The phrase "natural gut" refers to the material used to make strings for sports equipment like tennis rackets. It means that the strings are made from natural materials, specifically the intestines of cows. Full definition
Natural gut bacteria plays a vital role in building and sustaining a strong immune system. (kaboutjie.com)
Cobalt Aquatics CA Mysis Suitable for freshwater and marine fish, Cobalt Aquatics» highly nutritious frozen CA Mysis shrimp are live - caught with natural gut loads of phytoplankton and other amino acids. (petbusiness.com)
It is stuffed in natural gut casing and allowed to air - dry for 2 weeks. (jovinacooksitalian.com)