Abstract
A study was conducted to evaluate the effects of dietary total sulphur amino acids (TSAA) to lysine (Lys) ratio on performance of Ac layers (black-boned chicken). A total of 800 laying hens from 38 to 50 weeks old was allocated according to a completely randomized design with five treatments and 20 replicates of 8 birds each. The basal diet was formulated with 16% crude protein (CP), 2755 kcal/kg of metabolizable energy (ME), 0.482% methionine, 0.925% TSAA and 1.12% lysine. The TSAA/Lys ratio of the basal diet was 0.85. The basal diet plus four diets were formulated, two with TSSA levels at 10% and 20% below and two at 10% and 20% above that of the basal diet, giving 0.762%, 0.857%, 1.047% and 1.142% TSAA, respectively with the basal at 0.925% TSAA. The 10% decrease or increase in TSAA from 0.952% did not affect feed intake or egg production. However, further TSAA decreases from 0.857% to 0.762% led to reducing egg weight, which increased with a curvilinear trend as the level of TSAA in the diets was increased. TSAA influenced nitrogen retention in a quadratic trend, with hens fed diets containing 0.952% and 1.047 % TSAA retaining more nitrogen than the other treatments. Increasing dietary TSAA increased the white and yolk index and Haugh unit, whereas egg shell thickness, yolk colour and egg components were not influenced. The TSAA/Lys ratio of 0.85 improved egg weight and nitrogen retention of Ac layers. Keywords: Egg weight, feed intake, performance, production, nitrogen retention, sulphur amino acid
Highlights
Ac chicken is a native black-boned breed that is characterized by white feathers, skin, meat and bones, which is kept in the Mekong Delta of Vietnam
The total sulphur amino acids (TSAA)/Lys ratio did not influence the intake of feed, protein, lysine or metabolizable energy (ME)
The TSAA/Lys ratio did not affect egg production (P = 0.78), while egg weight increased as the TSAA content of the diet increased from 0.762% to 0.857%
Summary
Ac chicken is a native black-boned breed that is characterized by white feathers, skin, meat and bones, which is kept in the Mekong Delta of Vietnam. This breed has a small body size (0.9 kg), and is kept for meat and egg production. The Ac chicken has potential in meat and egg production because of its good flavour and relatively high price. The growth performance and egg production of Ac chicken are low compared with those of commercial breeds. According to Phuong & Thien (2008), because they are kept in a scavenging system, Ac egg production is low with 90 - 95 eggs/year, though it could be improved to 180 - 190 eggs/year (Phuoc et al, 2016a) by providing good nutrition and disease control
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