Final answer:
The most likely use for cattle hair when the animals are processed is in the creation of leather products. Unused hair can also be utilized as fertilizer due to its high protein content.
Step-by-step explanation:
When cattle are processed, the animals' hair is most likely used for leather products. During this process, the hides of the cows are treated to create leather, which may retain some hair depending on the desired end product. However, the hair that is not used in leather can be utilized for other purposes such as fertilizer, due to its high protein content that can benefit soil quality. While cattle hair is not typically used for gum or upholstery directly, it might be indirectly involved in these industries through the use of processed leather.