APSS 2013 Proceedings - The University of Sydney

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Aust. Poult. Sci. Symp. 2013.....24 bone development in chicks exposed to high phytase levels in diets with standard Ca and low dP diets suggests that P availability was low. This may be due to an overestimation in P release at the higher phytase inclusion. As a result, diets were deficient in dP, with proportionally higher available Ca levels, capable of further lowering P availability by rendering nPP insoluble due to cation chelation. At low Ca levels, the low dP levels had a less pronounced effect on weight gain and bone ash compared to the high Ca levels. In turn, the high phytase level did not impede young chick bone mineralisation at the lowest dP levels to the same degree as observed in treatments with the same level of phytase and dP at standard Ca levels. Together this indicates a higher P availability at low Ca levels, supporting previous studies (Rama Rao, et al., 1999; Tamim, et al., 2004; Powell, et al., 2011). Phytase has been shown to enhance energy and protein digestibility, resulting in improvements in BW with reduced FI (Ravindran, et al., 1999; Selle, et al., 2000). In the present study, the significant reductions in BW with 1500 FTU/kg of phytase, in addition to the assumed low P release, may have been due to a shortage of nutrients as a result of the reduced FI and the enzymes failure to compensate by releasing amino acids due to the abundance of Ca cations. At normal dP levels, the low Ca levels resulted in improved growth and litter quality (data not shown) compared to the standard Ca levels. It can be concluded that reducing dietary Ca concentrations, particularly in the grower, finisher diets, results in improved performance of broilers with no change in bone ash (at slaughter weight) especially when offered diets with marginal dP supply. This strategy may be an effective way to reduce diet costs and improve broiler efficiency under commercial production systems. When increasing phytase dosing from 500 to 1500 FTU in formulation with matrix values of 0.96 and 1.69g dP/kg of feed, the risk of reduced FI should be considered. Therefore, in order to improve the consistency of the beneficial effects of higher doses of microbial phytase, dietary reformulation may be required, with particular attention to amino acid and energy concentrations (Cowieson, et al., 2011a). REFERENCES Angel R, Tamim N, Applegate T, Dhandu A, Ellestad L (2002) The Journal of Applied Poultry Research 11, 471-480. Bedford MR (2000) Animal Feed Science and Technology 86, 1-13. Cowieson AJ, Bedford MR, Ravindran V, Selle PH (2011a) British Poultry Science 52, 613- 624. Cowieson AJ, Wilcock P, Bedford MR (2011b) World's Poultry Science Journal 67, 225- 236. Létourneau-Montminy MP, Narcy A, Lescoat P, Bernier JF, Magnin M, Pomar C, Nys Y, Sauvant D, Jondreville C (2010) Animal 4, 1844-1853. Maenz D, Classen H (1998) Poultry Science 77, 557-563. Powell S, Bidner TD, Southern LL (2011) Poultry Science 90, 604-608. Ravindran V, Cabahug S, Ravindran G, Bryden W (1999) Poultry Science 78, 699-706. Selle P, Ravindran V, Caldwell R, Bryden W (2000) Nutrition Research Reviews 13, 255- 278. Tamim N, Angel R, Christman M (2004) Poultry Science 83, 1358-1367. Woyengo TA, Nyachoti CM (2011) Canadian Journal of Animal Science 91, 177-192. 22
Aust. Poult. Sci. Symp. 2013.....24 BIO-EFFICACY OF FEED PROTEASES IN POULTRY AND THEIR INTERACTION WITH OTHER FEED ENZYMES L.F. ROMERO 1 and P.W. PLUMSTEAD 1 Summary The most accepted value of the inclusion of exogenous proteases in poultry diets is the improvement of protein digestibility from dietary ingredients. However, effects of exogenous proteases on animal performance do not necessarily reflect the increment in protein digestibility from proteases in vitro and a variety of factors determine the bio-efficacy of the application of proteases in chickens. An accurate prediction of amino acid digestibility improvements in response to dietary enzymes is important to maximise the animal performance response and ensure that the cost of including the enzyme is justified. Overestimation of the digestibility effect of protease on individual essential amino acids relative to other amino acids may limit the benefits of increments on the absorption of dietary protein for animal growth. A lack of understanding of what effects proteases alone or in combination have on the digestibility of individual amino acids may further imbalance the amino acid profile provided by the diet. It has been recently demonstrated that improvements in the digestibility of amino acids following exogenous protease application in broiler diets can be accurately predicted as a linear function of undigested amino acids in the diet. The contribution of specific proteases in combination with carbohydrase enzymes in terms of protein digestibility has been confirmed. Nonetheless, effects of protease on the digestibility of other nutrients such as fat and fibre, may play a role in determining the in vivo response to protease in chickens. Factors like the age of the birds, the gut health status of the animals, and the profile of gut microbial populations appear to affect the response to proteases in animal performance and require further study. I. INTRODUCTION The use of exogenous proteases in poultry feed has become more prevalent in recent years, following the broader commercial acceptance of other feed enzymes like phytases and xylanases, and increased pressure on the cost of proteinaceous ingredients. Most current commercial proteases for animal feed are alkaline proteases of bacterial origin. Feed cost is reduced with the inclusion of proteases through a reduction of crude protein and first limiting amino acids supplied by dietary ingredients. Nonetheless, the effects of exogenous proteases on animal performance do not necessarily reflect the in vitro digestibility of protein from ingredients, but are influenced by a variety of factors that affect their bio-efficacy. For example, serine proteases in broiler chickens do not appear to show a linear dose response on protein digestibility of complete feeds, but an optimum is present (Argüelles-Ramos et al., 2010), after which marginal reductions with increasing protease doses are evident. This suggests that a balance between the hydrolysis of dietary protein and undefined physiological interactions in the intestine may limit further improvements in protein retention due to protease activity. Effects of exogenous proteases are not only confined to the digestion of protein, but extend to the digestion of other nutrients such as fat and starch. Furthermore, the application of proteases cannot be considered in isolation because it often occurs in combination with other feed enzymes, whose mechanisms and subsequent effects on digested nutrients do not appear to be totally independent to those of proteases. 1 Danisco Animal Nutrition, DuPont Industrial Biosciences, Marlborough UK. luis.romero@dupont.com, peter.plumstead@dupont.com 23
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INTERACTIVE EFFECTS OF EXOGENOUS EN
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AUTHOR INDEX Name Page(s) Email Add
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Klein-Hessling, H 207 hkleinhesslin
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Van de Wouw, A 247 nnet.vandewouw@w
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