ABSTRACT. Mastitis remains a major cattle disease with great global economic implications. Various approaches are currently employed in attempts to improve understanding of mastitis resistance and develop phenotypic markers for use in breeding programs (e.g., somatic cell score), including QTL discovery, wide-genome association studies, and identification of candidate genes related to immune function. This study evaluated three single nucleotide polymorphisms contained in Toll-like receptor 4 (TLR4) and lactoferrin (LF) genes associated with mastitis traits: TLR4 P-226, TLR4 2021, and LF P-28. Genotyping was performed by restriction fragment length polymorphism-polymerase chain reaction (PCR) and high-resolution melting quantitative PCR from genomic DNA of four dairy cattle breeds (Holstein, Jersey, Montbeliarde, and Overo Colorado) previously classified as healthy, with clinical or with subclinical mastitis. The high-resolution melting quantitative PCR allowed genotyping of each locus and resulted in allele frequencies indicating that all loci were in Hardy-Weinberg equilibrium. The TT genotype of TLR4 2021 was significantly associated with the healthy condition, but no associations with somatic cell score were evident. Further studies are therefore necessary in order Single nucleotide polymorphisms and mastitis in dairy cattle to confirm the results of this investigation.

ABSTRACT. Milk fat composition is important to consumer health. During the last decade, some fatty acids (FA) have received attention because of their functional and beneficial effects on human health. The milk FA profile is affected by both diet and genetics. Differences in milk fat composition are based on biochemical pathways, and candidate genes have been proposed to explain FA profile variation. Here, the association between DGAT1 K232A, SCD1 A293V, and LEPR T945M markers with milk fat composition in southern Chile was evaluated. We selected five herds of Holstein-Friesian, Jersey, Frisón Negro, Montbeliarde, and Overo Colorado cows (pasture-grazed) that received strategic supplementation with concentrates and conserved forages. We genotyped the SNPs and calculated allele frequencies and Hardy-Weinberg equilibrium. Milk fat composition was determined for individual milk samples over a year, and associations between genotypes and milk composition were studied. The most frequent variants for DGAT1, SCD1, and LEPR polymorphisms were GC/GC, C, and C, respectively. The DGAT1 GC/GC allele was associated with lower milk fat and protein content, lower saturated fatty acid levels, and higher polyunsaturated FA (PUFA), n-3 and n-6 FA, and a linolenic acid to cholesterolemic FA ratios, which implied a healthier FA profile. The SCD1 CC genotype was associated with a low cholesterolemic FA content, a high ratio of linolenic acid to cholesterolemic FA, and lower conjugated-linolenic acid and PUFA content. These results suggest the possible modulation of milk fat profiles, using specific genotypes, to improve the nutritional quality of dairy products.