Rumenic acid studies with

The anti-diabetic effect of CLA may depend on both species and types of isomer. Rumenic acid seemed to be inactive (Martin Valeille, 2002), but the role of Irans-10,cis-12 isomer is controversial some studies verified decreasing glucose levels and increased insulin sensitivity with increased intake of lrans-10,cis-l2 CLA (see the review by Khanal, 2004), while others reported opposite effects - that is, the promotion of insnlin resistance (Khanal, 2004 Moloney, Yeow, Mullen, Nolan, Roche, 2004 Wang Jones, 2004). 

Interestingly, only the 10t,12c-18 2 increased the stearic acid content at the expense of 18 ln-9, which suggests an alteration in A9 desaturase activity. This observation was further confirmed by in vitro studies. Lee et al. (8) reported that CLA depressed the expression of stearoyl-CoA desaturase (SCD) mRNA. These effects were correlated with a decrease in the 16 1/16 0 and 18 1/18 0 ratios in mice liver, which are considered to be indices of A9 desaturation. Moreover, studies conducted with pure rumenic acid suggested that this effect on SCD was due mainly to other conjugated fatty acid isomers. Bretillon et al. (9) demonstrated that... 

Oxidative Metabolism. Because CLA are fatty acids, they are substrate for energy production through oxidative metabolism. However, few studies have been conducted to consider this metabolic pathway. One study was published on carbon dioxide production during 24 h after a bolus intragastric delivery of labeled CLA isomers compared with linoleic acid (16). It appeared (Fig. 15.2) that both CLA isomers studied were more oxidized than linoleic acid. In that study, 70% of the radioactivity was recovered as CO2, a value close to what was previouly observed with linolenic acid (17). However, when looking at the mechanisms involved in mitochondrial oxidation, Clouet et al. (18) showed that mitochondrial respiration with rumenic acid was lower than that with linoleic acid. These difference between both fatty acids may be due to a lower camitine-acylcamitine translocase activity. 

In an in vitro fermentation study, rumen microorganisms metabolized both isomers of [ C]DDT o,p- and p,p-) to the corresponding DDD isomers at a rate of 12%/h. With p,//-DDT, 11% of the C detected was an unidentified polar product associated with microbial and substrate residues (Fries et al., 1969). In another in vitro study, extracts of Hydrogenomonas sp. cultures degraded DDT to DDD, l-chloro-2,2-bis(/5-chlorophenyl)ethane (DDMS), DBF, and several other products under anaerobic conditions. Under aerobic conditions containing whole cells, one of the rings is cleaved and p-chlorophenylacetic acid is formed (Pfaender and Alexander, 1972). 

Previously it was reported (41) that dry heating of alfalfa at lOS C for up to 1440 min resulted in a reduction of in vitro organic matter digestibility (IVOMD) by rumen microbes. Increases in Acid Detergent Insoluble N (ADIN) and Neutral Detergent Fibre (NDF) were also observed. For the convenience of the reader these data have been included with more recent observations in this study. 

Rumen Strain. In studies on strain Ml of M. ruminantium isolated from bovine rumen contents, we confirmed the results of Smith and Hungate (17), showing that this species requires factors present in rumen fiuid (23). It would not grow in medium containing H2-CO2, bicarbonate, sulfide, cysteine, yeast extract, trypticase, and minerals unless rumen fiuid was also added. In further experiments (23) we assayed fractions of rumen fiuid using the above medium and showed that growth factors could be separated into two components by acidification and ether extraction. One factor was not extractable with ether, and others were shown to be volatile acids. 

The products were also tested by in-vivo techniques. For example, evaluation of the rumen stability was carried out using samples placed in porous nylon bags and incubated in the rumen and in the intestine of cows. In other experiments, the products were given orally to the animals and the levels of amino-acids in the GI tract and in the blood plasma were measured. The impact of the protected amino-acid intake on the quality of the milk production was also studied in collaboration with institutes and universities in different countries. The increase of protein production is significant (0.9 g to 1.7 g / liter / animal) and economically interesting for dairy farmers. The higher levels of protein in milk also improve cheese manufacturing. 

One study compared three commercial-feed-grade magnesium oxides with differing reactivity s and particle sizes by measuring the solubiliztion of Mg in acid solution and rumen fluid (Xin et al., 1988). Xin found that the finer, more reactive MgO was more readily soluble in both acid solution and rumen fluid. 

---