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Newsletter Nutrispices

September 2016 - Issue 22
 

THE HIGHEST FEED COST MAY NOT BE WHAT YOU THINK

Dear <<First Name>>,

Many feedstuffs that are commonly used in preparing diets for animals contain antinutritional factors (ANFs). These factors interfere with the utilization of dietary nutrients in a variety of ways, including reducing protein digestibility, binding to various nutrients or damaging the gut wall and thereby reducing digestive efficiency.

The main ANFs that interfere with nutrient digestion and absorption are lectins, protease inhibitors, tannins, antigenic proteins, phytic acid, glucosinolates and gossypol. The application of heat substantially reduces the activity of several ANFs, and in particular lectins and protease inhibitors. An effective means to improve the availability of phosphorus bound to phytic acid is the use of exogenous phytases. For tannins and glucosinolates, no practical means for inactivation are yet available. More information is needed before we can routinely quantify levels of ANFs in feedstuffs and relate ANF contents to effects on true nutrient digestibilities and gut endogenous nutrient losses.
 
 
Arabinoxylans Beta-glucans
Glucosinolates Gossypol
Lectins Phytate
Protease inhibitors Zinc Oxide
Tannins  
 
Arabinoxylan is a hemicellulose found in both the primary and secondary cell walls of plants, including cereal grains. The water-soluble arabinoxylans change the viscosity of the intestinal contents, resulting in reduced nutrient digestibility and absorption. Commercial enzymes are available that can be added to poultry feed to counter the negative effects of arabinoxylans.
 
Beta-glucans bind with water in the intestines, resulting in the formation of gels that increase the viscosity of the intestinal contents. The increase in viscosity of the digesta associated with increased gel formation adversely affects digestion and absorption of nutrients. There are, however, several enzymes (ß-glucanases) that can be added to feed to decrease intestinal viscosity and thereby increase nutrient availability.
 
Glucosinolates are present in all cruciferous seeds and plants, in particular rapeseeds. This ANF is at the origin of kidney and liver lesions in pigs and poultry. The effects of glucosinolates can be overcome by the use of supplemental copper sulphate or iodine in the diet. However, the most promising means to reduce effects of glucosinolates is reducing their content in feedstuffs through plant breeding. Consequently, the use of rapeseed or rapeseed meal in diets for young animals should be avoided and there is need for the development of plant varieties with even lower levels of glucosinolates.
 
Free form Gossypol is a toxic compound found in the cotton plant in high concentration Gossypol can cause extensive egg yolk discoloration and yolk mottling.
 
Lectins are proteins that have the unique property of binding carbohydrate-containing molecules, which cause the agglutination of red blood cells. In the digestive tract, agglutination causes the atrophy of the microvilli, reduces the viability of the epithelial cells, and increases the weight of the small intestine caused by hyperplasia of crypt cells. Moist heat treatment will destroy much of the lectin present in grain legumes. Lectins, however, are quite resistant to inactivation by dry heat treatment.
 
Phytate is the principal storage form of phosphorus in many plant tissues, especially bran and seeds. Phytate has been shown to block the absorption of not only phosphorus but also other minerals, particularly calcium, magnesium, iron, and zinc. Phytate has also been shown to negatively affect the absorption of lipids and proteins. At least 75% of the total phosphorus in corn, for example, is in the form of phytate-phosphorus.
Phytase is now available as an additive to animal feeds to help with the breakdown of phytate. Breeders are also looking to produce low-phytate grains and legumes.
 
Protease inhibitors are small protein molecules that have the ability to interfere with the action of the proteolytic enzymes. Trypsin inhibitors have been isolated from many legumes, including soybeans and field peas.
Proper heat treatment in combination with the correct moisture level destroys the trypsin inhibitors. For soybean meal this is accomplished in the desolventising / toasting chamber. In the case of full fat soybean meal, the most common method is extrusion. Insufficient heating, or under-processing, of soybean meal negatively affects amino acid digestibility because the anti-nutritional factors are not adequately destroyed. Excessive heating, or over-processing negatively affects amino acid digestibility because a portion of the amino acids have either been destroyed or tied up as indigestible, bound compounds.
 
Tannins are responsible for the astringent taste of some leaves, fruits, and wines. Tannins are found in plant leaves, bark, fruit, wood, and roots. They have been closely linked with plant defense mechanisms against ruminant animals, birds, and insects. Tannins have the ability to bind protein, making them unavailable to the animal. But at low dosage, tannins can actually have a positive impact on animal growth.
 
Zinc Oxide is normally not considered as antinutritional factor. It is a common source of zinc in Swine and Poultry. But recent studies underlined that, when it is used at high dosage (3000ppm) to prevent diarrheas in piglets,  it interacts negatively with phytase, copper, iron and acids in the gut.
 
Zinc Oxide binds to the phytate complex and prevent the attacks of the phytase enzyme and therefore the availability of phosphorous. Studies shows that the use of high level of Zinc Oxide in piglet feed requires an increase of available phosphorous to avoid deficiencies.
 
High level of Zinc Oxide will negatively impact the absorption of copper and iron. Zinc, copper and iron are using the same pump to enter enterocytes. In case of excess of Zinc, the chances of iron and copper to enter enterocytes will decrease. When using high dosage of Zinc Oxide, it is required as well to overdose copper and iron to maintain animal growth.
 
Zinc Oxide, like carbonate calcium is known as well to bind acids. The use of high level of zinc oxide will negatively impact the acidification of the stomach and increase its pH by 0.5 unit. Nutritionist usually add some acidifiers to the formula to help the stomach acidification but high level of Zinc Oxide will neutralize them as well preventing them to be effective.
 
In summary, the use of high dosage of Zinc Oxide will cost more than it appears. Instead of the 6 USD per ton (2 usd / kilo at 3kg / ton of feed), the actual cost double to reach more than 13 USD per ton of feed.
Cheaper alternative solutions exist with similar effect on the prevention of diarrhea with significant potential savings.

Approximate prices and ingredients used for the calculation:
 Zinc Oxide: 2 USD / kg
Phytase: 10000 FTU/G: 13 USD/kg
CuSO4 (25% Cu): 2USD/kg
FeSO4.7H2O (20% Fe): 0,2USD/kg
CaCO3 (40% Ca): 0,07USD/kg
Lactic acid (80%): 1 USD/kg

 
Similar approach is possible for the other antinutritional factors. It would enable us to optimize the utilization of ingredients. We can not totally avoid antinutritional factors but we need to minimize their impact by taking both the primary and secondary cost of each ingredient into account.

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