Sterilized surgical Catgut ( Relyon Gut) consists of a strand prepared from collagen derived from healthy mammals purified and sterilized. The most widely used source is the submucosa of the small intestine from sheep or lambs and to a lesser extent, the serosa sheep beef cattle.
The length of ovine intestine is about 20 m and it is desirable in the preparation of surgical Catgut ( Relyon Gut) that the diameter of the intestine should not be more than 18 mm. A number of factors are important in the selection of suitable intestinal material. Obviously intestines will vary considerably depending on the age of the animal, the pasture, climate, etc. and it is not uncommon to find that intestines from some animals have been affected by scar tissue and are not suitable for preparing surgical Catgut ( Relyon Gut). Generally speaking the younger the animal the smaller it‟s intestine, and less likely to be affected by feed.
A number of manufacturers of Catgut ( Relyon Gut) use only the first 8 m of intestine measured from the duodenum. In the meat trade such intestine are described as ligature casing or runners. In the slaughterhouse the gut is removed from the animal by the gut pullers and is first of all cleaned to remove faecal matter after which it is inspected, measured and the preserved either in a frozen state or salted. The largest suppliers of intestines come from Australia and New Zealand and the slaughterhouses in these countries are well equipped to deal with the vast number of animals involved. The intestine of any cadaver is the most vulnerable to bacterial attack and decomposition of this part of the body always begins earlier then any other. It is, therefore, vitally important that the slaughterhouse technique involves rapid cleaning and freezing or preservation by other methods in order to keep the bacterial growth as low as possible.
The ovine intestine consists of four layers (see figure). The outermost is known as tunica serosa or serous layer, much of which is torn off in removal from the animal; next the tunica musculosa made up of two layers, one longitudinal and the other circular; the third layer is the tunica submucosa from which Catgut ( Relyon Gut) is prepared and in the innermost layer is the tunica mucosa or mucous coat which is the wall to the lumen of the intestine. The intestine receives its blood supply from the mesenteric artery and being some twenty eight times the length of the sheep itself is twisted into a mass of convolutions until near its end where it ascends to join the colon. The Medical Research council report on the preparation of Catgut ( Relyon Gut) contains interesting microphotographs of the submucosal layer. The manufacturer of surgical Catgut ( Relyon Gut) receives intestines either intact or rough scraped at the abbatoir. Made up as knots or bundles which may be frozen, salted or in brine, and the first step is to soak these in water to thaw out or to remove salt and 0prepare them for splitting. It may be noted in passing that the intestines destined for sausage skins are not split but are cleaned and scraped in the tubular form and known as sausage casings. This cleaning usually takes place in the abbatoir and the product is marketed in barrels or casts.
Splitting Inserting the curved horn of a cutting tool into the end of the intestine and pulling the runner over cutting blades carry out the splitting or cutting operation. The number of ribbons produced can be varied but is usually two or three. The horn follows the curvature of the intestine and therefore can be said to locate down the track of the mesenteric vein, which is often called the rough side as distinct from the upper part known as the smooth side. The two parts of the intestine are kept separate throughout the process as they behave in different ways physically and chemically.