Effect of cut number, stage of maturity and method of conservation on amino acid contents of forages

The amino acid (AA) contents of 42 forages were analysed. During three consecutive years, forage samples from the first and third cut were collected at two stages of maturity (30 days apart) on the same experimental plots. After cutting, the forage samples were either frozen (-20°C), artificially dried (forced air at 30°C, <45% relative humidity), wilted on the field and subsequently barn dried, field dried, ensiled with a dry matter (DM) content of 30% or ensiled with a DM content of 50%. The method of conservation had no effect on total AA content in DM. However, when considered individually, the contents of certain AA showed significant differences among methods of conservation, particularly between ensiling at 30% DM and the remaining methods of conservation. In silages, a high moisture content associated with an insufficiently low pH, resulted in a pronounced degradation of proteins and modification of the AA profile. Compared to the other conservation methods, ensiling increased the proportion of proline and decreased the proportions of glutamic acid and aspartic acid. Any of the conservation methods could prevent losses of AA. Freezing resulted in the smallest losses, but this conservation method can only be applied in research. For application in practice, careful drying methods proved to be the least damaging.