Studies on Foreign-Body Bovine Ruminitis Caused by Ingestion of Polypropylene strings for Binding Rice Straws

The present study was carried out to clarify the actual condition of farms involv- ing in animal husbandry. The development of new type of farming machines has given rise to occur chronic digestive diseases of such a type as hitherto unexperienced in cattle, thus a lot of damages are being done to those farms. The use of a newly-developed ”reaper-and-binder” has spreaded rapidly among farms since about 1969. It is capable of preparing handles of rice stems immediately after reaping. Polypropylene (PP) strings are used widely for their binding because extreme waterproof, and lightness. On the other hand, in Japan, many dairy and beef cattle feed on rice straws as roughage. PP strings are apt to be mixed with these straws being cut, so that it is not seldom for cattle to ingest PP string pieces with them. The ingested PP string is decomposed into fine longitudinal fibers in the rumen owing to the gastric movement. These fibers become entangled with one another, developing gradually into an irregular large foreign body, which turns into hard cal- culi composed mainly of calcium and phosphate. The present study revealed that a stone weighing 1.5―2. Okg was formed during 1 or 2years by continuous ingestion of PP string pieces. Intraruminal calculi thus formed by ingestion of PP string reached a maximum of 10―20kg in some cases. The present study revealed that the mucous membrane of the rumen containing these calculi was disturbed with sloughing off of mucosal papillae, degenerative thickening of the epithelium, and formation of small ulcers, pathological changes in foreign body ruminitis, leading to decreased digestive function. On an adult cow with a ruminal fistula experimentally made in the abdominal wall, a experiment was performed as follows: Thorough this fistula the cow was in- troduced 1,000―4,000 PP string pieces and foreign body masses extracted from field cows died of illness. Then, a rubber balloon was inserted into the rumen to examine gastric movement and properties of the gastric juice. As a result the gastric movement was accentuated in the presence of up to 2, 000 PP string pieces in the rumen,becoming apparently disturbed with an increase in the number of string pieces present in the organ. Concurrently, the changes in the properties of gastric juice were indicative of a digestive disturbance. Thus, the mechanism of onset of these disturbances was approximately clear. An integrated diagnostic method was established as the result of studies on the utilization of gastrofiberscope as well as the extraction of foreign body through an abdominal small hole. Surgical removal of foseign body mass by rumenotomy was found to be the only methos of treatment, and the function of rumenal mucous membrane disturbed by the presence of foreign body proved to be gradually restored even after operation. From the prophylactic viewpoint, experiments both in vitro and in vivo were carried out to see if it is possible to prevent this kind of disturbance by replacing the PP strings with those made of any other material than PP. It was found that hte rayon string (made from staple fibers) was digested in the rumen within 5 days of its application. Thus, it was confirmed that this rayon string, when used, led to the complete prevention of this kind of disease.