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Current breeding strategies and their consequences for animal health, animal welfare and the environment are major societal concerns, both in ethical and sustainability terms. The longevity of ruminants depends on the expression of phenotypes linked in particular to production traits (such as milk yield and milk quality) and health-related characteristics (such as mammary inflammation). Variability in the expression of a given phenotype may depend not only on genetic factors, but also on non-genetic factors, such as epigenetics.

The aim of recently published work has been to document the contribution of epigenetics to animal health and longevity. The strategy adopted is based on the development of a mouse model of mammary inflammation to study epigenetic markers linked to early inflammation and lactation, and their persistence over successive lactations. Mammary glands in 1st or 2nd lactation, with or without inflammation, were harvested and used for DNA methylation (RRBS) and gene expression (Fluidigm RT-qPCR) analyses.

In addition to the effect of early inflammation on the DNA methylation status of mammary tissue, the impact of this inflammation in 1st or 2nd lactation was assessed. This work highlighted the importance of health history in 1st lactation during 2nd lactation.

Our work also showed that the effect of lactation rank on mammary DNA methylation is stronger than the effect of early inflammation. Moreover, only a few differentially methylated regions are common to the effects of lactation rank and inflammation, highlighting the specific regulatory responses of epigenetic modifications according to the physiological changes studied.

This project assessed the effects of early mammary inflammation and successive lactations on gene methylation and expression over the lifetime of the animal. Knowledge was acquired in a mouse model, with the aim of transferring this knowledge to farmed species. This work has opened up new avenues that could lead to proposals for new levers to be used in breeding.

Contact :

• Fabienne Le Provost