How much should a rat eat? - briefly
An adult laboratory rat normally eats 15–20 g of standard pelleted feed each day, about 5–7 % of its body weight. Juvenile rats need roughly 10 % of their body weight, divided into several small meals.
How much should a rat eat? - in detail
Rats require a diet that supplies sufficient energy, protein, fat, fiber, vitamins, and minerals to support growth, reproduction, and normal activity. Energy needs are commonly expressed as kilocalories per gram of body weight. An adult laboratory rat weighing approximately 250 g typically requires 13–15 kcal day⁻¹, which translates to roughly 3–4 g of a standard laboratory pellet per 100 g body weight. Pet rats of similar size consume about 20–25 g of a high‑quality commercial mix daily; adjustments are necessary for larger or smaller individuals.
Nutrient composition of an appropriate maintenance diet:
- Protein: 18–20 % of total calories, supplied by soy, casein, or animal‑derived sources.
- Fat: 4–6 % of total calories, primarily from vegetable oils.
- Fiber: 4–5 % of diet, essential for gastrointestinal motility.
- Moisture: 10–12 % of feed, aiding hydration and digestion.
- Vitamins and minerals: provided at levels meeting the National Research Council recommendations for rodents.
Feeding frequency influences intake regulation. Offering food ad libitum maintains steady consumption but may encourage obesity in sedentary rats. Controlled portions delivered twice daily reduce waste and allow monitoring of weight changes. Juvenile rats (3–5 weeks old) need 25–30 % more calories per gram of body weight than adults and benefit from a higher protein content (20–22 %). Pregnant or lactating females increase intake by 30–40 % and require additional calcium and phosphorus.
Overfeeding leads to excess adipose tissue, reduced fertility, and shortened lifespan. Underfeeding results in stunted growth, weakened immune response, and increased susceptibility to disease. Regular weighing (weekly for adults, bi‑weekly for juveniles) provides objective data for diet adjustment. A weight gain of 1–2 g per week indicates adequate nutrition for growing rats; stable weight within 5 % of target body mass reflects proper maintenance for adults.
Practical feeding guidelines:
- Measure dry feed with a calibrated scale; avoid estimating by volume.
- Provide fresh water at all times; rats typically drink 10–15 ml day⁻¹.
- Supplement with small quantities of fresh vegetables (e.g., carrots, broccoli) no more than 10 % of total intake to increase fiber and micronutrients.
- Exclude high‑fat treats, sugary foods, and raw seeds that may cause digestive upset.
- Replace uneaten food daily to prevent spoilage and bacterial growth.
Adhering to these quantitative parameters ensures that rats receive balanced nutrition, supporting optimal health and experimental reliability or pet well‑being.