The Confederate army experienced a persistent shortage of horses and mules, and requisitioned them with dubious promissory notes given to local farmers and breeders. Union forces paid in real money and found ready sellers in the South. Both armies needed horses for cavalry and for artillery. Mules pulled the wagons. The supply was undermined by an unprecedented epidemic of glanders, a fatal disease that baffled veterinarians. After 1863 the invading Union forces had a policy of shooting all the local horses and mules that they did not need, in order to keep them out of Confederate hands. The Confederate armies and farmers experienced a growing shortage of horses and mules, which hurt the Southern economy and the war effort. The South lost half of its 2.5 million horses and mules; many farmers ended the war with none left. Army horses were used up by hard work, malnourishment, disease and battle wounds; they had a life expectancy of about seven months.