Perfil oxidativo e metabolismo ruminal de vacas leiteiras alimentadas com farelo de linhaça

Abstract

Flax meal (FM) is a rich source of antioxidant, and ruminants are able to convert lignans into mammalian lignans in the rumen. However, little information is available on the effects of flax meal supplementation on indicators of oxidative stress in dairy cows, the EL production and the correlation of its concentration among milk and other body fluids when cows were fed flax meal, and which ruminal bacterial would be responsible for SDG conversion into EL in the rumen. Eight rumen cannulated cows were used in a double 4 x 4Latin square design, with four 21-d experimental periods, and fed: a control with no flax meal (FM), and diets with 5%, 10% and 15% FM (on dry matter basis). In a first approach, the oxidative profile was evaluated. The production of TBARS was lower in the milk of cows fed 5FM and 10FM. There was no treatment effect on TBARS production in plasma and ruminal fluid although there was a time effect as shown by the decrease post-feeding in both plasma and ruminal fluid regardless of treatment. DPPH scavenging activity in milk, plasma and ruminal fluid was similar among treatments and decreased overtime for all treatments. GPx activity increased in plasma with FM supplementation. Treatment had no effect on SOD activity in milk, plasma and ruminal fluid. Catalase activity was not modified in milk and ruminal fluid, and did not show consistent results in plasma, because when cows were supplemented with 5 or 10% of FM, CAT activity was increased; however, the inclusion of 15% of FM was similar to the control diet. Regarding the data of ruminal fermentation, Concentrations of EL in urine, ruminal fluid, milk and plasma increased linearly with FM supplementation. Spearman?s correlation coefficients were significant for all comparisons except that only a trend was observed between concentration of EL in urine and that in ruminal fluid before feeding. The highest correlation was observed between EL concentration in ruminal fluid 2 h after feeding and that in milk. Feeding increased proportions of FM in the diet, which may have resulted in greater intake of lignans, had no effect on ß-glucuronidase activity of ruminal fluid and faeces. Unlike to what is observed in non-ruminant animals, results of the present experiment may suggest that the activity of ß-glucuronidase in the rumen is of little importance for the absorption of EL and its transfer in milk and other physiological fluids. Further studies are required to better understand and improve EL production and absorption, which could contribute to enhance animal health and the transfer of antioxidant components in milk. Finally, the third approach was to identify bacterial taxa that potentially play a role in the conversion of plant lignans into enterolactone. The concentration of total bacterial 16S rDNA genes obtained using Q-PCR did not differ among treatments. PCR-T-RFLP based dendrograms revealed no obvious global clustering of the microbiota based on diet. PCR-DGGE did however show clustering by diet within four cows. Bands present following feeding of 15% FM and absent when no FM was fed were sequenced. Sequences revealed that uncultured bacteria belonging to the families Succinivibrionaceae, Alphaproteobacteria and genera Prevotella Succinivibrio, Lachnospiraceae, Bacteroidales, Anaerovorax and strain of Fibrobacter succinogenes, and strain H23 of F. succinogenes may play a role in the conversion of plant lignan into enterolactone in the rumen. Altogether, the results suggest that FM supplementation could improve the oxidative status of Holstein cows in mid to late lactation as suggested by increased GPx activity in plasma. In addition, the ruminal fermentation characteristics and EL production, showed that ruminal pH around 6 is not limiting in the process of EL conversion. The higher correlation observed between ruminal fluid and milk than between plasma and milk, suggest that the rumen may have major contribution to EL concentration in milk than plasma. Future research is needed to provide better understanding of the absorption of EL by ruminants, then increasing its transference into the milk. Furthermore, this study provided information about which bacteria can potentially be investigated for its role in EL production.