Factors affecting the occurrence of cyclopropane fatty acids in grass silage

Haymilk and haymilk products meet the consumers expectations about traditional and sustainable dairy farming and have gained increasing interest in some parts of Europe. In haymilk production, among other restrictions, fermented feed is not allowed in the ration of cows. Recently, advancements in analytical methods applicable to dairy products have emerged, enabling the detection of silage utilization in animal diets. Notably, cyclopropane fatty acids (CPFAs), such as dihydrosterculic acid (DHSA) (cis 9,10-methylene octadecanoic acid) and lactobacillic acid (LBA) (cis-11,12-methylene octadecanoic acid), have been identified as biomarkers capable of distinguishing between Grana Padano and Parmigiano Reggiano cheeses. Silage is permitted in the production of the former but prohibited for the latter. Consequently, these biomarkers allow authentication by confirming the absence of silage in the animals' diet. CPFAs are known to be produced by some microorganisms during fermentation in silage production, thus they are expected to occur only in milk of animals fed silage. Most of the previous studies in this area referred to lowland areas, where the fermented part of the dairy cows' diet typically consists of maize silage. However, in the mountainous areas of the Alps (Europe) the diet often includes on-farm produced grass silage, which only recently came to the attention of research concerning the authentication of dairy products based on a silage-free diet. In this work, grass silage was produced under controlled conditions to test the formation of CPFAs depending on the growth cycle (cut), fermentation temperature and the use of fermentation starters. In addition, 69 silage samples of several farms were collected and studied to investigate the relationship between silage quality and the CPFAs content under on-farm conditions in the local practice. The concentration of CPFAs were found to be differently affected by the temperature, depending on the cut, whilst the starter only marginally affected CPFAs. A positive relationship between acetic acid and CPFAs was observed both in laboratory-produced silages and in on-farm collected grass and maize silages. These results provide a first insight into the presence of CPFAs in grass silage and its association with fermentation parameters adding new helpful information in using CPFAs as markers to authenticate milk from a silage-free diet. • Cyclopropane fatty acids (CPFAs) were found in 91 % of laboratory-produced grass silage samples. • CPFAs were detected in 100 % and 75 % respectively of on-farm maize and grass silages. • CPFAs were differently affected by temperature, depending on the grass sample. • CPFAs were only marginally affected by the starters. • A positive relationship between CPFAs and acetic acid was observed.