Species-specific characteristics of variables associated with milk lipolysis induced by a feed restriction in cows, ewes and goats.

Milk lipolysis in ruminant species is a major issue because it affects milk quality and its ability to be processed. Previous studies have showed that comparable levels of dietary restriction significantly increase milk lipolysis in dairy cows, whereas they reduce milk lipolysis in ewes and have no effect in goats. This study identified a set of variables statistically linked with milk lipolysis regardless of the dairy species. Three experimental studies were performed to explore the effect of a similar dietary restriction on milk lipolysis in 3 ruminant species: cows (n = 44), ewes (n = 48) and goats (n = 24). These experiments consisted of a 2 × 2 crossover experimental design with 2 treatments: "unrestricted" (NR) with animals fed 100% DMI ad libitum and "restricted" (REST), with animals fed 65% DMI ad libitum. A set of 79 parameters related to milk yield and composition, blood metabolites, and milk lipolysis were assayed to enable both intra-species as well as inter-species analyses across the 3 ruminant species. For the former, correlations between variables were studied within each of the 3 species. For the latter, 2 approaches were considered. First, a redundancy analysis (RDA) was performed for the integrative exploration and visualization of association trends between parameters, dietary restriction groups, and lipolysis levels across species. Second, the Multivariate INTegrative method (MINT) was applied to explore latent structures and shared covariance patterns identify across species and linked with lipolysis using the performances, milk and plasma parameters. The RDA showed: i) a strong separation of the REST and NR groups as well as the low and high lipolysis groups, and ii) that all species respond consistently to feed restriction, indicating a shared metabolic response to treatment. Our integrative exploratory analysis of variables reports strong treatment × species interaction, since associated with milk lipolysis, the response to feed restriction is markedly divergent among species. Notably, milk urea is associated with high lipolysis in cows. MINT does not provide visual evidence of robust cross-species latent structures and shared covariance pattern related to lipolysis. The mobilization of adipose tissue differed between species during feed restriction. This was evident in the range of body lipids mobilised and, consequently, in the nutrient-sparing pathways, such as urea production. This may partly explain why species respond differently to milk lipolysis.