Going back to the original posting (which I can't believe I missed!) the only British Army mountain gunners were the TF group, 4th Highland (Mountain) Brigade, RGA. Other mountain gunners were Indian Army gunners who used mules for transport. Before and after the brigade was mobilized they used Highland Ponies. When they were posted to the 29th Division for Gallipoli, they suffered losses and these lost ponies were replaced by mules. By the time they had fought in Egypt and moved to Salonika in August 1916, all of the animals were mules.