Mad Cow Found At Hanford, Calif. Transfer Station (VIDEO)

File photo of a cow.

HANFORD, Calif. -- A senior manager with a California rendering company said Tuesday a cow at its Hanford, Calif., transfer station tested positive for mad cow disease.

Dennis Luckey, executive vice president of Baker Commodities in Los Angeles, told The Associated Press the disease was discovered after workers selected the cow for random sampling.

The sample was taken from the dead cow's carcass on April 18 at a hide-removal site, he said.

"This animal happened to be one that we randomly selected," Luckey said.

The company does not yet know which farm the cow came from, but the animal never made it to Baker's rendering plant 50 miles away in Kerman, Calif., Luckey said.

On April 19, a lab at the University of California, Davis reported that its test on the sample was inconclusive, he said.

The sample was then sent on to the Agriculture Department, which confirmed on Tuesday that the cow is the fourth discovered in the United States to test positive for the disease.

Flip through the slideshow below for the history of mad cow incidences in the U.S. since the first case in December 2003:

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• December 2003: First U.S. Case Of Mad Cow Disease

  The <a href="http://articles.cnn.com/2003-12-23/us/mad.cow_1_mad-cow-disease-fatal-brain-wasting-disease-bse?_s=PM:US" target="_hplink">first confirmed case</a> of mad cow disease in the U.S. involved an animal from a farm in Mabton, Wash. The Holstein had been <a href="http://www.nytimes.com/2004/01/03/us/way-to-track-us-cattle-isn-t-ready-for-quick-use.html" target="_hplink">imported in 2001 from Alberta, Canada</a>, along with 70 other cows. The animal was a "downer," which means it was unable to walk when it reached the slaughterhouse, a condition that mandates automatic testing from the USDA. Following the determination of mad cow, the processor, Vern's Moses Lake Meats, voluntarily recalled 10,410 pounds of raw beef amid concerns that products might be tainted. These cows, pictured at Sunny Dene Ranch in Mabton, were quarantined in the following months during an investigation.

• June 2005: Second Confirmed U.S. Case

  The second confirmed occurrence of the disease in the U.S. was linked to a farm in Texas, though it appears to be the country's first home-grown case. <em>The New York Times</em> reported that the animal was about 12 years old at the time of its death. It had spent the <a href="http://www.nytimes.com/2005/06/30/national/30cow.html?" target="_hplink">entirety of its life</a> on the same Lone State ranch until it was taken to pet food plant Champion Pet Food, Inc. in Waco, Texas, where it died in November of 2004. The animal was a "downer" which pet food outfits often take since the USDA prohibits such cows for human consumption. Testing for disease is still mandatory, and meat from the animal did not enter the food supply, thanks to safeguards. <em>Photo by Flickr user <a href="http://www.flickr.com/photos/mdenhoedt/4627140451/sizes/z/in/photostream/" target="_hplink">MdenHoedt</a>.</em>

• March 2006: Third Confirmed U.S. Case

  A cow in Alabama was the third confirmed case of mad cow in the U.S. CBS reported that USDA head veterinarian John Clifford assured the public that meat from the animal <a href="http://www.cbsnews.com/2100-201_162-1396022.html" target="_hplink">had not entered the food supply for people or animals</a>. The animal was also a "downer," which led to it being euthanized and tested. <em> Photo by Flickr user <a href="http://www.flickr.com/photos/shan213/5293549136/sizes/l/in/photostream/" target="_hplink">Shan213</a>.</em>

• February 2012: First Reported Cases of Mad Cow In Humans Is False Alarm

  Earlier this year, <a href="http://www.huffingtonpost.com/2012/02/09/marin-mad-cow-disease_n_1266959.html" target="_hplink">two reported cases</a> of mad cow-related illness in Marin County, Calif., one fatal, turned out <a href="http://www.nbcbayarea.com/news/health/Mad-Cow-Didnt-Kill-Marin-Woman-Officials-139057459.html" target="_hplink">not to be linked</a> to the disease. The scare, however, leaves Americans shaken.

• April 2012: Fourth Confirmed U.S. Case

  The fourth confirmed case of the disease was <a href="http://www.huffingtonpost.com/2012/04/24/mad-cow-disease-california-usda_n_1449871.html?ref=food" target="_hplink">traced to a dairy cow</a> in central California.