share many communicable diseases and at least 90 hereditary diseases with them. The most detailed sequencing was done on a Thoroughbred with comparisons to most of the world’s other horse breeds, including American quarter horse, Andalusian, Arabian, Belgian draft horse, Hanoverian, Hakkaido, Icelandic horse, Norwegian fjord horse and Standard bred. The horse genome is smaller than the cattle and human genomes, but larger than the dog genome. One of the remarkable characteristics of the horse genome is how few chromosomal rearrangements there are between it and the human genome.

A second article shows that horses were domesticated in and around Kazakhstan some 5500 years ago. Colors developed rapidly after domestication as the result of selective breeding by ancient farmers.