Abstract
A better knowledge of the bovine milk proteome and its main drivers is a prerequisite for the modulation of bioactive proteins in milk for human nutrition, as well as for the discovery of biomarkers that are useful in husbandry and veterinary medicine. Milk composition is affected by lactation stage and reflects, in part, the energy balance of dairy cows. We aggregated the cow milk proteins reported in 20 recent proteomics publications to produce an atlas of 4654 unique proteins. A multistep assessment was applied to the milk proteome datasets according to lactation stages and milk fractions, including annotations, pathway analysis and literature mining. Fifty-nine proteins were exclusively detected in milk from early lactation. Among them, we propose six milk proteins as putative biomarkers of negative energy balance based on their implication in metabolic adaptative pathways. These proteins are PCK2, which is a gluconeogenic enzyme; ACAT1 and IVD, which are involved in ketone metabolism; SDHA and UQCRC1, which are related to mitochondrial oxidative metabolism; and LRRC59, which is linked to mammary gland cell proliferation. The cellular origin of these proteins warrants more in-depth research but may constitute part of a molecular signature for metabolic adaptations typical of early lactation.
Highlights
Phenotyping animal traits related to performance, quality, welfare and health is often challenging but necessary to meet husbandry and societal expectations
Among the 4654 proteins compiled in the atlas, 95 gene names (GN) (Fig. 1 and Supplementary information Table 1) were detected for all four milk fractions, whereas 93, 488, 15 and 3139 GN were detected in skimmed milk, whey, milk fat globule membrane (MFGM) and exosomes
The 8 major proteins detected in the MFGM, such as mucin 1 (MUC1), redox enzyme xanthine dehydrogenase (XDH), and butyrophilin subfamily 1 member A1 (BTN1A1), were among the list of 95 GN
Summary
Phenotyping animal traits related to performance, quality, welfare and health is often challenging but necessary to meet husbandry and societal expectations. We used the early lactation period as a proxy for NEB because modern dairy cows systematically experience some degree of negative energy balance and extensive mobilisation of body reserves during this period. Proteins could be robust biomarkers of NEB based on their presence or absence in milk or milk fractions during early lactation (all or nothing identification). Because available proteomics data were obtained from different breeds, countries and rearing practices, these proteins may constitute robust biomarkers of NEB, independently of the breed and husbandry practices. To our knowledge, this is the first attempt to reuse the publicly available milk proteome data to propose potential indicators for NEB and for dairy ruminants
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