Animal Nutrition and Feeding
The six nutrient classes
Water, carbohydrates, fats, proteins, minerals and vitamins. For each, know the general function, one deficiency sign and two common feed sources. Protein is described by crude protein (nitrogen × 6.25); energy by metabolisable energy (ME); fibre by neutral detergent fibre (NDF) or acid detergent fibre (ADF).
Feed classification
- Roughages: high fibre, low energy - pasture, hay, silage, crop residues.
- Concentrates: low fibre, high energy or protein - maize, sorghum, oilseed cakes, molasses.
- Supplements: minerals, vitamins, salt licks, urea (non-protein nitrogen for ruminants only).
Feeding principles
Ration formulation balances energy, protein, minerals and vitamins against the animal's requirement for maintenance plus production (growth, milk, pregnancy, work). Dry matter intake rises with body weight and falls with increasing fibre content and heat stress. Water is the most limiting nutrient in practice; a lactating cow may drink over 100 litres a day.
Traps to watch
- Urea is toxic to monogastrics and must be introduced gradually with readily available carbohydrate.
- A high-protein diet is not automatically better; excess protein is wasteful, costly and burdens the kidneys.
- Silage and hay are roughages, but maize grain is a concentrate - do not classify by plant species.
- Mineral deficiencies are region-specific; copper, selenium, cobalt and phosphorus are the usual suspects.
Worked rule of thumb
To estimate daily dry matter intake for a growing ruminant, use roughly 2.5–3% of body weight. A 200 kg heifer therefore needs about 5–6 kg dry matter per day, split into roughage and concentrate according to growth target.
Practical advice
Change diets over 7–10 days, feed at consistent times, and always supply clean water and a mineral source. Record feed offered and refused so wastage is visible.