Recent evidence from observational studies and controlled clinical trials indicates that milk fat, although predominantly saturated, has neutral or positive effects on cardiometabolic health. Such benefits have been attributed to the complex and unique chemical nature of milk fat, which contains several compounds potentially beneficial to health, such as butyric acid (C4:0), vaccenic acid ( trans-11 C18:1), rumenic acid ( cis--9, trans-11 CLA), oleic acid ( cis-9 C18:1), α-linolenic acid (C18:3 n-3) and some odd– and branched-chain fatty acids (e.g. C15:0). In particular, most of the rumenic and oleic acids secreted in milk are synthesized in the mammary gland by the action of the stearoyl-CoA desaturase-1 (SCD1) enzyme through the introduction of a double bond at carbon 9 in its precursors ( trans-11 C18:1 and C18:0, respectively), and the ratios between their products and substrates (referred to as desaturase indices) are commonly used as indicators of the activity of this enzyme in the mammary gland. A significant proportion of the phenotypic variation in milk fatty acid profile has been attributed to the occurrence of polymorphisms in the SCD1 gene in taurine breeds, but there have been no such studies with zebu breeds. Given the importance of the Gir breed and its crossbreds for milk production in Brazil, this project aimed to: 1) Estimate the phenotypic variation in milk fatty acid profile, determined by gas chromatography; 2) Investigate, by means of an association study, the influence of polymorphisms in the SCD1 gene (identified by 'target sequencing') on this trait; and 3) Predict the functional impact of the genetic variants using bioinformatics tools. Individual milk and blood samples were collected from 312 Gir cows between 30 and 120 days of lactation, distributed in 10 herds located in the states of Minas Gerais, São Paulo, Espírito Santo, Paraíba and Rio Grande do Norte. A smaller individual variability was observed for the SCD18 index in relation to the other desaturase indices, and this response is consistent among the different published studies, suggesting that the activity of SCD1 on C18:0 is more tightly regulated than for the other substrates of this enzyme in the mammary gland. Fourteen variants of SCD1 were identified, six of which have not yet been reported in the literature. All animals were homozygous for the main polymorphism described in taurine breeds (A293V), which results in the substitution of an alanine for a valine in the protein. On the other hand, all genotypes (AA, GA and GG) were detected for the second SNP (single nucleotide polymorphism) of the A293V variant (i.e. G>A substitution at the third base of the codon), with evidence of functional effects of this mutation, consistent with the association observed between this SNP and the proportions of oleic acid and rumenic acid in milk fat, and with their respective desaturase indices (i.e. cis-9 C18:1/C18:0 and cis-9, trans-11 CLA/ trans-11 C18:1). In addition, another SNP (rs523411937) found in the 3'UTR region of the SCD1 gene was also associated with the proportions of certain fatty acids and desaturase indices in milk fat. Finally, a new variant identified in this study (N244D) was predicted to affect protein function, which deserves investigation in future studies. The results of this study showed that, as observed in taurine breeds, there is considerable phenotypic variation in milk fatty acid profile of Gir cows, with some of the SCD1 variants identified in this study showing potential for use in future breeding programs of this breed aiming at increasing the nutritional value of milk.