Article pubs.acs.org/JAFC
Biohydrogenation of Fatty Acids Is Dependent on Plant Species and Feeding Regimen of Dairy Cows Majbritt B. Petersen*,† and Søren K. Jensen‡ †
AgroTech A/S, Institute for Agri Technology and Food Innovation, Agro Food Park 15, 8200 Aarhus, Denmark Department of Animal Science, Aarhus University, P.O. Box 50, 8830 Tjele, Denmark
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ABSTRACT: Rumen biohydrogenation (BH) of C18:3n-3 (ALA) and C18:2n-6 (LA) has been shown to be reduced in cows fed species-rich herbage, but plant species offering the best protection against BH are yet to be elucidated. The aim of the present study was to investigate differences in rumen in vitro BH of ALA and LA between single plant species and feeding regimens. Rumen fluid was collected from cows fed either total mixed ration (TMR), species-rich silage (HERB), or grass silage (GRASS). Five single species (alfalfa, birdsfoot trefoil, chicory, English plantain, and salad burnet) and a grass−clover mixture (white clover and ryegrass) were incubated in three replicas up to 30 h and subsequently analyzed for fatty acid content. Michaelis−Menten kinetics was applied for quantifying the BH rate. BH proceeded at the lowest rate in alfalfa and salad burnet (P < 0.005), and independent of species BH rate was lower in HERB and GRASS compared to TMR (P < 0.001). KEYWORDS: rumen biohydrogenation, linoleic acid, α-linolenic acid, alfalfa, birdsfoot trefoil, chicory, English plantain, salad burnet, grass−clover mixture
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mixture.13 The effect of single plant species could be one explanatory factor for the observed differences in BH pattern between results of in vivo and in vitro studies using the same herbage, as the in vivo herbage mixture would be highly dependent on the individual cow’s preferences.14 It has also been shown that it is possible to differentiate between FA profile of cheese produced from two alpine pastures differing in botanical composition;4,15 thus, a possible difference in the effect of plant species on BH is highlighted. Therefore, the identification of the single plant species responsible for maximizing rumen bypass of beneficial PUFAs could provide the necessary knowledge to grow pastures with the ideal composition to reach maximum impact on BH of beneficial PUFAs and consequently to increase their content in milk.16 Another hypothesis is that different feeding regimens can have different impacts on the microbial population in the rumen and hence in ruminal BH. Recently it has been shown that a high content of starch in the cow’s diet causes a shift in the normal BH pathway of ALA and LA, indicated by an increase in the rumen content of trans-10 C18 isomers, specifically t10c12 conjugated linolei acid (CLA) and t10 C18:1. This also seems to be accompanied by changes in the bacterial community.17 A typical conventional total mixed ration (TMR) diet with grain and corn silage would likely have higher starch content than common organic diets with clover− grass silage as major roughage. Therefore, a combination of the feeding regimen and the botanical composition of the herbage could have an impact on rumen BH and milk FA composition. Only a few studies have compared the effects of feeding traditional dairy diet (concentrates, corn, and grass silage) or
INTRODUCTION The majority of studies dealing with manipulation of polyunsaturated fatty acids (PUFA) in milk have been performed with PUFA from different oilseeds,1 but recent studies have shown that feeding species-rich semigrasslands2 and alpine pasture3,4 increases the transfer rate of C18:3n-3 (ALA) to milk products compared to feeding pure grass or oilseeds. Milk concentration of ALA from cows grazing at high altitude have been reported in the range of 1.15−2.31 g/100 g fatty acid (FA), whereas ALA in milk from cows on lowland pasture is reported in the range of 0.84−1.65 g/100 g FA,5 although the ALA content in herbages is similar to or even lower than that in the species-rich herbages compared to different grass species.6,7 It has been suggested that the increase of beneficial PUFAs from cows fed species-rich herbage is caused by modification or inhibition of the rumen biohydrogenation (BH), which increases the transfer efficiency from feed to milk of ALA and C18:2n-6 (LA).6,8,9 During traditional feeding
