Crude protein reduction, digestible amino acids digestible lisine ratios and lysine levels in diets for Nile tilapia fingerlings / Redução de proteína bruta, relações aminoácidos digestíveis com a lisina digestível e níveis de lisina digestível em rações para alevinos de tilápia do Nilo

AUTOR(ES)
DATA DE PUBLICAÇÃO

2006

RESUMO

The current study was aimed at evaluate the effect of dietary crude protein reduction with amino acids supplementation and determine the requirements of methionine plus cytine, threonine and lysine, based on the ideal protein concept, in diets for reverted Nile tilapia fingerlings (Oreochromis niloticus), of the thailand line. Four trials were carried out at the fish nutrition laboratory of the Animal Science Department of the Federal University of Viçosa. The fishes were maintained into 36 aquariums of 130 liters supplied with single-pass flow-through water and aeration, controlled temperature and they were fed ad libitum six times per day. Performance parameters, corporal composition, the daily protein and fat deposition rates and nitrogen retention efficiency of the fishes were evaluated. The first experiment was carried out during 40 days aimed at evaluate the effect of dietary crude protein (CP) reduction with amino acids supplementation, based on the ideal protein concept. Three hundred and ninety six fingerlings with average initial weight of 0.80 0.17 g were used. The treatments had consisted of six isoenergetic and digestible isolysinic diets (1.50%) with different levels of CP (31.0; 31.0; 30.0; 29.0; 28.0; and 27.0%). Fishes fed 27.0% CP diet showed lower feed:gain ratio, lysine efficiency for growth, nitrogen intake and humidity body and higher proteic efficiency for growth and fat body. It was concluded that the CP level for Nile tilapia fingerlings can be reduced four percentage points (32.0 to 28.0%) with no negative effect on performance since rations are supplemented with limiting essential amino acids. The second experiment was carried out during 40 days aimed at determine the requirement of digestible methionine plus cystine, based on the ideal protein concept. Three hundred and ninety six fingerlings with average initial weight of 0.86 0.02 g were used. The treatments had consisted of five diets with different digestible methionine plus cystine:lysine ratios (59.5; 63.5; 67.5; 71.5 and 75.5%) and digestible threonine:lysine ratio of 80%; and one diet with the digestible methionine plus cystine:lysine ratio of 75.5% and digestible threonine:lysine ratio of 85.0%, all of then were isoenergetic, isoproteic and digestible isolysinic (1.40%). The increase of the dietary digestible methionine plus cystine:lysine ratio did not affect the studied parameters, except the body fat and humidity content, of which the effect was quadratic, with quadratic maximal and minimum at 66.95 and 66.74%, respectively. However, the increase of the dietary digestible threonine:lysine ratio in diets with digestible methionine plus cystine:lysine ratio of 75.5% improved the feed conversation ratio, the nitrogen retention efficiency and protein and lysine efficiency for growth. It was concluded that the total or digestible dietary sulfur amino acid level of 0.91 and 0.86%, that correspond to a total and digestible methionine plus cystine:lysine ratio of 57.2 and 59.5%, respectively, provided the best results of performance and carcass characteristics of Nile tilapia fingerlings. The third experiment was carried out during 30 days aimed at determine the nutritional requirement of digestible threonine, based on the ideal protein concept. Four hundred thrirty two fingerlings with average initial weight of 1.64 0.03 g were used. The treatments had consisted of five diets with different ratios of digestible threonine:lysine (69.0, 74.0, 79.0, 84.0 and 89.0%) and digestible methionine plus cystine:lysine ratio of 70.0%; and one diet with the digestible threonine:lysine ratio of 84.0% and digestible methionine plus cystine:lysine ratio of 75.0%, all of then were isoenergetic, isoproteic and digestible isolysinic (1.35%). The increase of the dietary digestible threonine:lysine ratio affected just the feed intake, the body protein level and the daily protein deposition rates, that have increased linearly. However, the increase of the dietary digestible methionine plus cystine:lysine ratio did not affect the studied parameters. It was concluded that the dietary level of total or digestible threonine for the best results in Nile tilapia fingerlings for performance parameters is of 1.11 e 0.99% and, for corporal protein deposition is 1.43 and 1.28%, which correspond to a total and digestible threonine:lysine ratio of 71.0 and 69.0% and of 90.0 and 89.0%, respectively. The forth experiment was carried out during 30 days aimed at determine the requirement of digestible lysine, based on the ideal protein concept. Four hundred thirty two fingerlings with average initial weight of 1.12 0.02g were used. The reatments had consisted of six diets with different digestible lysine ratios (0.95; 1.10; 1.25; 1.40; 1.55 and 1.70%), all of then were isoenergetic and isoproteic. The increase of the dietary digestible lysine did not affect the survival rate and the body fat level of the fishes. However, all the others parameters had improved linearly, except the lysine utilization efficiency and the body humidity, which got worse quadraticly and linearly, respectively. It was concluded that the level of total or digestible lysine is 1,80 (0.600%Mcal of DE) and 1,70% (0.567%Mcal of DE), respectively, provided the best results of performance and carcass characteristics of Nile tilapia fingerlings, when the ideal protein concept was used in the experimental diets formulation.

ASSUNTO(S)

aminoácidos sintéticos ideal protein nutricao e alimentacao animal sintetic amino acids oreochromis niloticus tilapia proteína ideal oreochromis niloticus tilápia

ACESSO AO ARTIGO

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