HIGH OR LOW PROTEIN?
When legislation obliged us to remove routine antibiotics from our feed formula, we saw the emergence of gut disorders partly coming from the fermentation in the animal intestine of the undigested fraction of protein. Nutritionists started then to adjust formulas to reduce the undigested portion of protein by incorporating highly digestible sources of proteins.
Some nutritionists still continue to formulate with level of crude protein higher than legal minimum required in order to seduce their customers. But it actually do not serve farm performance. If we want to improve feed performance, we must start to educate customers that crude protein is often an indicator of non-performance. They should actually look at the level of digestible protein. In the article below, I made few simulations of formulas to illustrate how protein digestibility evolves when we modify the level of crude protein in a least cost environment. Minimum level of crude protein imposed by local government
I built several scenarios on a piglet starter feed using a minimum level of 11g / kg of Digestible Lysin. I made 6 simulations; 2 simulations with a mini crude protein at 21% and 22%, 3 simulations with a maximum crude protein at 16.5%, 17% and 18% and one simulation without any constraint on the level of crude protein. The first conclusion is that the most economical level of crude protein for a 11g/kg of Dig Lysin would be 19.3% of CP (given the other nutrients selected for this simulation). But pushing the level of CP to 21% and 22%, we are actually increasing our cost respectively by 2.5% and 4.2%. Reducing the level of CP below 19.3% while maintaining 11 g/kg of Dig Lys will inflate as well the cost by 0.4%, 1.0% and 11.1% when setting maxi at respectively 18%, 17% and 16.5%. When we are pushing up the level of crude protein, the software will actually look for cheap non digestible protein to fill up the gap at the lowest cost. At the opposite, when we set maximum level of CP, we will favor highly digestible protein, namely synthetic amino-acids. In the table below, we follow the digestibility of lysin according to the level of CP.
The Dig Lys remains the same while the level of Total Lysin is increasing. The difference corresponds to the undigested portion of Lysin that is almost doubling from 0.82g/kg for a 16.5% CP diet up to 1.5g/kg for the 22% CP. That will affect negatively the Lysin digestibility that will jump from 7% up to 11.9%. The motivation to increase the level of CP of a diet is multiple but nutritionist must keep in mind that this is affecting negatively the cost and the performance of the diet. Naturally, we are observing similar trends for the other amino-acids as demonstrated in the table below.
Just by looking at the 8 amino-acids, the total quantity of indigestible fraction increase from 6.9g/kg up to 11.4g/kg. Ideally, we should look as well at all the other amino-acids. To do so, we can create a new nutrient in our formulation matrix to be called NDP for Non Digestible Protein. We can update our raw materials matrix with the NDP of each raw materials by looking at INRA or NRC references in order to calculate the average NDP of our diets. These simulations have been made on piglet feed but the similar rationale applies for any stage from sows to finisher and all stages for Poultry. These additional indigestible proteins that we provide through the diet will actually feed proteolytic bacteria in the colon of the animal to produce 5 different metabolites
Branched chain fatty acids
These metabolites can have some negative impact of the digestive physiology. An increase of production of ammonia could depress the production of mitochondrial ATP and reduce the expression of butyrate receptor. As result of lysin and arginine fermentation, we will produce respectively some cadaverine and putrescine which bring very strong smell to feces. The fermentation of tryptophan will produce some indole and skatole. The methionine and cysteine will be transformed into hydrogen sulfide which will trigger gut inflammation through the inhibition of
Cytochrome C (mitochondrial respiration)
Butyrate oxidation (energy deficit in colonocytes)
By monitoring the level of NDP in our diets, we will rapidly notice the close correlation of high level of NDP with diarrhea in piglets and MMA in sows and we can then start putting some maximum level of NDP in our formulation strategy to reduce bacterial proteolysis and all related disorders. Nevertheless, there are two dimensions that we need to take into account when we are forcing for lower CP content to improve protein digestibility. As result of this dynamics, we will reduce the content of soya bean meal and increase the contribution of synthetic amino-acids. For young piglets, we must avoid too much synthetic amino-acids but prefer highly digestible source of natural raw materials. To do so, we may want to set some maximum levels of synthetic amino-acids for the prestarter diet. For other stage, we do not need such constraint. The reduction of soya bean meal in your diet will bring as well a reduction of total dietary fiber. That needs to be compensated by the incorporation of other fibers to be sure that the NDF stays above the acceptable level. A too low NDF could trigger other physiological disorders. Among all fibers, it is critical to favor fermentable fibers in order to feed the cellulolytic flora. Indeed, the fermentation of proteolytic flora may create some unbalances that would affect the cellulolytic flora and it is important to support its development by providing the proper fermentable fibers. Soluble fibers would be fermented earlier in the intestine and will not feed the cellulolytic flora in the colon. You need to select a fiber that is both insoluble and fermentable in order to reach the colon population and help to balance the negative effect of the protein fermentation.