Breast milk is considered the gold standard of infant nutrition because it contains the essential nutrients to support early infant growth, development and immunity. The sugars in human milk, known as oligosaccharides, play a key role in releasing these beneficial functions. A new project is exploring ways to improve the yield and composition of cow’s milk oligosaccharides, which will ultimately support the sustainable large-scale extraction of oligosaccharides from bovine milk and its whey derivatives.

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This project – known as OPTI-OLIGO – also aims to better characterise the enzymes produced in the mammary gland that lead to the synthesis of oligosaccharides in cow’s milk.

By investigating the factors influencing the presence of oligosaccharides in cow’s milk, Teagasc hopes to optimise their production in milk. When the study is completed, a plan can be developed for targeted breeding strategies to produce milk with a higher composition of oligosaccharides.

Such knowledge, along with the availability of an oligosaccharide pipeline in the form of ‘super-producing’ cows, will have many applications. These include providing dairy processors with an opportunity for functional product commercialisation and higher value-added dairy products for human consumption.

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Why oligosaccharides?

It has been argued that breast milk oligosaccharides:

• Selectively stimulate the growth of beneficial microbiota; 

• Protect against bacterial and viral infection; 

• Promote the maturation of the infant immune system; and 

• Improve brain growth and development.

It is thought that the incorporation of more and more distinct milk oligosaccharides, as they become available at commercial levels, will revolutionise the landscape of paediatric nutrition and offer opportunities to improve infant health worldwide.

However, currently only a limited number of human milk oligosaccharides are added to infant formula despite more than 200 distinct oligosaccharides having been identified in breast milk. Similar oligosaccharides have been found in cow’s milk – albeit at a lower concentration when compared to breast milk.

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Assessing factors of influence

Factors that are thought to influence oligosaccharide expression in cows include seasonality, genetics, feeding, age and parity (the number of times an animal has given birth), stage of lactation and disease state. To assess the effect of these factors on the oligosaccharide milk profile, a large sample set of milk was collected over the course of lactation.

Samples were collected from 199 cows during early, mid and late lactation. The cows included those from the Teagasc Moorepark Next Generation Herd: Holstein-Friesian cows categorised as Elite (top 1 per cent nationally) based on the Irish total merit index, the Economic Breeding Index (n=95); Holstein-Friesian cows representative of the national average, based on EBI (n=60); and high-EBI pedigree Jersey cows (n=44). Samples from all three genotypes were balanced for parity.

It is already known that bovine colostrum – the first stage of lactation – has significantly higher levels of oligosaccharides than any other stage of lactation. Subsequent analysis of early, mid and late lactation samples will determine the quantity of 15 of the most abundant bovine oligosaccharides over one lactation season. This will allow us to determine if the cows producing higher levels of oligosaccharides in early lactation continue to produce the highest levels in mid and late lactation.

Quantifying a broad oligosaccharide profile rather than the quantities of one or two oligosaccharides is important; even though certain oligosaccharides appear in higher abundance, the diversity and interaction between the different oligosaccharides are key characteristics of their functionality. In this respect, we can identify cows that are above average producers of milk oligosaccharides.

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Results that will inform production

To date, oligosaccharide levels in all early lactation samples and many of the mid lactation milk samples have been quantified. In the colostrum samples, Jersey cows were producing the highest levels of the three most abundant oligosaccharides. It was also noted that the elite Holstein Friesians produced more oligosaccharides than the national average Holstein Friesian cows. Interestingly, the majority of the top 10 oligosaccharide-producing cows were in their second parity.

The data generated here will indicate the effect of feed, age and parity on oligosaccharide production. This result will also guide a genome-wide association study (GWAS) investigating the genetic differences in the cows producing high levels of oligosaccharides (‘super producers’) when compared to average and low oligosaccharide producing cows. The GWAS will identify genetic differences both within and between the breeds. After this, proteomic analysis of the milk samples will profile the level of the various enzymes involved in the biosynthesis of oligosaccharides. This information will relate the genetic differences to enzyme and other protein expression and further expand our knowledge of the pathways leading to milk oligosaccharide production.

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This article first appeared in TResearch, Spring 2023.