Because wet litter impacts broiler welfare and performance it is of vital importance to poultry producers. Wet litter in poultry houses may be caused by a number of factors including mycotoxins, disease, gut health, nutrition, management, housing and environment. Nutrition, including reducing mycotoxin contamination of feed, plays an important part in controlling litter moisture. The role of nutrition in maintaining dry litter has been reviewed on a number of occasions (Francesh and Brufau, 2004; Collett, 2012). This presentation examines some useful nutritional strategies for maintaining dry litter in broiler houses.
Nutritonal Factors Impacting Litter Moisture.
It has been well established over many years that non-starch polysaccharides (NSP) such as arabinoxylans and beta-glucans from cereals and oligosaccharides from legumes and protein meals are poorly digested by chickens. Cereals have different levels of NSP ranging from very high (rye) to very low (rice) and the content of NSP is inversely proportional to the rate of energy metabolisability (Choct & Annison, 1990). The presence of NSP in the gut also affects gut microflora (Choct et al, 1996) and endogenous amino acid loss (Angkanaporn et al, 1994). Solublization of NSP by feed processing causes the formation of gels in the gut that restrict diffusion of nutrients, especially fat, to the gut membrane and reduce the rate of nutrient absorption resulting in reduced growth and feed conversion. Further, reabsorption of water in the hind gut is also negatively affected leading to increased moisture in the droppings (Choct, 2000).
Predicting the energy of cereals for broilers was not possible by classical techniques using caecectomised roosters (Sibbald, 1976, Farrell, 1978) as they digest NSP-containing cereals more efficiently than broiler chicks. Estimating the apparent metabolisable energy (AME) of grains for broilers has traditionally required a chick bioassay of which a number of variations have been published (eg Scott et al 2008). However, a rapid NIR-based technique has recently become available in Australia that can be used to predict the AME of wheat, triticale, barley, sorghum, oats and corn (Black et al, 2009).
Differences in the AME of cereals caused by varying levels of NSP can be moderated by adding carbohydrase enzymes to the diet. Exogenous feed enzymes are included in the mix or sprayed onto feed post-pelleting and have been shown to overcome these problems (Bedford, 2000). Heat stable forms of these enzymes are available from a number of suppliers that allow pelleting of feeds at up to 90oC. Exogenous enzymes are now routinely used in poultry diets containing the cereals wheat and barley and also more frequently in diets based on corn and sorghum, especially those that contain high levels of soybean meal.
When formulating enzymes into broiler diets nutritionists can be confident that the product will improve the digestibility of nutrients and that there will be a predictable enhancement of the energy value of the grain and hence the diet (Cowieson et al 2006). The economic value of the AME enhancement is considerably higher than the cost of the enzyme.
Any dietary minerals present in excess have to be excreted and this process generally involves removal via the kidneys. This requires water and by definition more water than normal. As urine and faeces are combined in chickens the droppings become wetter (Collett, 2007).
Increasing diet levels of the macro minerals Na, K, Cl, Ca and P has been shown to increase water intake and litter moisture (Francesh and Brufau, 2004). Formulating diets to optimise performance requires higher levels of Na and K than those necessary to prevent deficiencies so the levels that result in high rates of weight gain may also increase water consumption and litter wetness (Borges at al 2003). Dietary electrolyte balance (DEB) is calculated in meq/kg of diet according to the equation (Na+K-Cl). These authors showed that growth and FCR were optimised with DEB levels of 240 meq/kg. However, water intake and litter moisture increased linearly with DEB. Nutritionists use alternative sources of Na such as NaHCO3 and Na2SO4 to increase DEB by reducing Cl concentration thereby allowing lower levels of salt addition.
High levels of K can result from formulating high amino acid broiler diets in the presence of phytase. This is largely due to soybean meal which contains more than 2% K (Novus, 1992). High inclusions of vegetable protein meals are necessary to reach amino acid requirements in the presence of phytase. Meat and bone meal is reduced and largely replaced by soybean meal, further elevating the K level. Canola meal can be used to reduce dependence on soybean meal especially in grower and finisher phases after 14 days of age. Limiting K impacts both amino acid levels and DEB, because soybean meal inclusion is limited, but may be achieved with increased use of synthetic amino acids. Lysine, methionine and threonine are important in corn-soy diets, whereas in wheat-based diets synthetic isoleucine and valine may also become economic under these circumstances.
