Effect of a total mixed ration diet on the concentration of amino acid-derived volatiles in milk.

摘要

The flavour chemistry of milk from Holstein-Friesian cows of two genotypes fed total mixed rations (TMR) or pasture has been compared over three years. Mean concentrations of selected milk aroma compounds, namely skatole, indole, dimethylsulphide, toluene, and of total p-cresol (determined after hydrolysis of conjugates) were significantly lower (10 to 39% of pasture treatment, P < 0.01) in the milk from the TMR-fed cows. Mean milk non-protein nitrogen (NPN) and dietary crude protein content (CP) were lower (93 and 67% of pasture treatment, respectively) for the TMR diet. These results are consistent with an origin for these aroma compounds in the degradation of dietary protein amino acids in the rumen. However, concentrations of total m-cresol, which is not thought to derive from dietary protein, were also lower in the milk from TMR-fed cows (19% of pasture treatment). In addition, for the pasture treatment, the patterns of variation of concentrations of skatole, indole and p-cresol and NPN in milk and of dietary CP differed considerably between different periods within a dairy season. These findings indicate that factors additional to CP supply are important in the metabolism of these flavour compounds.