Impact of Inoculants and Quality of Silage on Milk

Project entitled:

Prevalence of Microorganisms in Silage and Raw Milk and their Impacts on Dairy Product Quality

Denis Roy, Gisèle LaPointe, Yvan Chouinard


  • Milk is a major staple for human consumption.
  • Raw milk also presents an environment that can be contaminated by thermo-resistant flora and spores from fodder and indigenous flora.
  • The microbiological quality of milk is therefore a major commercial issue and a constant technological challenge both on farms and in plants.
  • Silage is humid fodder that is preserved through the addition of lactic acid bacteria innoculants.
  • These aromatic lactic acid bacteria can have an undesirable impact on milk acidification and on the organoleptic quality of processed dairy products.
  • Twenty-four farms divided into 5 groups that are representative of the primary cow feeding methods were sampled two times to determine the prevalence and diversity of the microbiota of silage and raw milk.
  • The lactic acid bacteria selected from 1,400 isolates from silage and raw milk from the 24 farms will be tested for their resistance to heat treatment and their contribution to the production of volatile compounds during the production and ageing of cheddar cheese.
  • The anticipated results will help producers identify the best silage management practices in order to optimize the microbiological quality of milk and help processors control the sources of microbial contaminants.



  • General objective: Determine the prevalence and diversity of the microbiota of silage and raw milk and their impacts on the organoleptic quality of dairy products.
  • Hypothesis 1: Estimating the diversity and prevalence of bacteria will allow us to know if the use of lactic acid bacteria innoculants in silage is responsible for the presence of indigenous flora that alter milk.
  • Hypothesis 2: Aromatic lactic acid bacteria that are resistant to heat treatment are responsible for the production of undesirable volatile compounds in cheeses


Results and potential benefits

In terms of new knowledge:

  • Impact of different types of silage in a cow’s diet on the microbiological quality of raw milk
    • Better identify and quantify the microorganisms that are present and active.
    • Better understand the transfer rate of bacteria and mycetes from silage to milk.
    • Better understand the role of lactic acid bacteria innoculants on the processing of milk into cheese.
  • Effects of milk’s indigenous flora on the organoleptic properties of processed dairy products
    • Better understand the relationship between the organoleptic characteristics of processed milk and the heat-resistant bacteria of interest or bacteria causing alterations.
    • Predict the specific metabolic characteristics (thermoresistance and the production of bacteriocins) through the comparative analysis of the genome of isolated lactic acid bacteria.

Potential Benefits:

  • Economic
    • Optimization of the microbiological quality of milk used in cheesemaking
    • Control of the organoleptic quality of dairy products
  • Environmental
    • Reduction in numbers of rejections of poor-quality processed dairy products
  • Social
    • Maintaining quality standards for milk and dairy products


Professionals trained

Mérilie Gagnon (doctorat): Phenotypic and genotypic characterization of isolated lactic acid bacteria in silage and raw milk: antibacterial activity, thermoresistance and the production of volatile compounds.

Alexandre Jules Kennang Ouamba (doctorat): Comparative analysis of the prevalence and phylogenetic structure of microbial communities in silage and cow milk.


Financial contributions

Partnership for innovation in dairy production and dairy processing (EPI2011-2017):

  • Fonds de recherche du Québec – Nature et technologies
  • Ministère de l’Agriculture, des Pêcheries et de l’Alimentation du Québec
  • Novalait

Canada Research Chair on Lactic Cultures Biotechnology for Dairy and Probiotic Industries