NRC Model Issues Related to Mixes

First , let's establish that when working with separate ingredients there are no known issues. Formulate2 and the NRC model will balance down to the duodenal AA level quite nicely. Having said that, bear in mind that the NRC2001 model was conceived on the basis of providing detailed, specific calculation of energy and protein values for each individual class of feeds and within that domain, it excels.

However, when ingredients of different categories are combined as is common practice with pre-mixes and mixed feeds we enter a different arena. The methodology of the NRC model with respect to calculating digestibilities and energy values employs different equations for different classes of feeds. This methodology is implemented by differentiating classes of feeds with category assignments. The category assignment then determines which equations will be used to calculate digestibilities and energy.

Obviously, when different classes of feeds are combined as is most often the case with mixes, only one category may be assigned to the mix. This intrinsic limitation is problematic especially when working with mixes in tightly constrained diets.

Additional issues of scale appear to be involved with mixes that include rumen protected AA. These types of mixes are generally used in diets that are balanced at the duodenal AA level. It appears that at least one of the primary issues here is associated with accurate calculation of A, B and C protein fractions and the Kd value for the combined mix and how the mix with generalized values for these items is evaluated by the NRC equations as opposed to how the separates interact with those same equations.

Recap of Issues

Just to reiterate, the issues described above are only encountered when feeds of different classes are combined in a premix or mixed feed. Formulating diets down to the duodenal AA level with separate, individual ingredients works very smoothly and produces very accurate results both on paper and in the cow provided your inputs are accurate at all levels.

The difficulty arises when individual ingredients of a solved diet are combined in a mix. If the mix combines different classes of feeds, attempting to formulate the same diet by substituting the mix for its separates will not yield the same results. If the diet is tightly constrained, the effect of these limitations is exacerbated and a feasible solution may not be possible. Even if a solution can be obtained, it will not be reliable at the AA level.

While ultimately, because they are interconnected with the theoretical basis of the model, it may not be possible to resolve all of these issues directly, we are working to develop viable strategies that will simplify working with premixes and mixed feeds.

As these approaches are developed we'll post the details here.

(2007/10/24) Addendum to the 2007/07/31 Posting

At Central Valley Nutritional Associates we've adopted the practice of selecting pre-mix items from the diet for the highest producing animals. Once the items have been selected, their composition is saved to the mix clipboard and their analysis is saved to the feed clipboard. The high producing ration record is then cloned and the solution amounts displayed in the feeds minimum column using the Diet Detail form.

Once this step has been completed, the premix feed is added to the feeds grid and it's inclusion rate is entered in the feeds minimum column. The minimum column values of the separate items of which the premix is composed are then deleted. Load sheets for the high producing diet can then be generated using this cloned record. The original record with indvidual ingredient items provides an accurate detailed analyisis of the diet.

In diets of lower producing animals, the premix may be offered for inclusion in the diet during the optimization. The resulting diet solutions may then be detailed and proofed by cloning the solved diet record and using the Diet Detail form and the Formulate menu Calculate option. In this case, the cloned detailed record provides an accurate detailed analysis of the diet

This is a very workable method that allows full optimization with the premix in diets of lower producing animals and eliminates the need to formulate above the actual production targets since this step is primarily used to produce a premix that will solve in the high producer diet. Solving with the premix in the high diet is not necessary if the method described above is employed since load sheets may be generated without doing so.

Just remember, as explained both above and below, AA constraints cannot be successfully enforced when working with mixes if the primary AA sources are combined in the premix. It is doubful that feasible solutions could be found even if they are not included in the premix because of the issues outlined on this page. That of course doesn't mean that you can't formulate accurately for AA using a premix - you can if you follow the basic guidelines posted here.

Also, the inclusion of fats or fatty-acids in a premix creates the greatest distortion in its calculated energy value since the equations used for digestibility and energy for these items is significantly different from all other classes of feeds (see 2007/07/31 posting).

(2007/07/ 31) - Workaround for formulating with premixes and mixed feeds

The methods below will allow you to successfully and accurately work with mixes within the NRC 2001 model. The process below was devised with a diet that included Calcium Salts as a source of fatty acids at the rate of approximately .5 lbs hd/day. The issues described above that pertain to energy equation class assignment and combining feeds of different classes in a premix are especially evident when combining fats or fatty acids with other feeds since the equations used for these items are very different from those used for feeds classified as an energy or protein source. The net result is that the contribution of these items to the energy value of the premix is significantly understated when the Energy Source category is assigned to the premix. The steps outlined below are designed to work around this fact so that the premix will produce a feasible solution when substituted for its separates. It is probable that as the inclusion rate of fats or fatty acids increases above that of the diet used to develop the guidelines, it will be necessary to increase the margins above the NE(l) and MP allowable milk targets as described in items 6 and 7 below.

