Abstract
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.
Highlights
India is blessed with a large number of cattle (193.46 million) population[1] and ranks first in the world in total milk production (187.7 MT)[2]
Milk derived from the pasture system has been found to have higher unsaturated fatty acids and more levels of α-tocopherol and β-carotene compared to Total Mixed Ration (TMR) diets[16]
Our study indicated that the pasture based feeding system had brought significant changes in the polar metabolite profile in the milk rather than the non-polar lipidomic profile in Malnad Gidda cows
Summary
India is blessed with a large number of cattle (193.46 million) population[1] and ranks first in the world in total milk production (187.7 MT)[2]. Intensification in the dairy industry resulted in the inclination of the feeding practices towards non-grazing (zero-grazing/stall-fed) system where cows are housed indoor and mainly fed with paddy straw and cultivated green fodder along with concentrates which enables the farmers to have better control over nutrition, health and management of lactating animals[6]. O’Callaghan et al.[6] have observed the beneficial influence of the grazing system on the nutritional composition of milk and milk products (butter and cheese) both at macronutrient and fatty acid levels (conjugated linoleic acid and omega 3 fatty acid). Metabolomics signatures associated with milk of grazing cows could be used to identify potential candidate biomarkers for differentiating the origin of milk-based on the feeding systems. The present study was conducted on Malnad Gidda cows to see the effect of pasture (grazing) and stall-fed (non-grazing) based feeding management systems on milk metabolites
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