Utilize este identificador para referenciar este registo: http://hdl.handle.net/10400.5/1654
Título: Restrição da suplementação com xilanases em períodos específicos do ciclo produtivo de frangos alimentados com dietas á base de trigo
Autor: Figueiredo, Ana Alexandra Mota
Orientador: Lordelo, Maria Madalena dos Santos
Palavras-chave: broilers
xylanases
wheat
enzymes
frangos de carne
trigo
suplementação enzimática
Data de Defesa: 2009
Resumo: The use of exogenous enzymes in animal feeding has been very important in the last two decades. Enzyme supplementation in cereal based diets for birds suppresses the animal’s deficiencies in endogenous enzymes, mainly in the first stages of life. This increases feed digestibility, improves growth and allows for a better use of low–cost feed ingredients. Cereal grains contain non-starch polysaccharides which increase digesta viscosity in monogastric animals. A more viscous digesta makes the access of digestive enzymes to substrates difficult and limits nutrients absorption resulting in a reduction of nutrients and energy availability to birds. To degrade wheat NSP and to reduce its negative effects, xylanases may be utilized. Wheat is an important source of energy in broiler diets but it presents a great nutritional variation. Enzymes allow for a considerable reduction of the variability between samples of wheat. In addition, the use of xylanases allows for an increase in apparent metabolizable energy and improvement of bird’s performance. Most of wheat varieties contain relatively low contents of soluble polysaccharides and in these cases the animals have the capacity to adapt to the weak increase of digesta viscosity by increasing the digestive enzyme secretion. In addition, in these situations, the main effect of feed enzymes will only be apparent at later stages of growth, as a consequence of improved efficiencies of microbial fermentations in the caeca or even through changes in microbial caeca populations. This latter effect could lead to a decreasein the number of detrimental populations that might flourish at later stages of animal growth in the last compartments of the gastrointestinal tract. Therefore, when supplementing wheat based diets with xylanase throughout the entire life, performance was significantly different only in the last weeks. Thus, we want to know if it will be necessary to supplement wheat based diets with xylanase in the first weeks. For this reason, the objective of this study is to evaluate if xylanase supplementation of wheat-based diets can be restricted to the later periods of animal life decreasing enzyme supplementation costs to the producer. One hundred and sixty one day-old male commercial broiler chicks were fed a wheat based diet supplemented in specific weeks or not supplemented with a commercial xylanase. Feed consumption and individual body weights were recorded weekly. At the end of the experiment, 8 birds from each treatment were killed, digesta were collected from the various gastrointestinal compartments for viscosity and enzymatic activity measurements and the dimensions of the digestive organs were measured. Data were subjected to ANOVA according to the general linear models procedure. Duncan’s multiple-comparison procedure(SAS Institute, 2001) was used to detect significant differences. Differences were considered significant when P < 0.05 There were significant differences on body weight between birds fed no enzyme (W0) and birds fed enzyme supplemented diets for the entire 4 weeks (W4) on the third and fourth week. In the first week the birds fed enzyme-supplemented diets for only the last week (W1) had lower body weight due to a lower feed intake due to difficulty accessing the feeders, however this difference disappeared during the second week. Concerning feed intake, it was not different between treatments throughout the experiment. In first week, the weight gain was lower in birds fed enzyme-supplemented diets for only the last week (W1) due to a lower feed intake. In third week, weight gains improved when enzyme was added throughout the entire life (W4) in comparison to the others treatments with exception of treatment W2 (enzyme in last 2 weeks). This tendency was maintained in following week. Regarding the total weight gain, birds were bigger when fed enzyme supplemented diets for the entire 4 weeks (W4) compared to birds fed unsupplemented diets (W0), birds fed enzyme-supplemented diets for only the last week (W1) and birds fed enzyme-supplemented diets in the last 3 weeks (W3). In the third week and overall, feed conversion ratio improved when enzyme was added throughout the entire life (W4) in comparison to unsupplemented birds (W0). In the fourth week, birds fed enzyme-supplemented diets had also better feed conversion ratio than birds on unsupplemented diets. The viscosity of the digesta of the different compartments of the gastrointestinal tract was not significantly different between treatments. The results show that the relative dimensions of digestive organs were not significantly different between treatments. Although the results of the birds fed enzyme-supplemented diets with restriction of xylanase supplementation in the animal’s performance tend to being better than the ones of the treatment without enzyme, we cannot reduce its period of use under the penalty to penalize bird’s performance. Therefore, it may not possible to reduce the enzyme supplementation costs. In the present study we can state that, even though the effects of xylanase supplementation are more clear at later stages of the bird’s development, it is important to supplement wheat based diets with xylanase for the entire production cycle.
Descrição: Mestrado em Engenharia Zootécnica - Produção Animal - Instituto Superior de Agronomia
URI: http://hdl.handle.net/10400.5/1654
Aparece nas colecções:BISA - Dissertações de Mestrado / Master Thesis

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