This experiment was conducted to evaluate the effects of dietary methionine (Met) content on the performance of white commercial laying hens and to determine Met and total sulfur amino acids requirements (TSAA). These requirements were estimated using three statistical models (broken-line regression, exponential and second order equations) to evaluate their abilit to determine amino acid requirements. A total of 216 laying hens (23 wks of age) was used in a completely randomized design (CRD) with six treatments with four replicates of nine birds each. The basal diet contained 15.25% crude protein, 2830.16 kcal/kg ME and 0.24% Met. Synthetic DL-Met was added to the deficient (basal) diet in 0.05% increments to make the other five experimental diets (0.29, 0.34, 0.39, 0.44 and 0.49% Met). Increasing Met level from 0.24 to 0.34% significantly increased egg production, egg weight, egg mass, egg content, and feed intake and decreased feed conversion ratio (p<0.05). However, further Met increases, from 0.34 to 0.49%, no longer influenced these parameters. Out of the three models, the broken-line regression model presented better estimates of AA requirements. Based on broken-line equations, average Met and TSAA requirements of the laying hens were 0.31 and 0.60% (245.50 and 469.25 mg/hen/day) from 22 to 36 wks of age, respectively.

In this study, the effects of the inclusion of different vitamin C levels in the diet on bone mineral density (BMD) and eggshell quality was determined. Four experimental diets with four levels of vitamin C (0, 250, 500 and 750 mg/kg) were used. During the experiment, environmental temperature and humidity were 19±1°C and 55±5% respectively. Correlation coefficients of BMD index and shell characteristics with production parameters were also determined. Egg weight, egg mass, hen-day egg production and eggshell quality were not significantly influenced by vitamin C levels. BMD was not affected by vitamin C utilization. A positive correlation was observed between BMD and egg weight and hen-day egg production. A significant positive correlation between specific gravity and eggshell traits was also found. In conclusion, the results of this study have shown that vitamin C does not affect bone mineral density and eggshell quality under lower critical temperature.