effect of oxidized soybean oil against pomegranate seed as antioxidant on the in vitro rumen fermentation parameters

introduction oxidative stress is an inevitable consequence of intensive production due to mismatched balance between free radical production and natural antioxidant capacity of animals. reactive oxygen species (ros) refers to a group of free radicals produced by oxidative energy cycle and also recently demonstrated to be as a weapon for macrophage cells. moreover, feed processing phenomena such as extruding and pelleting is one of the major sources of ros production in feed due to lipid peroxidation and notably oxidation cascades in unstable organic matters of feed. although ros could be a source of adverse effect on fiber degradation in the gut of ruminant by reducing microbial population counts and diversity, because rumen bacterial, protozoal and fungal community as well as eukaryotes are susceptible to oxidative damages. therefore, using plant or feed base antioxidant in the diet of dairy animals would be necessary in further feeding strategies. the aim of this study was to evaluate antioxidant capacity of pomegranate seed against the adverse effect of peroxide content of feed that induced by supplementation of oxidized soybean oil as energy and fiber source in preparturient dairy goats. materials and methods the gas production experiment and batch culture degradability test were carried out to investigate the effects of fresh soybean oil (fso), oxidized soybean oil (oso) and biologically active constituents of pomegranate seed (ps) on microbial fermentation characteristics, kinetics of gas production, methane and carbon dioxide production, in vitro dry matter degradation (dmd), t 0.5, and lag time. also, the calculated parameters e.g. microbial protein, molar proportion of volatile fatty acids, metabolizable energy (me), and organic matter digestibility (omd %) were evaluated for different treatments. the parameters were analyzed through the completely randomized design with repeated measurements. the treatments were 1) base diet and fso (4% of dry matter (dm)), 2) base diet and oso (4% of dm), and 3) base diet, oso and milled ps (8% of dm). the oso contained higher peroxide value (7.06 vs. 1.37 gram millieqivalent /kg oil), and more trans fatty acid isomers than fso. results and discussion oso reduced total gas production, t 0.5, dmd, microbial protein, me, omd%, total carbon dioxide production, molar production of propionate, and moles numbers of total volatile fatty acids and increased the methane production, lag time, and molar proportion of acetate and butyrate when compared with fso. adding ps as antioxidant increased the total gas production, t 0.5, dmd, me, omd %, total carbon dioxide production, molar productions of propionate and acetate, and moles numbers of total volatile fatty acids, and reduced the lag time, methane production and molar proportion of butyrate significantly. the major observed effect of oso that is important from an economical point of view in ruminant nutrition was reduced dm degradability. depressed dm intake, negative energy balance, metabolic disorders and susceptibility to microbial disease and inflammation are expected in this oxidative situation. also environmental importance of increased methane production by progressive effect of free radicals in proton partitioning in to methane production pathway in the rumen are significant, but could be improved by ps supplementation. ps may play a protective role against oxidized oil via flavonoids, polyphenols, special fatty acid contents, carotenoids and other bioactive compounds well documented in herbal medicine. conclusion in general, oso feeding quantitatively and qualitatively reduced positive parameters of microbial fermentation, dmd, microbial protein synthesis and vfa production but ps diminished the adverse effects of oso and fso feeding significantly. it seems that the ps has potential antioxidant compound reducing the harmful ros effect on microbial metabolism in the rumen as well as reducing progressive peroxidation cascades in feed and animal body.