David Holdsworth's wildlife photos, Kenya, Feb 2009
 

For the nomadic Masai people, cattle is the most valuable and important thing they own. Traditionally, they don't grow crops or even do much hunting. Their entire way of life revolves around their herds of cattle.
The Masai get nearly all of their food from their herds of cattle, in the form of either milk or meat. Though they do drink the blood as well, it's not really something that's done as a regular meal-time event. They generally don't hunt or grow their own crops. The cattle are literally their bread and butter. In each village, the cows are protected and herded by the men, but the milking is done by the women.
Because of their importance, the Masai use cattle as their form of currency and wealth. On average, each individual of the Masai tribe owns around 15 head of cattle, which makes these people among the wealthiest in Kenya, if a dollar value was placed on their herds. Cattle change hands for any major transaction, specifically when a warrior seeks to marry. He must pay a bride price in cattle.
After generations of stealing cattle from other tribes, the Masai cattle are not strictly one particular breed. Their cows are quite a mixed bag. Along with their herds of prized cows, the Masai also keep other livestock, like goats and sheep. The Masai are very observant with their cows and can recognize each one by their colour and body shape. Some groups use cuts on the cows' ears to help identify them.
Large chunks of their land were taken by the Kenyan government to create large game preserves, such as the Nairobi National Park, the Masai Mara game preserve, and the Serengeti National Park. So with less land, the Masai have less room to roam their cattle.