Determining the factors that cause higher concentration of conjugated linoleic acid (CLA) in milk fat of dairy cows fed fresh alfalfa versus alfalfa hay

Much attention has been given to conjugated linoleic acid (CLA) due to its anticarcinogenic properties. Dairy products are one of the major sources of CLA in human diets. Dietary management of dairy cows to increase CLA in milk may be beneficial for the dairy industry. Several researchers have reported that grazing animals produce a higher percentage of CLA in milk fat when compared to animals fed TMR diets; however, the reason for this observation is uncertain.; In the first two experiments, the effect of storage on the profile of fatty acids (FA) from fresh alfalfa was determined. The samples were stored at -20°C for 60 days and the profile of FA was estimated in Experiment 2 based on the results from Experiment 1. After flash-freezing alfalfa samples with liquid N just after harvesting, the percentage of total FA did not change.; I proposed that the higher sucrose concentration in fresh forages results in higher vaccenic acid (VA) flow to the duodenum, the main factor responsible for high milk CLA. Experiment 3 was conducted to test the hypothesis that supplemental sucrose increases the percentage of VA in the effluent of continuous culture fermenters. The pattern of biohydrogenation (BH) of FA from fresh alfalfa or alfalfa hay supplemented with three concentrations (0, 4, and 8%) of sucrose was studied at a constant pH of 6.2. Four continuous culture fermenters were used in a 4 x 4 Latin square design. Fresh alfalfa increased total BH of FA compared to hay. Vaccenic acid concentration in the effluent was almost three times higher for fresh alfalfa compared to alfalfa hay and was the predominant 18:1 isomer, whereas trans-10 18:1 was 50% lower for fresh alfalfa. Total BH and BH of linoleic and linolenic acids linearly decreased with sucrose. The effects of sucrose on BH and concentration of VFA may have been caused by a shift in microbial population by mechanisms that are independent of pH.; In Experiment 4, the interaction effect between sucrose and pH on BH was evaluated in vitro. I also developed a multi-compartmental model to estimate pool size and flux of vaccenic acid during BH of FA in fresh alfalfa. There was no effect of sucrose addition on the disappearance rate of 18:2 and 18:3. Also, there was no effect of sucrose on the estimated BH of vaccenic acid.; In conclusion, sucrose is not the main cause of the higher CLA in milk fat of dairy cows fed fresh as opposed to preserved forage. However, the pH-independent effect of sucrose on BH should be further investigated by quantifying the changes in microbial species. Using compartmental kinetics to study BH can provide new information on the rate constants of the intermediates of BH.