ARI Volume 2 Number 1.pdf - Zoo-unn.org

UCHEWA, Emmanuel Nwafoagu et al. 268iron and potassium thereby reducing mineralsolubility and availability (Erdman, 1979). Whenacted upon by phytase enzyme, these cations arereleased much like phosphorus. Consequently,increased availability of these minerals will result inincreased retention of phosphorus in chicken givenphytase. In contrast with nitrogen, phosphorusgenerally remains in association with the surfacelayer of soil. This limits the extent to whichphosphorus pollutes the ground water (MAFF,1996). Soil erosion or manure run-off from the soilsurface, however, can result in appreciablequantities of phosphorus entering the waterways.The presence of excess nutrients in suchwaterways invariably leads to pollution.Nitrogen: Excess nitrogen present in manure is ininorganic form (often as ammonium ion NH + 4 ).Some may be lost to the atmosphere as ammonia(NH 3 ) (MAFF, 1996). Because of its positivecharge, NH +4 tends to associate electrostaticallywith the soil particles. This renders much of theapplied nitrogen initially immobile in the soil.However, some of the NH +4 in the soil, whichremains unassimilated by plants, is subsequentlyconverted to nitrate in the soil. Although aproportion is converted to nitrogen gas (N 2 ) by theprocess of denitrification, much of the nitrate willfind its way into ground water supplies (Headonand Walsh, 1994).Although quantitatively, nitrogen andphosphorus represent the major pollutants presentin animal wastes, several other waste constituentscan have adverse environmental effects.Increasing concern has been voiced by many withregard to the quantities of minerals derived fromanimal faeces released in the environment (AFRC,1991).NUTRITIONAL APPROACHES TO REDUCEPOLLUTION FROM ANIMAL WASTESA number of nutritional approaches may bepursued which can help reduce the pollutive effectof animal waste (Vandergrift, 1992). In thisregards, in piggery attention has been focused onreduction of nitrogen and phosphorus in the faecalmatters, while maintaining health and highperformance of the pigs. Nutritional managementcan substantially reduce the quantity of nitrogenand phosphorus excreted by pigs (VanKlooster etal., 1998).Dietary manipulation designed to increasefeed digestibility reduces the qualities of manureproduced by an animal (MAFF, 1991). Inclusion ofprobiotics in the diet may also assist the animal toutilise dietary nutrients more efficiently(Goransson, 1997). The presence of pathogens orpotential pathogens (coliform) in the gut canrender digestion and absorption of nutrients lesseffective. This in turn results in excessive excretionof such nutrients in the faeces (Van’t Klooster etal., 1998).The addition of specific enzymes to dietsmay also solve specific nutritional problems. Feedenzymes can reduce the levels of nitrogen andphosphorus excreted in the faeces. Phytaserenders phosphorus in the form of phytic acid,which is biologically available to the animal(Cromwell, 1980). Cellulases and protease may beused to enhance digestion of fibrous andproteinacious dietary components (Tamminga andVerstegen, 1992). Glucanases and pentosanasesmay be employed to destroy anti-nutritivemolecules such asglucans and pentosans (Headonand Walsh, 1994). Anti-nutritional factors generallyhave an adverse effect on digestion and onassimilation. Their removal, therefore, exerts apositive effect on these physiological processes.Ammonia is one of the most noxiouspollutants associated with animal waste(Tamminga and Verstegen, 1992). Build up ofammonia concentrations in animal pen has adetrimental effect on both animals and animalkeepers alike. Excess of ammonia into theatmosphere has an obvious pollutive effect (Hornand Squire, 1997). Beal et al. (2001) has shownthat pre-treatment of pigs diet with proteaseincreased the in vitro digestion of nitrogen inweaner pigs. There are four reasons why enzymesmay be added in certain diets:1. To remove or destroy anti-nutritional factors2. To enhance overall feed digestibility3. To render certain nutrients biologically available4. To reduce the pollutive effect of animal excretesReducing Phosphorus Excretion throughNutrition: Inclusion of microbial phytase in pigdiets is one of the initial successes in the utilizationof enzyme to solve specific nutritional problem.Phytase currently represents the most excitingpotential application of enzyme in the animal feedindustry (Nasi, 1990). Two thirds of thephosphorus in cereal grain is in form of phyticacid, (phytate). This form of phosphorus isbiologically unavailable to monogastric animals, asthey do not produce digestive enzyme (phytase)capable of releasing the phosphate groups fromphytate (Bateman, 1998).Jongbloed et al. (2000) stated that since1990 various experiments with exogenousmicrobial phytase have been reported to quantifytheir effect on the apparent digestibility/availabilityof phosphorus. One of the first and mostinteresting experiments was the dose-responseeffect of microbial phytase (Natusphos ® ) on theapparent digestibility of phosphorus in growingpigs from 20 to 55 Kg (Beers and Jongbloed,1992). Six doses of phytase (from 0 to 1800FTU/Kg) were used in two types of grower’s diets