Bulls...t
From Bukhari Vol. 4, #540
Narrated 'Abdullah bin 'Umar: Allah's Apostle ordered that the dogs should be killed.
From Abu Dawud #2839
Abd Allah B. Mughaffal reported the apostle of Allah as saying: Were dogs not a species of creature I should command that they all be killed; but kill every pure black one.
The Hadith's note for #2839 says, "The prophet did not order the killing of all the dogs, for some are to be retained for hunting and watching. He ordered to kill the jet black ones. They might be more mischievous among them.
From Muslim #3814
Ibn Mughaffal reported: Allah's messenger ordered the killing of dogs and then said, "what is the trouble with them (the people of Medina? How dogs are nuisances to them (the citizens of Medina)? He then permitted keeping of dogs for hunting and (the protection of) herds. ...[and for] for the protection of cultivated land.
From Muslim #Number 055
Ibn Mughaffal reported: The Messenger of Allah ordered killing of the dogs, and then said: What about them, i. e. about other dogs? and then granted concession (to keep) the dog for hunting and the dog for (the security) of the herd, and said: When the dog licks the utensil, wash it seven times, and rub it with earth the eighth time.
From Muslim #3813
Abu Zubair heard Jabir Abdullah saying: Allah's messenger ordered us to kill dogs and we carried out this order so much so that we also killed the dog roaming with a women from the desert. Then Allah's apostle forbade their killing. He said: "It is your duty to kill the jet-black (dog) having two spots (on the eyes) for it is a devil.
More here
http://www.answering-islam.org/Silas/dogs.htm
Those examples are from hadith, all written after Big Mo died.