Different animals. However Water Buffalo from colder climates is still said to produce better horn.
Remember that the horn used for composites back in the day probably came from Buffalo being bred in the area where the bows were used. Water Buffalo have been in more Northern regions for hundreds if not thousands of years.
From Wikipedia:
European buffaloes are all of the river type and considered to be of the same breed named Mediterranean buffalo. In Italy the Mediterranean type was particularly selected and is called Mediterranean Italian breed to distinguish it from other European breeds, which differ genetically. Mediterranean buffalos are also found in Romania, Bulgaria, Greece, Albania, Kosovo and Republic of Macedonia, and a few hundred in the United Kingdom, Germany, the Netherlands, Switzerland and Hungary. There has been little exchange of breeding buffaloes among countries, therefore each population has its own phenotypic features and performances. In Bulgaria, they were crossbred with the Indian Murrah breed, and in Romania some were crossbred with Bulgarian Murrah.[12] Populations in Turkey are of the Anatolian buffalo breed.[
