The B vitamin complex (B1, B2, B3, B5, B6, B12, folate, biotin) supports energy metabolism, nerve function, red blood cell production, and overall vitality. Guinea pigs produce some B vitamins through cecal fermentation and reabsorb them by eating cecotropes (a normal, essential behavior — do not prevent it).
Met through a combination of hay, pellets, vegetables, and cecotrope consumption.
Lethargy, poor appetite, weight loss, neurological symptoms (head tilt, unsteady gait).
Water-soluble vitamins, so excess is excreted. Toxicity is virtually unknown.
Dietary fiber from hay fuels cecal bacteria that synthesize several B vitamins — including B12, biotin, thiamine, and folate. Without adequate fiber, the cecal microbiome collapses, and with it the guinea pig's primary internal source of these vitamins. This makes fiber not just a macronutrient but the engine that drives B vitamin production.
What this means: Unlimited timothy hay is non-negotiable. When hay intake drops — due to dental problems, illness, or a guinea pig being selective about food — B vitamin status can deteriorate within days. If a guinea pig stops eating hay, treat it as an emergency.
