The only BW program during WWI was carried out by Germany.[1] Logistic systems during WWI depended on draft animals, primarily horses and mules. German agents used two pathogens, anthrax and glanders, in the countries and ports from which horses were being shipped to the allies in an effort to decimate the availability of the animals. Some mortality of animals being shipped did result, but the numbers were very small, and the effort had no military consequences whatsoever.
[1] Mark Wheelis, “Biological Sabotage in World War I,” in Erhard Geissler and John Ellis van Courtland Moon, eds., Biological and Toxin Weapons: Research, Development, and Use from the Middle Ages to 1945, SIPRI Chemical and Biological Warfare Studies, no. 18, Oxford, UK: Oxford University Press, 1999, pp. 35-62.