Problem

I would like help in the following manner. Based on parameters linked to the animal (like live weight, milk yield, fat% and protein % in the milk,..) I want to calculate the total nutrient requirement (DMI, energy, protein,...). Next I start putting together a ration that meets these requirements.

However, when I look in your book, and especially in the numerous examples, calculating the nutrient requirement starts from a certain ration. In nearly every exercise the q-factor is calculated first or given. This q-factor (quality) is related to the ration. But I want to calculate the requirements before I make a ration.

How can I do that and more important, what equations are you using to calculate the nutrient equations (DMI, ME, protein,...)

Response

Yes - you are right you need to know q before you calculate a ration!

Rumnut gets round this by calculating the initial requirements assuming a q=0.65. When you specify a ration, and whenever you change it, Rumnut recalculates all the requirements. Try adding 3 kg straw to a ration and look at the change in the requirements.

When you add an ingredient to the ration (say 2kg wheat) not only do you alter the q of the ration but you also alter the FME/EDRP balance and hence the rumen MCP output and the amount of DUP required. You may also alter the amount of Ca and P required in the ration.

When feeding an ingredient ad lib Rumnut actually iterates to a solution and works to 0.1% accuracy but on modern computers this happens so fast it is rarely seen.

The principle equations for predicted DMI and ME are from AFRC as outlined in the book; the MP requirements are as per AFRC but modified to reflect on-farm findings.

If none of these ways work you may need to contact me further assistance by email.