The effect of different dietary levels of DL-methionine and DL-hydroxy analogue on the antioxidant status of young turkeys infected with the haemorrhagic enteritis virus.

BACKGROUND: The results of experiments involving broiler chickens and turkeys indicate that increased dietary methionine (Met) levels may improve the antioxidant protection of tissues in fast-growing birds. This is an important consideration since viral infections induce oxidative stress. The aim of this study was to verify the hypothesis that turkey diets with increased Met content can suppress oxidation processes induced by infection caused by the haemorrhagic enteritis virus (HEV), and that the noted effect is determined by the chemical form of this amino acid: DL-methionine (DLM) or DL-hydroxy analogue of Met (MHA). RESULTS: Dietary Met content above 40% higher than the level recommended by the NRC (1994) intensified lipid peroxidation in the small intestine, leading to an increase in malondialdehyde (MDA) and lipid peroxide (LOOH) levels, but it also stimulated antioxidant mechanisms in the blood and liver of turkeys infected with HEV. In comparison with DLM, MHA contributed to more severe symptoms of oxidative stress, such as elevated MDA levels in the intestines, and a decrease in glutathione peroxidase (GPx) activity and ferric-reducing ability of plasma (FRAP). CONCLUSIONS: In HEV-infected turkeys, diets with increased Met content did not exert a clear antioxidant effect, which was noted in uninfected birds. The prooxidant activity of Met observed in the small intestinal wall was suppressed in the blood and liver of turkeys, most likely due to intensified synthesis of uric acid and glutathione. In comparison with MHA, DLM had a more beneficial influence on the analysed parameters of the redox status in the small intestine, blood and liver of turkeys.

The effect of different dietary levels of dl-methionine and dl-methionine hydroxy analogue on the antioxidant and immune status of young turkeys.

The hypothesis postulating that the antioxidant and immunological effects of dietary methionine (Met) in young turkeys (1-8 weeks of age) can be differentiated by level and source of Met was investigated in this study. A total of 544 female Hybrid Converter turkeys were divided into four groups and fed diets in which Met content was tailored through supplementation with dl-methionine (dl-Met) or dl-methionine hydroxy analogue (MHA) to levels recommended by NRC (1994) (Groups dl-MetL and MHAL) and exceeding them by 50% (Groups dl-MetH and MHAH). Regardless of its source, the increased dietary Met content led to significantly higher body weight gains but had no effect on feed conversion rates. Moreover, an increased Met content lowered lipid peroxide concentrations in breast meat and increased selected indicators of the plasma antioxidant status like uric acid levels, activity of superoxide dismutase (SOD), glutathione (GSH) concentrations, the ferric-reducing ability of plasma (FRAP), increased immunoglobulin A (IgA) plasma levels and decreased interleukin 6 levels. In comparison with dl-Met, MHA decreased the activities of SOD and catalase, and GSH concentrations in plasma. A dosage by source interaction revealed that the lower MHA content was associated with the lowest plasma GSH concentrations, FRAP values and activities of SOD and catalase. The higher dietary MHA level resulted for most parameters similar values, except for a decrease in lipid peroxide concentrations and an increase in plasma IgA levels. It can be concluded that an increased dietary dl-Met and MHA content (about 150% of the recommendations given by NRC 1994) not only increased the growth rate of young turkeys but also improved their antioxidant status. MHA appears to be a less desirable source of dietary Met for young turkeys when the inclusion level of Met matches the current recommendations. Therefore, a further debate is needed to establish the dietary requirements for Met in poultry.

The effect of dietary methionine levels on fattening performance and selected blood and tissue parameters of turkeys.

A total of 490 eight-week-old female Hybrid Converter turkeys (body weight 4.11 ± 0.03 kg) were divided into 5 groups with 7 replicates of 14 birds each. For 8 weeks, basal diets were supplemented with methionine (Met) at following levels (weeks 9-12/weeks 13-16 of age): Group 1 - 0.34/0.29%, Group 2 - 0.39/0.34%, Groups 3 and 4 - 0.45/0.38% and 0.51/0.41%, respectively, Group 5 - 0.58/0.47%. Only in the first feeding phase the body weight gain (BWG) was affected by Met levels with the significantly highest BWG in Group 3. No treatment effects were found for feed conversion ratio, carcass yield, carcass composition and meat colour. The blood superoxide dismutase activity was significantly highest in Groups 2 and 3. The concentrations of reduced glutathione in the liver were linearly increased (p = 0.018), whereas the ratio of reduced glutathione to oxidised glutathione was highest in Group 3 (quadratic contrast, p = 0.004). It can be concluded that turkeys from Group 3 (Met levels age depending 15% and 10% above recommendations by NRC) were characterised by a well-balanced physiological response. Attention should be paid to the immune response of birds to higher dietary Met levels: plasma IgA concentrations decreased, whereas IL-6 and TNF-α levels increased in turkeys fed diets with the highest Met content.