Genetic variation of milk fatty acid composition between and within dairy cattle breeds

<strong>Abstract</strong> Maurice – Van Eijndhoven, M.H.T. (2014). Genetic variation of milk fatty acid composition between and within dairy cattle breeds. PhD thesis, Wageningen University, the Netherlands Fat is one of the main components in bovine milk and comprises a large number of individual fatty acids (FA). The composition of FA in milk varies considerably due to differences in the genetics and nutrition of cows and an increasing interest in the possibilities for modifying FA composition can be noticed nowadays. In this thesis two fields of interest were combined, namely: production of milk with specific milk fat composition and conservation of native cattle breeds. Therewith, the overall objective of this thesis was to investigate the variability of detailed milk FA composition between and within different dairy cattle breeds, including the mainstream Holstein Friesian (HF) and Jersey, and the native dual purpose breeds Meuse-Rhine-Yssel (MRY), Groningen White Headed (GWH) and Dutch Friesian (DF) in the Netherlands. For this study the accuracy of mid-infrared (MIR) spectrometry was evaluated for predicting FA composition in different breeds. Differences of milk FA composition within and between breeds were investigated using MIR and Gas Chromatography (GC) information. Finally, similarities in genomic variation associated with detailed milk fat composition between the mainstream HF breed and native dual purpose breeds were studied. Results show that MIR is an accurate method for predicting FA composition among different breeds and countries. Evaluating the FA composition in different breeds, differences were found in milk FA composition among herds using different cattle breeds in the Netherlands, based on detailed milk FA measurements using GC. Evaluating the FA composition in milk between and within breeds using a large dataset that included MIR spectra of milk from cows from a range of farms using one or more breeds, in general, only minor breed differences in FA composition were found and HF showed more genetic variation in FA composition compared to MRY. Furthermore, differences were detected between the native breeds MRY, DF and GWH in genomic variations of regions that are associated with FA composition in HF, while most variation in these main regions was clearly observed in HF. Overall, it was concluded that no large differences existed in milk FA composition among the native Dutch dual purpose breeds and the mainstream HF breed. It is suggested, however, that selecting specific FA composition differences in farms using different breeds in the Netherlands can attribute to modifying the FA composition in bovine milk production.