Javascript is required to view this map.

Learning Research Service Volunteer Engagement

Off-flavours in milk occur at a low incidence in all milk-producing areas of Canada, with "outbreaks" occurring periodically in certain localities, often for no clearly defined reason. In the late 1990s, the incidence of off-flavours in bulk-tank milk was unacceptably high in PEI, with 50/330, or 15% of herds, affected during the winter season of 1999-2000.

A study was initiated and, as a first step, the reliability of the milk transport personnel in identifying off-flavours in milk was evaluated using a sensory study. It was concluded that, in the absence of a more objective diagnostic tool, the use of trained milk graders is appropriate for field monitoring of flavour quality of bulk-tank milk, especially where a simple “accept/reject” decision is required.

Off-flavour cases were more common during the fall and early winter months, and were concentrated in the intensive dairy farming regions (Queens and Prince Counties). High-rate clusters tended to receive more precipitation than low-rate clusters, confirming a field observation that off-flavour incidents were associated with stormy weather.

It was established that a transmitted (feed) flavour was the defect responsible for the outbreak, and that its occurrence was strongly associated with the following factors: feeding round-bale silage to lactating cows; feeding stored forage less than 2 hours before milking, or as a free-choice; poor air quality where milking cows were housed.

Feeding lactating cows with freshly opened baled grass silage less than three hours before milking was shown to trigger the development of feed off-flavour. The occurrence of this off-flavour could be predicted biochemically by concentration differences of either dimethyl sulfide or butane-2-one. However, the off-flavour was probably due to subtle concentration differences of a variety of volatile aromatic compounds, rather than the presence or absence of any specific compounds.

These results have given rise to several hypotheses. The volatile compounds responsible for the transmitted flavour defect are likely to be normal fermentation products found in silage, but present in baled timothy at higher than normal concentrations. Baled timothy silage may be more likely than other silages to elaborate these fermentation products because of the slow fermentation that occurs when grasses such as timothy, with naturally low sugar content, are baled without chopping or adequate conditioning. This may allow growth of certain microorganisms that elaborate the aromatic compounds in question. These microorganisms would normally be inhibited by the more rapid lowering of pH typical of most chopped silages.

A pilot study for the development of an instrument-based diagnostic assay was conducted; results showed that a gas-sensor array had a very high discriminative ability and repeatability in assessing the flavour quality in the small number of samples tested, and this method of detection should be further investigated.

A range of options for reducing the incidence of off-flavour are discussed. More detailed information can be obtained from the thesis accompanying this report.

[Results were presented to the PEI dairy producers at meetings and through reports and newsletters. Several peer-reviewed publications resulted. The incidence of feed-flavour rejections has decreased markedly, to just a few each season, primarily as a result of the recommendations from this research, giving a huge return on investment for the dairy industry -- a real success story]