The milk and milk products from cows reared under grazing system are believed to be healthier and hence have high demand compared to milk from cows reared in the non-grazing system. However, the effect of grazing on milk metabolites, specifically lipids has not been fully understood. In this study, we used acetonitrile precipitation and methanol:chloroform methods for extracting the milk metabolites followed by liquid chromatography–tandem mass spectrometry (LC–MS/MS) run to identify the different metabolites between the milk of grazing and non-grazing early lactating Malnad Gidda cows. Various carbohydrates, amino acids, nucleosides and vitamin derivatives were found to be differentially abundant in grazing cows. A total of 35 metabolites were differentially regulated (fold change above 1.5) between the two groups. Tyrosyl-threonine, histidinyl-cysteine, 1-methyladenine, l-cysteine and selenocysteine showed fold change above 3 in grazing cows. The lipid profile of milk showed a lesser difference between grazing and non-grazing cows as compared to polar metabolites. To the best of our knowledge, this is the largest inventory of milk metabolomics data of an Indian cattle (Bos indicus) breed. We believe that our study would help to emerge a field of Nutri-metabolomics and veterinary omics research.

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The expression of genes related to lactogenesis in peripheral blood mononuclear cells (PBMCs) are less understood. To understand the biology of milk production in early lactating non pregnant cows in the blood, the transcriptome from PBMCs was analysed by RNA sequencing. We are able to generate a total of ~ 62.5 Gbp RNA-Seq data files (~ 24 million to ~ 35 million paired-end reads per sample) from high yielder (3) and low yielder (3) of Deoni and Hallikar breeds of Bos indicus (12 samples). The blood sample was collected from twelve early lactating non pregnant cows, the transcriptome from PBMCs was analysed by RNA sequencing. The QC passed reads were aligned against Bos taurus reference assemblies by using HiSAT2 alignment tool. An average of 79.25% and 74.28% reads were aligned in Deoni and Hallikar breeds, respectively. Amongst 85 genes were significantly differentially regulated between low yielder and high yielder of Deoni cows. On contrary, in Hallikar 492 genes were significantly differentially regulated between groups. Transcripts related to CSN gene family (CSN1S1, CSN1S2, CSN2 and CSN3) and FASN were significantly expressed in High yielders of Deoni cows. However, in low yielding Deoni cows and all Hallikar cows, these CSN gene family and FASN gene expression levels were poor or not at all expressed. However, the ATP2B4 (PMCA - Plasma membrane Ca2 + ATPase) gene is expressed only in Hallikar cows. Majority of the genes in lactating Deoni and Hallikar cows were linked to milk protein composition especially caseins, milk fat, lactose synthesis in milk and apoptosis activity in mammary glands. Our findings provide new insights into the understanding of molecular mechanism of differential milk yield among Bos indicus breeds. We believe that our study would be helpful in lactation biology and genetic selection.

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