Characterization of the bovine milk proteome in early-lactation Holstein and Jersey breeds of dairy cows

Abstract

Milk is a highly nutritious natural product that provides not only a rich source of amino acids to the consumer but also hundreds of bioactive peptides and proteins known to elicit health-benefitting activities. We investigated the milk protein profile produced by Holstein and Jersey dairy cows maintained under the same diet, management and environmental conditions using proteomic approaches that optimize protein extraction and characterization of the low abundance proteins within the skim milk fraction of bovine milk. In total, 935 low abundance proteins were identified. Gene ontology classified all proteins identified into various cellular localization and function categories. A total of 43 low abundance proteins were differentially expressed between the two dairy breeds. Bioactive proteins involved in host-defense, including lactotransferrin (P=0.0026) and complement C2 protein (P=0.0001), were differentially expressed by the two breeds, whereas others such as osteopontin (P=0.1788) and lactoperoxidase (P=0.2973) were not. This work is the first to outline the protein profile produced by two important breeds of dairy cattle maintained under the same diet, environment and management conditions in order to observe likely true breed differences. This research now allows us to better understand and contrast further research examining the bovine proteome that includes these different breeds.

Biological significance: Within the last decade, the amount of research characterizing the bovine milk proteome has increased due to growing interest in the bioactive proteins that are present in milk. Proteomic analysis of low abundance whey proteins has mainly focused on human breast milk; however, previous research has highlighted the presence of bioactive proteins in bovine milk. Recent publications outlining the cross-reactivity of bovine bioactive proteins on human biological function highlight the need for further investigation into the bovine milk proteome. The rationale behind this study is to characterize and compare the low abundance protein profile in the skim milk fraction produced from Holstein and Jersey breeds of dairy cattle, which are two major dairy cattle breeds in the USA. A combination of fractionation strategies was used to efficiently enrich the low abundance proteins from bovine skim milk for proteomic profiling. A total of 935 low abundance proteins were identified and compared between the two bovine breeds. The results from this study provide insight into breed differences and similarities in the milk proteome profile produced by two breeds of dairy cattle.

Keywords: Bioactive proteins; Low abundance proteins; Whey.

Fig. 1

Heat map presentation of peptide counting data of the 935 proteins identified. Cluster analysis was performed in JMP (Pro 10) using the ward method where the differentially expressed low abundant proteins were assembled into their GO functional groups. Clustering was based on peptide counts in Holstein and Jersey cow skimmed milk. Bar color represents peptide count data where dark red represents higher expression and blue color represents lower expression.

Fig. 2

Hierachical clustering of the 43 significantly differentially expressed protein within bovine skim milk between Holstein and Jersey cattle. Analysis was performed in JMP (Pro 10) using multivariate clustering. Bar color represents peptide count data where dark red represents higher expression and blue color represents lower expression.

Fig. 3

Summary of methods and results from proteomic studies analysizing the low abundant whey protein profile in milk.