The investigation of factors affecting milk fat production in dairy cows under pasture-based management systems
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Date
2024
Authors
Heffernan, Christopher
Journal Title
Journal ISSN
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Publisher
University College Cork
Published Version
Abstract
This thesis aimed to investigate factors affecting milk fat production in dairy cows in pasture-based production systems, with particular attention to the seasonal variability in milk fat concentration. Significant reductions in milk fat concentration are observed annually during late spring to early summer in pasture-based systems, posing considerable concern for the industry due to its economic consequences. However, our understanding of the factors associated with reduced milk fat concentration during this high-risk period of April to June is limited. Chapter 1 reviews the literature on milk fat synthesis and the possible factors associated with milk fat concentration. In Chapter 2, the effect of herbage mass on pasture nutritive value was investigated across the high-risk period. Although fatty acid (FA) concentration was greater for lower herbage mass swards, there was no effect of herbage mass on neutral detergent fibre (aNDFom) concentration. Overall, sufficient aNDFom concentrations to maintain milk fat production were achieved and pasture FA concentrations were moderate. Chapter 3 examined the effect of concentrate supplementation level and type on milk fat concentration in grazing dairy cows during the high-risk period. While no effect of concentrate supplement level or type on milk fat concentration was observed, increasing concentrate supplementation levels increased milk fat yield. Increasing concentrate NDF concentration with sodium hydroxide-treated straw had no effect on milk fat production while supplementation with a concentrate containing a blend of palmitic and oleic acids increased milk production. In Chapter 4, the effect of FA supplementation on milk fat production was further examined in genetically diverse grazing dairy cows during the high-risk period. Compared with a non-fat supplemented control, supplementation with 97% palmitic acid increased milk fat concentration but did not affect milk fat yield. In contrast, offering a FA blend containing 58% palmitic acid and 28% oleic acid had no effect on milk fat concentration, but tended to increase milk fat yield. Animal genetic group significantly affected milk fat production, with purebred Jersey cows producing the greatest milk fat concentration, while high economic breeding index (EBI) Holstein-Friesian achieved the greatest milk fat yield. Chapter 5 examined the relationship between nutritional and non-nutritional factors and bulk tank milk fat concentration on commercial grazing dairy farms. A predictive model was developed to estimate herd-level milk fat concentration and identified grazing rotation and the herd’s milk fat % predicted transmitting ability (PTA) as predictive factors associated with 73% of the observed variation in bulk tank milk fat concentration.
Overall, this research investigated a number of factors currently suggested to be involved in the reduction of milk fat concentration in pasture-based systems. There were no clear causative relationships determined between the pasture nutritive value parameters measured, or the concentrate supplementation levels investigated, and milk fat concentration. While FA supplementation did increase milk fat concentration, the economic viability of this strategy needs further attention. Genetic selection for milk fat % PTA was effective at increasing overall milk fat concentration; however, this is a longer-term solution. Future genetic investigations should explore the pattern of milk fat concentration as breeding for milk fat % PTA will increase the annual average milk fat concentration but might not capitalise on alleviating the consistent annual reduction in milk fat concentration during the late spring to early summer period.
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Keywords
Dairy cow , Milk fat production , Grazing , Seasonality , Palmitic acid , Oleic acid , Concentrate supplementation , Pasture fatty acid composition , Pasture aNDFom composition , Herbage mass , Holstein , Jersey , Milk fat concentration , Milk fat depression , Low milk fat syndrome , Milk fatty acids , Commerical dairy farms
Citation
Heffernan, C. 2024. The investigation of factors affecting milk fat production in dairy cows under pasture-based management systems. PhD Thesis, University College Cork.