One example commonly found in commercial practice is the involvement of exogenous phytase in episodes of wet litter in broilers (Cowieson, 2011). Phytase catalyses the removal of PO4 from phytate (IP6), the major form in which P is stored in plants. Hence poultry diets containing plant derived ingredients such as grains, milling by-products and vegetable protein meals contain 0.2-0.3% P as phytate (Ravindran et al, 1994). Phytate strongly binds Ca and other mono and divalent cations making them unavailable to the animal at neutral or alkaline pH. Inclusion of exogenous phytase in the diet enables the hydrolysis of the phosphate ester bonds in the gastric portion of the gut. Breaking the phosphate ester bonds releases bound minerals such as Ca. If dietary levels of Ca are too high it will be in excess and must be excreted. As a result water intake is increased and droppings are wetter. Consequently, phytase suppliers recommend that nutritionists allow for this extra Ca release when formulating with phytases and have suggested matrix values for Ca as well as P. Two suppliers also recommend using a matrix value for Na in broiler diets for similar reasons. Cowieson (2011) listed the common ways in which formulation with phytase is misapplied (Table 1).
Table 1. Some common formulating mistakes with Phytase (in order of importance).
- Only using a P matrix
- Using a high P matrix and a low Ca matrix
- Failure to monitor phytate-P concentrations
- Linear dose assumptions for phytase
- Failure to use a Na matrix (especially in high Na diets)
- Failure to monitor Ca and P source effects
- Lack of understanding of limestone quality.
Limestone sources vary in calcium concentration and low Ca limestone sources often contain Mg, which creates an excess of Mg in the diet and leads to wet litter. It is vital to know the purity of the limestone source being used.
Increasing levels of dietary protein increases water consumption in broilers such that a 2% increase in protein level increased water:feed ratio by more than 20% (Marks and Pesti, 1984). Deamination of amino acids in excess of requirements for protein synthesis releases ammonia nitrogen that must be excreted. One other factor in common was that soybean meal contributed to increased protein in some experiments. This led to a conclusion that the increase in water intake may have been due to increased K intake from the soybean meal (Francesh and Brufau, 2004).
Care must be taken when formulating at high amino acid levels to avoid excess crude protein that may result from trying to meet all essential amino acid requirements relative to lysine. Cost becomes a factor and the cost of placing an upper limit on crude protein must be weighed against the likelihood of causing wet litter. Formulating to digestible amino acid levels can also reduce crude protein. Use of the synthetic amino acids isoleucine and valine may be economic if wet litter resulting from excess crude protein becomes an issue.
The presence of mycotoxins in feed has been associated with wet litter in broilers. In particular, ochratoxin, citrinin and oosporin damage the kidney and compromise its ability to concentrate urine. Ochratoxin A causes acute proximal tubular epithelial necrosis in the kidney leading to polyuria and wet litter (Brown et al, 2008). Detection of mycotoxins requires sophisticated analytical techniques which have been expensive and limited in scope in the past. New analytical services offered by commercial companies can quantitatively detect many more mycotoxins and at a more reasonable cost.
Purchase of raw materials without mycotoxin is the obvious way to avoid this problem but when all available grain is contaminated control of mycotoxin in poultry feed can be achieved by addition of products that bind or deactivate mycotoxins in the gut of the chicken. (Huwig et al, 2001). Experience in commercial practice has shown that application of mycotoxin binders is successful in reducing the symptoms of mycotoxicosis and restoring performance to normal levels (Bruerton, 2001).
A common factor of the strategies outlined here is that all require accurate knowledge of the nutrient and anti-nutrient content of the raw materials. That knowledge is fundamental to control of the nutrient levels in the diet. With that in mind the key nutrition strategies for keeping the litter dry are:
- Take advantage of exogenous enzymes to improve nutrient digestibility and to reduce the effect of anti-nutrients. Understand how enzymes affect mineral digestibility and make appropriate adjustments to formulations.
- Understand the mineral content of ingredients and set appropriate limits to prevent excess water intake.
- Avoid excess crude protein in feed by understanding the digestible amino acid content of raw materials and maximizing the use of individual amino acids.
- Monitor ingredients for the presence of mycotoxins and use binders where appropriate.
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