Natural guts used in tennis racquets are made from a part of the cow’s intestine called the serosa. A cow’s serosa has high tensile strength and is long which makes it ideal for tennis strings.

How many cows does it take to produce a tennis string? On average, it takes about three cows to produce a tennis string. That’s because the serosa is a small part of the intestine. Though the cow’s intestine is 120 feet long, serosa is found on only the stretchy outermost layer.

The quality of the serosa varies from freed to breed and from region to region. Cows from the Taranaki  region in New Zealand have produced strong guts and is widely used.

Many tennis players prefer natural guts because of their ability to retain tension and high elasticity. But natural guts can be expensive and break more easily compared to synthetic strings.