Ruminants do not normally show deficiency symptoms of vitamin B complex because

Ruminants do not normally show deficiency symptoms of vitamin B complex because the bacteria present in their rumen synthesize the vitamins. These bacteria are able to produce the vitamin B complex in adequate amounts, which is then absorbed by the ruminant's body. This process is made possible due to the unique four-chambered stomach of the ruminants, which allows for the fermentation of plant materials by the bacteria in the rumen. As a result, ruminants are able to derive their vitamin B complex requirements from the microbial synthesis in their rumen, and do not rely on dietary sources for these vitamins.