An alley for processing animals such as cattle or buffaloes is described which includes a pair of spaced-apart alleys at the entrance end of the alley and a single alley at the exit end of the pair of alleys at the entrance end of the alley. The outer side walls of the alleys are easily adjusted to vary the width thereof thereby enabling the alley to accommodate animals of different sizes. Rear-up prevention device mechanisms are also provided in each of the alleys to prevent the animals from raring up and falling over backwards. The alley may be either portable or stationary.