Metabolomic based insights into the milk metabolome

Milk and dairy products are often referred to as a “complete” source of nutrition, combining essential macro and micronutrients which aid the maintenance of health within consumers. Recently, significant innovation has occurred within the dairy industry, resulting in alterations to traditional farm management practices in order to meet global dairy product demand. However, various factors including diet and lactation stage can impact both the production and nutritional composition of associated dairy products. Therefore, the objective of this thesis was to use a metabolomics-based approach, to study alterations occurring in the milk metabolome as a result of lactation stage and dietary regime, and subsequently to investigate the impact of these factors on associated dairy products and the animal themselves. Firstly, the impact of lactation stage on the metabolite composition of wholemilk powder was examined. The results led to the identification of an early lactation metabolite signature in wholemilk powder, associated with an increase in phospholipid and triglyceride levels, as lactation progressed. Examining the impact of diet on dairy products is best achieved through controlled interventions. We capitalised on a well-controlled intervention study, and obtained wholemilk and buttermilk samples from cows fed different dietary regimes: perennial ryegrass (pasture), total mixed ration (TMR) or partial mixed ration (PMR), consisting of both pasture and TMR diets. Dietary regime significantly affected the metabolite composition of both wholemilk and buttermilk samples. In wholemilk powder, the triglyceride compound class was significantly altered by dietary regime, with polyunsaturated triglycerides significantly higher in pasture-derived samples. Moreover, significantly different metabolites in buttermilk samples included phospholipids and sphingomyelins, with significant phospholipids mainly polyunsaturated in nature. Further analysis of the bovine ruminal fluid metabolome of cows fed the different diets, again highlighted the influence of diet on the metabolomic profile, with short chain fatty acids, sugar related metabolites and amino acids significantly different between the samples. Examination of commercial samples is difficult due to lack of clarify of both feeding regimes, and lactation stage. However, as a first attempt we compared Irish and international dairy products, namely cheese and butter. Some differences were observed, in particular with the amino acid profile between the sample groups. However, further work is needed to expand this comparison.
In conclusion, this thesis demonstrated the impact of lactation and diet on the metabolite composition of milk and dairy products. Distinct changes were observed, and future work will need to harness this information. In particular, future work will need to determine if alterations in pasture derived products translate into health benefits, following human consumption.