LIPOMEC: TOWARDS A BETTER UNDERSTANDING OF RUMINANT MILK LIPOLYSIS THROUGH AN INTEGRATIVE BIOLOGY APPROACH IN MILK AND MAMMARY EPITHELIAL CELLS (MEC) – LIPOMEC

LIPOMEC is a transdisciplinary programme combining zootechnics, integrative biology (omics), biophysics, biostatistics, mathematical modeling to limit lipolysis, «from udder to cheese«.

Lipolysis is an important criterion of milk quality. Since 2012, lipolysis levels in milk are routinely measured in France by inter-professional milk analysis laboratories accredited under the milk quality payment scheme according to an instrumental method based on mid-infrared spectroscopy (MIR). However, this method constructed from herd milks, is not fully adapted to individual milk samples.
During the LIPOMEC program, new prediction equations for lipolysis on individual cow and goat milks have been developed. Potential applications are:
- The estimation of milk lipolysis by MIR at the individual scale (animal) for herd monitoring;
- Its use as a genetic selection criterion in conjunction with other milk quality criteria.
In the cow species, the newly built lipolysis prediction equation has been applied to 348,000 spectra from a database created in the PhenofinLait programme (2008-2013). First results have shown that the heritability of the milk lipolysis trait is moderate to high, which makes it possible to consider genomic selection in the future. Moreover, an effect of breed with regard to lipolysis levels in milk was highlighted and several regions of the genome related to the trait 'milk lipolysis' have been identified, some of which are genes or gene regulatory regions whose involvement remains to be confirmed.
On the other hand, the impact of several farming factors on the milk lipolysis rate was evaluated. The impact of dietary restriction on the rate of milk lipolysis was evaluated in the three ruminant species (cow, goat, ewe) and specificities for each species were demonstrated. In cow, additional experiments have shown the impact of milking frequency and milking interval on the milk lipolysis rate.
Finally, the first results of proteomic analyses in dairy cows allowed to identify molecular signatures of lipolysis in milk, in particular two proteins which could become future biomarkers of lipolysis in milk.

A finalization program for the results obtained during the LIPOMEC program is currently being considered within the consortium. The objective of this finalization program is to reach a TRL (Technology Readiness Level) higher than 7 (TRL 7-9: demonstration and validation of the invention in an operational environment).

The results of the LIPOMEC program have already been highlighted in several oral communications and posters in national (Rencontres Recherches Ruminants (3R) 2020 & 2022) and international conferences (EAAP -European Federation of Animal Science- 2020 & 2022; FAO-CIHEAM 2022 conference, ICAR/Interbull conference, etc.). Several scientific articles are currently considered for publication in peer-reviewed journals. In addition, predictive MIR equations for lipolysis levels in individual cow and goat milk are considered for further valorization.

Milk lipolysis is defined as the hydrolysis of triglycerides, the major component of milk fat. Short-chain fatty acids consequently released in milk are responsible for rancid flavor, unacceptable for consumers, in milk and dairy products. In addition, the presence of partial glycerides impairs milk functional properties such as foaming and creaming abilities. Milk lipolysis, routinely measured by accredited inter-professional dairy laboratories therefore represents an important criterion to assess the quality of milk. High lipolysis indexes in milk lead to appreciable loss of market access for dairy farms. Milk spontaneous lipolysis is a complex interplay between farming practices, animal physiology and animal genetics. In addition, milk induced lipolysis may occur during milking or dairy products manufacturing as results of thermal and/or mechanical shocks during milking and cooling. Lipolysis can thus occur throughout the "milk way", from "udder to cheese". The LIPOMEC employs a multi-actor approach to meet a threefold objective:
? To study the lipolytic system constituted by the lipase, its substrate (the milk fat globule) and a balance of activating or inhibiting cofactors in the three dairy species through the characterization of lipase regulatory networks in milk and/or mammary epithelial cells;
? To establish breeding and feeding strategies those ensure optimal and stable milk quality all year round;
? To develop tools and techniques to monitor and reduce lipolysis all along the "milk way".
Our approach is definitely integrative, including animal science, milk biochemistry, milk biophysics, proteomics, lipidomics, genetics, transcriptomics, cell biology techniques, data modeling, and statistics. Interactions between genetics, physiology, farming practices and technological factors related to the milking process will be considered.
LIPOMEC is the first large-scale integrative project to study the lipolytic system in the milk and mammary gland from ruminant species.