Why can't rats have milk? - briefly
Rats lack sufficient lactase, the enzyme needed to break down lactose, so consuming milk causes gastrointestinal distress. Consequently, milk is unsuitable as a regular food source for them.
Why can't rats have milk? - in detail
Rats lack the enzyme lactase in sufficient quantities after weaning, so they cannot break down lactose, the sugar present in most mammalian milk. Undigested lactose remains in the gastrointestinal tract, where it draws water osmotically and is fermented by intestinal bacteria. This leads to rapid onset of diarrhea, abdominal cramping, and dehydration, which can be fatal in small animals.
In addition to lactose intolerance, milk proteins such as casein can provoke immune reactions. Rats may develop hypersensitivity to these proteins, resulting in intestinal inflammation and systemic allergic responses. The combination of osmotic diarrhea and potential allergic colitis compromises nutrient absorption and overall health.
Key physiological factors:
- Lactase deficiency – low enzymatic activity after the neonatal stage.
- Osmotic load – excess lactose increases intestinal water content.
- Bacterial fermentation – produces gas and short‑chain fatty acids, irritating the gut lining.
- Protein sensitivity – possible immune-mediated inflammation from casein.
Because of these mechanisms, providing milk to adult rats poses a serious health risk. Safe hydration for rodents should rely on water and, when necessary, specially formulated rodent diets that exclude lactose and dairy proteins.