Agricultural Science (AS)·Animal science · NSSCAS 4.2b
Feed analysis: dry matter, ash & digestibility calculations
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A farmer near Otjiwarongo is about to buy two bales of hay for his cattle. They look the same, but one is heavy with water and the other is dry, leafy and rich. How much of each bale is real food, how much is just water, and how much can the animal actually digest? In this lesson we turn a lump of feed into numbers a farmer can trust, working out moisture, dry matter, ash and digestibility step by step.
What you'll learn in this lesson
By the end you should be able to (NSSCAS Agricultural Science (AS) 4.2b):
- Recall what moisture, dry matter, ash and digestibility mean in a feed
- Describe the laboratory methods used: oven-drying for moisture and dry matter, and a muffle furnace for ash
- Calculate the moisture content of a feed using moisture % = (water lost on drying / fresh mass) x 100
- Calculate the dry matter content using dry matter % = (dry mass / fresh mass) x 100, and check it as 100 - moisture %
- Calculate the ash content using ash % = (mass of ash after burning / mass of sample) x 100
- Calculate nutrient digestibility using digestibility % = (nutrient intake - nutrient in faeces) / nutrient intake x 100
- Lay out calculation working clearly: formula, then substitution, then answer with units
- Apply these calculations to feed testing and ration formulation on a Namibian farm
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Miss Elina and Mike talk through the whole topic — with the figure and working drawn live.