Pack mules care ammunition to front.
additional info here:
http://olive-drab.com/od_army-horses-mules_ww2.php
In Sicily and Italy, horses were used to overcome terrain that stymied mechanized units. On the drive to Palermo, 3d Inf. Div. captured hundreds of horses and mules. Gen. Truscott pressed them into service on his drive to Messina and they added enough value to be shipped to Italy when the fighting moved there. Truscott believed that more horses and mules in Sicily would have enabled him to capture more of the German force that ended up in Italy. Other commanders commented during the Italian campaign that horses would have helped and were superior to mechanized means in difficult, constricted terrain. However, when fighting bogged down at the Anzio beachhead, Truscott’s horse troop was disbanded.
After D-Day, horses to equip the 10th Mountain Division in Italy were procured from the mainland of France and mules for the same unit from the United States. They proved essential in the rugged Appenine mountains, north of Rome. From the beginning of the Sicily/Italy animal program until VE-day, approximately 15,000 animals were received and processed from local sources, Sardinia and Corsica, North Africa and the British Middle East. Quartermaster Remount Service in Italy issued 11,000 horses and mules to using forces. QM also had to supply food for the animals since local forage was insufficient.
When Allied forces captured the Po Valley in the north of Italy, tens of thousands of riding and draft horses were discovered running free, abandoned by the retreating Germans. They included some of the best German and Austrian stock, along with the best of the Italian breed, which had been procured as the Germans rolled back from Reggio and Salerno to the Po River.
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A peak in demand for military horses in the U.S. occurred in 1943. The Coast Guard asked for 3,000 horses to be used by its beach patrols
I believe mules were also used in Burma. They were well-suited to the terrain, if not the climate.