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Impact of cow pasture diet and breed on the fat fraction of milk and dairy products in seasonal, spring-calving dairy production system
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Date
2025
Authors
Kostovska, Renata
Journal Title
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Publisher
University College Cork
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Abstract
Pasture-based cow feeding systems, relying mainly on perennial ryegrass (PRG), require significant use of chemical fertilizers, and introducing multispecies swards (MSS) aligns with the EU's Farm to Fork strategy, which aims to reduce fertilizer dependency and enhance biodiversity by 2030. However, despite the associated sustainability benefits of the MSS diet, there is a lack of evidence regarding its impact on milk and dairy product quality in seasonal, spring-calving dairy production systems. This PhD thesis fills this gap by comparing, throughout lactation, the effects of a conventional PRG monoculture to those of an MSS diet on the composition and quality of milk from spring-calving Holstein-Friesian (HF) and Jersey Holstein-Friesian (JFX) cows, which are the two main breeds in Ireland. The work then extends to assessing the impact of diet and breed on high-fat dairy products quality.
Chapter 1 consists of a literature review focusing on the effects of different pasture-based diets, including perennial ryegrass (PRG), a mixture of PRG and white clover (PRG-WC), and multi-species swards (MSS), on milk yield, general milk composition, and fatty acid (FA) profile. In Chapter 2, this PhD work highlighted the differences in milk yield, composition, and physico-chemical properties of milk samples deriving from the four groups (PRG HF, PRG JFX, MSS HF and MSS JFX) across the entire lactation. Overall, cow breed had a prominent effect on the properties studied. In particular, JFX milk had lower yield, but increased protein, total solids and fat levels, compared to HF milk. A typical seasonality curve was observed, where the yield of milk decreased from early lactation to LL, and the levels of protein, fat and total solids increased. Milk fat globule size was impacted mainly by cow breed and globules were larger in milk derived from JFX cows. A diet effect on milk fat globule size was observed in late lactation (LL), where the milk derived from MSS cows exhibited larger globule size compared to PRG milk.
Chapter 3 covered the impact of the three primary production factors on the detailed milk fat fraction, which is the most susceptible to variation due to changes in cow diet. While the polar lipid profiles were mainly affected by stage of lactation (SOL), the FA profile of milk was affected by diet, cow breed and SOL. Indeed, a diet effect was observed in mid-lactation and LL, where MSS milks showed higher polyunsaturated (PUFA) levels, compared to PRG milks. Both diets resulted in milk with desirable linoleic/α-linolenic acid ratios of around 1. PRG-derived milk was higher in trans-FA and branched-chain FA, particularly for the HF breed. PRG HF milks had higher oleic acid proportions and lower spreadability index values, compared with all the other groups. A breed effect was demonstrated in LL; the milk of JFX cows tended to have increased de novo FA levels, compared with HF.
In addition, the potential for application of Raman spectroscopy to classify milk samples based on the three factors examined (diet, breed, and SOL) was demonstrated in Chapter 4, and a prediction model for unsaturation index of milk based on Raman spectra and chemometrics models were developed.
In Chapter 5, the impact of diet and breed on UHT-treated whipping cream was studied. The observed variation in the FA profile across the different groups studied in milk, particularly in nutritionally beneficial PUFA and trans-FA, was also reflected in the FA composition of whipping cream. From a techno-functional perspective, when JFX cows were fed on PRG, oleic acid levels were lower compared to the rest of the groups, suggesting a breed by diet interaction. Compared to the other groups studied, the PRG JFX group had a larger MFG size, and exhibited more desirable characteristics from a consumer point of view, such as shortest whipping time and increased foam firmness. Cow breed had a more prominent effect on the organoleptic properties assessed, compared to diet. In particular, the JFX breed showed higher b* coordinates and ß-carotene levels in cream.
Chapter 6 examined the properties of butter, based on diet and breed factors. The FA profile was impacted by diet, and this factor impacted the PUFA and trans-FA families, as described for milk and whipping cream. However, the techno-functional properties of butter were mainly driven by cow breed. Compared to HF, butter from JFX cows was higher in firmness across 6 months of storage, higher melting and crystallization parameters, associated with higher short-chain FA and saturated FA, and lower monounsaturated FA levels. JFX butter showed more yellowness (b*), associated with increased ß-carotene levels. The butter of PRG JFX group exhibited the highest firmness, as well as the highest melting and crystallization parameters, which were associated with the highest levels of saturated FA, compared to the rest of the groups, indicating breed by diet interaction. From an aroma point of view, this group demonstrated the least "buttery" and most "green" aroma.
Finally, Chapter 7 summarized the major findings, scientific and industrial impacts and future considerations arising from the studies presented in this thesis. Overall, the findings presented in this thesis demonstrate that cow breed, diet and breed by diet interactions should be considered to target specific nutritional, techno-functional or organoleptic properties of milk, and high-fat dairy products such as whipping cream and butter.
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Keywords
Multispecies swards , Perennial ryegrass , Jersey-Holstein Friesian , Holstein Friesian , Milk composition , Butter , UHT-treated whipping cream , Fatty acid profile , Raman spectroscopy , Pasture diets , Dairy lipids , Cow breed , Prediction models
Citation
Kostovska, R. 2025. Impact of cow pasture diet and breed on the fat fraction of milk and dairy products in seasonal, spring-calving dairy production system. PhD Thesis, University College Cork.