Optimising amino acid contents in each feed
The optimum economic amino acid content of the feed in each phase of a given feeding programme will decrease as the birds age, and this optimum will be dependent on the dietary energy content used in each phase. The optimiser determines the relationship between the amino acids and energy within each specified feeding period that will maximise or minimise the objective function. The objective is not to determine independently the optimum ratio in each of the feeds on offer, but to determine the optimum amino acid to energy ratio in each of the feeds in the feeding programme such that the overall performance is maximised. Because the performance on one feed impacts on the performance on subsequent feeds, this is an essential prerequisite in optimising the feeding of broilers.
To optimise amino acid contents the process works only with lysine. The contents of the other essential amino acids are controlled by reference to an (user-controlled) ‘ideal’ protein ratio. In the present version of the program both amino acid and energy contents are optimised simultaneously, although the user may fix either of these, thereby increasing flexibility.
To use this tool, select your optimiser flock, and go to the Amino acids tab.
You will see an extra set of columns in the feeding schedule under an AMEn header, and another under Lysine. These are used to define the AMEn and lysine values that the optimiser should consider for each feed. There are two basic methods that can be used to arrive at a solution.
- Numerical method
- Grid method
If the grid method is used, the user enters the number of points to be considered for each feed. The interval size is calculated automatically using the Min/Max bounds given for each feed, and the number of points to be considered. In this way the user retains control over the accuracy obtained for each value in a solution.
Note that if there are many feeds, then a large number of points can result in a very slow solution, as each combination of values has to be solved. It is therefore better to start with a low number of points, and to use the information from such a solution to narrow the ranges and increase the accuracy for a subsequent solution. This is particularly relevant for this tool, as there are two variables per feed, so solution time increases exponentially with each feed.
The points that will be considered are listed on the Points tab.
This table shows the Lysine and AMEn values that will be considered for each feed. The optimiser will consider all possible combinations of these points.
If the Refine soln. option is ticked, then the optimiser will do a final numerical solution using the best solution from the grid method as a starting point. This process is sometimes able to obtain a better solution than the grid method on its own.
If the numerical method is selected, then NAG (Numerical Algorithms Group) utilities will be used to solve the problem numerically. In this case, the columns that appear will be the Min and Max bounds (restricting the range of AMEn values that should be considered) as well as a Start AMEn column. This defines a starting point for the numerical method.
Note that this method is very sensitive to the starting point, and will not be able to find a solution if the starting point is not suitable.
An extra feature specific to this tool is the ability to specify the desired amino acid ratio that should be used in the feed. To keep the amino acid ratios as they were set up in the original feed, select <use feed ratios> from the list. Other ratios, such as Degussa, may be set up under the Options–Edit Ideal protein ratios menu item. Different ratios may be defined at different ages.
As the lysine value is changed in each feed during the optimisation process, the lower bounds of the other amino acids are adjusted according to the chosen ratios.
Once all inputs have been set up, click the Solve button on the bottom toolbar. Note that this button is only enabled if one input item of each type has been dragged down to the flock.