Available at: https://digitalcommons.calpoly.edu/theses/661
Date of Award
MS in Agriculture - Dairy Products Technology
The selection of dairy cattle is dictated by improvement of yield and composition of milk. Genotyping tests give breeders the opportunity to use previously unavailable information to increase the frequency of beneficial alleles in their herds. A QTL influencing milk yield and composition is located in the centromeric end of chromosome 14. The polymorphism being analyzed is a K232A substitution (lysine to alanine amino acid change) in exon VII of the diacylglycerol acyl transferase 1 (DGAT1) gene. DGAT1 is a key acyltranferase in triglyceride biosynthesis. DGAT1 encodes an enzyme which catalyzes the final step of mammalian triglyceride synthesis from carbohydrates. The K232A substitution in the DGAT1 gene has an effect on milk production traits by having a higher milk fat content. The two nucleotide polymorphisms in exon VII (aa to gc) give rise to an MwoI restriction fragment length polymorphism (RFLP) which is used to identify the three DGAT1 genotypes (AA, AG, GG). Research has shown that the genotype AA of the DGAT1 gene is associated with higher milk fat. Since the United States has been selecting for milk volume and protein, herds in the US should have a higher proportion of the G allele.
The objective of this study was to examine the association of DGAT1 genotypes with fat content, lipid profiles, citrate levels, and MFGM proteins in the Cal Poly Herd. Our results confirmed that allele A is correlated with higher average percent milk fat content in Cal Poly Holstein and Jersey cows and shows a link between genes and fat composition. The changes were also reflected in the variability of MFGM proteins and lipid profiles. No statistically significant results were seen in citrate levels. In addition to examining the correlation between genetic variants and milk composition, there was a desire to examine the DGAT1 expression in epithelial mammary cells. These live epithelial cells were obtained via the novel technique of magnetic separation, which had questionable results. Microscopic evidence shows binding has limited success, and the inconclusive correlation between DGAT1 genotype and gene expression could be due to either the small sample size or limited extraction of viable epithelial cells. Bovine genomic DNA has been successfully extracted from milk cells, and this technique was tested with the examination of cells in milk powder. This technique had great success and shows great promise for future research in determining point of origin.