If fats or fatty acids are not included in a diet, it may be possible to work with the NE(l) and MP allowable milk targets without making any adjustments. However, the greater the inclusion rate of these items in the premix the greater wil probably be the need for adjusting the targets. Digistibility and energy equations for these items are significantly different from all other classes of feeds.

If you wish to work directly with predicted or stipulated DMI, follow the procedure listed below.

1. Select the premix items from the separates diet for high producing animals after completing the appropriate sets below
2. Set the target production level
3. Do not set a Prop DMI constraint
4. Bind MP
5. Optimize the diet to get an initial feasibility
6. Using the NE(l) and MP allowable milk report and a little trial and error, manually adjust the MP requirement until MP milk is optimizing about .5 lbs over the target
7. Work with NE(l) allowable milk moving the minimum NE(l) constraint up until it is supporting about .75 to 1.0 lbs over the production target
8. When you’ve met these benchmarks, make your premix from the separates and create a feed record using the feed clipboard. Regardless of its composition, assign the premix to the Energy Source category.
9. Clone the ration record you worked with to create the separates solution and use it to optimize the diet with the premix.
10. Substitute the premix for the separates
11. Make sure your user entered MP constraint is present and bound and that the NE(l) constraint is returned to its original value. Re-setting the NE(l) constraint may or may not be necessary.
12. If you’ve optimized for AA – UNBIND the AA constraints
13. If mineral is included in the premix, make sure that a nutrient constraint is set for an item that can only be met by the premix such as Iodine. This will insure that the premix is pulled into the diet at the correct amount. If mineral isn’t in the premix set another nutrient constraint that will have the same effect.

Pushing energy and MP supplies slightly over their requirements does two things.

• It helps to compensate for the lower energy value that results from combining feeds in a mix where only one category assignment can be made.
• And it helps to compensate for inherent inaccuracies in calculating A, B and C fractions and Kd values for combined feeds. This allows the optimizer to balance at the MP level with a mix already formulated for appropriate duodenal AA supplementation without the need to enforce AA constraints which would cause infeasibilities because of these inaccuracies.

It may be necessary to massage the RDP or other constraints of the premix solution a little to get exactly what you want. However, after optimizing with the premix, if you now go back and detail the premix diet solution by breaking out the separates from the premix and then do an evaluation using the Calculate menu option in the Formulate menu, you will find that everything is where it is supposed to be – including AA concentrations and ratios.

If you are working with a diet that is scaled to a DMI value below the predicted or stipulated DMI but you are still formulating for the original production targets, the following approach may be useful.

1. Select the premix items from the separates diet for high producing animals after completing the appropriate sets below
2. Set the target production level
3. Set Prop DMI to the desired value
4. Bind MP
5. Optimize the diet to get an initial feasibility
6. Using the NE(l) and MP Allowable milk report and a little trial and error, manually adjust the MP requirement until MP milk is optimizing about .5 lbs over the target
7. Make sure that energy allowable milk is very near the production target - slightly over or slightly under will probably work but you may have to do a little "trial and error" to find a workable value.
8. When you’ve met these benchmarks, make your premix from the separates and create a feed record using the feed clipboard. Regardless of its composition, assign the premix to the Energy Source category.
9. Clone the ration record you worked with to create the separates solution and use it to optimize the diet with the premix.
10. Substitute the premix for the separates
11. Make sure your user entered MP constraint is present and bound and that if the NE(l) constraint was adjusted, it is returned to its original value. Re-setting the NE(l) constraint may or may not be necessary.
12. If you’ve optimized for AA – UNBIND the AA constraints
13. If mineral is included in the premix, make sure that a nutrient constraint is set for an item that can only be met by the premix such as Iodine. This will insure that the premix is pulled into the diet at the correct amount. If mineral isn’t in the premix set another nutrient constraint that will have the same effect.

What these approaches do is build a fudge factor into the energy and protein densities of the premix. The fudge factor then compensates for the effect of combining items in a premix and allows the optimization engine to formulate successfully with the premix. As you use the premix in diets with lower levels of production the fudge factor becomes increasingly irrelevant.

For instructions on how to quickly and easily detail the diet with the premix components, download and install the most recent Formulate2 maintenance update and click on the Detail Diet option of the ration record Other menu. This will display the Diet Detail form shown below.

For instructions on how to detail a diet using this form, click on the form Help button.

Online Tutorial (requires active internet access)

• Optimizing with Mixes - How to create pre-mixes that will optimize accurately when substituted for the separates of which they're composed. (voice-over narration: 7.54 MB EXE)
• Working with Pre-mixes - How to create pre-mix feed records from a complete diet formulation. (voice-over narration: 4.29 MB EXE)

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