Abstract
In pasture-based systems, there are nutritional and climatic challenges exacerbated across lactation; thus, dairy cows require an enhanced adaptive capacity compared with cows in confined systems. We aimed to evaluate the effect of lactation stage (21 vs. 180 days in milk, DIM) and Holstein genetic strain (North American Holstein, NAH, n = 8; New Zealand Holstein, NZH, n = 8) on metabolic adaptations of grazing dairy cows through plasma metabolomic profiling and its association with classical metabolites. Although 67 metabolites were affected (FDR < 0.05) by DIM, no metabolite was observed to differ between genetic strains while only alanine was affected (FDR = 0.02) by the interaction between genetic strain and DIM. However, complementary tools for time-series analysis (ASCA analysis, MEBA ranking) indicated that alanine and the branched-chain amino acids (BCAA) differed between genetic strains in a lactation-stage dependent manner. Indeed, NZH cows had lower (P-Tukey < 0.05) plasma concentrations of leucine, isoleucine and valine than NAH cows at 21 DIM, probably signaling for greater insulin sensitivity. Metabolic pathway analysis also revealed that, independently of genetic strains, AA metabolism might be structurally involved in homeorhetic changes as 40% (19/46) of metabolic pathways differentially expressed (FDR < 0.05) between 21 and 180 DIM belonged to AA metabolism.
Highlights
In pasture-based systems, there are nutritional and climatic challenges exacerbated across lactation; dairy cows require an enhanced adaptive capacity compared with cows in confined systems
Ghaffari et al.[18] reported that branched-chain amino acids (BCAA) degradation and methyl-histidine metabolism increased during the transition and suggested these changes could be associated with insulin resistance
The aim of this work was to study the dynamic of AA metabolism across lactation stages in relationship with milk production and energy metabolism of grazing dairy cows belonging to NAH vs. NZH genetic strains by using a targeted metabolomics approach on blood plasma
Summary
In pasture-based systems, there are nutritional and climatic challenges exacerbated across lactation; dairy cows require an enhanced adaptive capacity compared with cows in confined systems. Pasture-based dairy systems are gaining scientific interest due to the increasing demand for dairy products associated with lower environmental impact and better animal welfare[1,2] These systems impose restrictive conditions which determine that high genetic merit cows are not able to express their genetic potential for milk yield as their nutritional requirements are not fulfilled due to limited dry matter intake[3]. It has been widely demonstrated that early lactating cows are characterized by a catabolic state of peripheral tissues associated with the uncoupling of somatotropic axis and a state of insulin resistance[8,9] In this regard, grazing dairy cows are confronted with more challenging environments than confined dairy cows which determine that these homeorhetic changes are even more dramatic and last for longer during early lactation[10]. The aim of this work was to study the dynamic of AA metabolism across lactation stages in relationship with milk production and energy metabolism of grazing dairy cows belonging to NAH vs. NZH genetic strains by using a targeted metabolomics approach on blood plasma
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