The pilot was engaged on cotton spraying operations. During the second take-off for the day from this particular strip, a cow ran in front of the aircraft. The pilot attempted to fly over the top of the animal, however the left maingear struck and killed the cow. The pilot was able to maintain control of the aircraft, and diverted to a more suitable aerodrome, where a landing was made without further damage. The strip in use was not fenced to prevent the entry of stock, which had not caused problems in the past. Since the accident the property owner had installed suitable fencing.