Which carbohydrate type is less digestible due to its composition in mature plants?

The correct answer is based on the understanding of plant carbohydrate composition, particularly as plants mature. Lignin is a complex polymer found in the cell walls of mature plants, functioning primarily to provide structural support and rigidity. As plants mature, the cellulose and hemicellulose content often increases, and lignin levels elevate as well, making the plant material tougher and less palatable.

This increased lignin content directly contributes to decreased digestibility. Unlike simple carbohydrates such as sugars and pectins, which can be easily broken down by the digestive systems of herbivores, lignin is resistant to microbial breakdown in the rumen. Consequently, for dairy cattle and other ruminants, feeds high in lignin yield less energy from carbohydrates since they cannot access the energy stored in these components effectively.

Fructans, while also carbohydrates, are more digestible because they are composed of fructose units that can be fermented by rumen microbes. Sugars are highly digestible and provide quick energy, while pectins can be fermented but are not as robustly resistant as lignin. Therefore, lignin stands out as the carbohydrate type that significantly reduces digestibility in mature plants due to its unique chemical structure and role in plant physiology.