01-20-2015, 08:44 PM
Dry matter means the quantity of feed when all the water have been driven off. Fresh grass contains about 25% dry matter (DM). This means that a 100kg of such grass will contain 25kg solid and 75kg water. So if you have a 20kg goat that needs a daily feed intake of 4% of its body weight in DM, you'll need to feed it ...... Kg of grass per day?
Let's calm down a bit. Goats don't need only grass to meet their nutrient requirement. They need concentrates too. So let's say you're feeding them 80% grass and 20% concentrate.
So the total DM requirement of the goat is 4/100 x 20kg = 0.8kg DM. Now 80% of this value should be grass and 20% concentrate. So:
80/100 x 0.8kg = 0.64kg grass DM.
Concentrate needed is then 0.8kg-0.64kg = 0.16kg concentrate DM.
Let's focus on our grass:
we know that our fresh grass contains only 25%DM and we need enough fresh grass to supply 0.64kg DM. Here is how you do the calculation:
100kg fresh grass contains 25kg DM
How many kg of fresh grass will contain 0.64kg DM? It will be less, so more should divide:
0.64/25 x 100 = 2.56kg of fresh grass is needed.
Remember that we need 0.16kg DM of concentrate feed. It is important to know the DM content of your concentrate. Let's assume 90%. So:
100kg concentrate contains 90kg solid.
How many kg of concentrate will contain 0.16kg DM? It will be less, so more will divide.
0.16/90 x 100 = 0.21kg concentrate.
Finally, our 20kg goat needs 2.56kg of fresh grass and 0.21kg of concentrate every day.
Let's calm down a bit. Goats don't need only grass to meet their nutrient requirement. They need concentrates too. So let's say you're feeding them 80% grass and 20% concentrate.
So the total DM requirement of the goat is 4/100 x 20kg = 0.8kg DM. Now 80% of this value should be grass and 20% concentrate. So:
80/100 x 0.8kg = 0.64kg grass DM.
Concentrate needed is then 0.8kg-0.64kg = 0.16kg concentrate DM.
Let's focus on our grass:
we know that our fresh grass contains only 25%DM and we need enough fresh grass to supply 0.64kg DM. Here is how you do the calculation:
100kg fresh grass contains 25kg DM
How many kg of fresh grass will contain 0.64kg DM? It will be less, so more should divide:
0.64/25 x 100 = 2.56kg of fresh grass is needed.
Remember that we need 0.16kg DM of concentrate feed. It is important to know the DM content of your concentrate. Let's assume 90%. So:
100kg concentrate contains 90kg solid.
How many kg of concentrate will contain 0.16kg DM? It will be less, so more will divide.
0.16/90 x 100 = 0.21kg concentrate.
Finally, our 20kg goat needs 2.56kg of fresh grass and 0.21kg of concentrate every day.