High stocking density (STD) could affect duck welfare and production. The objective of our study was to investigate whether dietary tryptophan (TRP) supplementation could alleviate the detrimental effects of high STD on ducks. White Pekin ducks at 4 to 6 wk of age were raised at 11 birds/m(2) and fed diets containing 0.18, 0.48, 0.78, or 1.08% TRP for 21 d. Growth performance, concentrations of TRP and metabolites in the blood and hypothalamus, antioxidative activities in serum and tissue, meat quality, serum uric acid, and urea nitrogen were measured. Weight gain and feed efficiency were significantly improved by TRP supplementation at ≥ 0.48 and ≥ 0.78% (P < 0.05 and P < 0.001, respectively). Serum TRP, hypothalamic TRP, 5-hydroxytryptamine (5-HT), 5-hydroxyindoleacitic acid (5-HIAA), and 5-HIAA/5-HT were also increased significantly (P < 0.01). These increases plateaued at 0.48% TRP, and no further improvement was obtained by adding more TRP to the diet. Dietary TRP supplementation significantly increased levels of total antioxidant capacity, glutathione peroxidase (GSH-Px), and catalase (CAT) in serum; GSH-Px in liver; and GSH-Px and CAT in breast muscle (P < 0.05). Malondialdehyde levels in breast muscle decreased (P < 0.001). Drip loss of breast muscle and pH decline at 45 min postmortem were reduced by TRP supplementation (P < 0.01 and P < 0.05, respectively). Meat color was similar among different treatments (P > 0.05). Breast muscle shear force was increased significantly when dietary TRP level increased to 1.08% (P < 0.01). For ducks raised at 11 birds/m², dietary TRP supplementation could alleviate stress and improve growth performance, antioxidative activity, and meat quality.

Aims: To investigate the changes in fermentation quality of whole-plant corn silage ensiled with varying dosages of mixed organic acid salts (MS), and link these dosage changes to shifts in bacterial composition. Methods and Results: Fermentation quality and bacterial community of corn silage ensiled with MS at four application rates (0, 0Á67 g kg À1 , 1Á33 g kg À1 , and 2Á00 g kg À1 ) were investigated. The MS consisted of 40% potassium sorbate and 60% sodium benzoate. The corn silages were conserved for 42 days. Dry matter losses and ammonia nitrogen concentration were linearly declined by up to 19Á10 and 33Á3% with increasing dosages of MS. MS treatments significantly reduced the pH of silage vs the control group. Further analysis indicated that the improvement of fermentation quality was the result of shifts in bacterial composition, the relative abundance of Lactobacillus paralimentarius and Pediococcus spp. increased while Lactobacillus reuteri, Lactobacillus coryniformis and Klebsiella declined with increasing dosages of MS. Conclusions: MS effectively improved the fermentation quality of whole-plant corn silage with an optimum dosage of 2Á00 g kg À1 .Significance and Impact of the Study: The correlation between bacterial taxa and fermentation quality provides a potential for the development of novel silage inoculants and for the application of MS on controlling Klebsiella mastitis of livestock farms.

Aims: To investigate the effects of ohmic heating (OH) and water bath heating (WB) on the membrane permeability, membrane structure, intracellular organization and leakage of intracellular substances of Escherichia coli O157:H7 at the same inactivation level and at a heating temperature of 72°C. Methods and Results: Flow cytometry analysis indicated that membrane permeability of E. coli O157:H7 by OH was comparable to WB at 72°C. Scanning electron microscopy analysis showed that the OH-treated E. coli O157:H7 had greater morphological changes than those of WB-treated ones both at the same inactivation level and the same heating temperature. Transmission electron microscopy analysis showed that both OH and WB caused severe damage on the intracellular organization of E. coli O157:H7 at 72°C. Moreover, OH-treated E. coli O157:H7 had more leakage of intracellular substances than those treated with WB due to the electroporation caused by OH. Conclusion: OH presents considerable potential in inactivation of E. coli O157:H7, especially OH at 10 V cm À1 with a much shorter heating time. Significance and Impact of the Study: The nonthermal effect of OH had a greater effect on the cell membrane of E. coli O157:H7, resulting in more pores and more leakage of intracellular substances out of the E. coli O157:H7 cells. These results could promote the application of OH in food processing.

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