Step 1: Recall what raw material furfural needs.
Furfural is manufactured by acid hydrolysis and dehydration of pentosan sugars, which are a component of hemicellulose, so any agricultural residue that is rich in pentosan-containing hemicellulose is a candidate raw material.
Step 2: Screen the given options for pentosan content.
Cattle waste and cow dung are largely digested organic manure material used mainly for composting or biogas generation and carry very little usable pentosan for chemical extraction. Sewage similarly has negligible pentosan content and is not processed for industrial chemicals.
Step 3: Identify the correct by-product.
Bagasse, the fibrous sugarcane residue left after juice extraction, is well known to be rich in pentosan hemicellulose and is one of the standard commercial feedstocks used worldwide to manufacture furfural.
\[ \boxed{Bagasse} \]