Influence of ensiling forages at different dry matters and silage additives on lipid metabolism and fatty acid composition

Abstract

White and red clover silages have been shown to result in a higher transfer efficiency of polyunsaturated fatty acids (PUFA) to the milk or meat of ruminants compared to ryegrass silages. For red clover this has been related to protein bound phenols formed by polyphenol oxidase (PPO). PPO is typically active in red clover and the protein bound phenols, which are the result of PPO activity, could result in a decrease in PUFA biohydrogenation in the rumen through inhibition of lipolysis in the silage and/or in the rumen, as lipolysis is a prerequisite of biohydrogenation. Higher transfers of white clover PUFA have been associated with increased rumen outflow rates, although lower in silo lipolysis also has been observed. No research on effect of ensiling agricultural practice as dry matter (DM) and using different silage additives on extent of in silo lipolysis has been performed earlier. Therefore, the goal of this experiment was to study the effect of formic acid, an inoculum or a carbonate buffer as a silage additive and DM content of the wilted forages at ensiling on fatty acid (FA) composition and lipolysis in silages of red clover, white clover and ryegrass. Furthermore, it was attempted to link lipase activity measured as the p-nitrophenyl butyrate hydrolyzing activity of a protein extract with in silo lipolysis and to study the correlation of this enzyme activity with the amount of protein bound phenols. Higher DM content at ensiling resulted in lower linolenic acid concentrations, which was suggested to be related to the longer wilting period and more extensive oxidation. Formic acid resulted in a lower lipolysis in all forages compared to the other treatments. The effect of DM content was rather limited, although lipolysis decreased slightly with increasing DM content in ryegrass. Lipolysis was lower in silages of red and white clover compared to ryegrass at 300 g DM/kg. At higher DM contents lipolysis was equal or lower in ryegrass silages. Enzyme activity measurements indicated bound phenols could inhibit enzyme activity, both in red and in white clover. However, no direct link between measured plant lipase activity of wilted forages and in silo lipolysis could be found.