Polymorphisms at Candidate Genes for Fat Content and Fatty Acids Composition: Effects on Sheep Milk Production and Fatty Acid Profile Using Two Dietary Supplementations

The fat component of sheep milk exhibits significant variability. While nutrition is widely acknowledged as the main factor affecting fat yield and fatty acid profile in ruminants' milk, genetic factors also contribute to this variation at breed and individual levels. This study aimed to examine the impact of genotypes and feed integration on milk quality in Valle del Belice sheep. To achieve this aim, two polymorphic lipogenic genes (DGAT1 and SCD) and the impact of two dietary supplementations (carob pulp and barley grain) were investigated. Carob pulp, a local agro-industrial by-product rich in carbohydrates and tannins, was selected due to its potential to positively affect ruminant metabolism, suggesting a viable and sustainable alternative for ruminant feeding from economic and environmental perspectives. The genotype at the DGAT1 locus significantly affected both the milk urea content and milk fatty acid composition. The carob pulp supplementation, compared to barley, increased the fat percentage but worsened the milk fatty acid profile in terms of healthy properties. The interaction between genotypes and diet was not evident.Abstract: The nutritional value of sheep's milk and its derivatives is influenced by the lipid fraction, which is affected by diet and genetics. This study aimed to explore the genetic variations in the DGAT1 and SCD genes and assessed the impact of the DGAT1 genotype on milk quality in Valle del Belice sheep, considering diet supplementation with carob pulp and barley grain. Among the potentially polymorphic sites, only DGAT1 g.127 C > A and SCD g.87 C > A showed variability. The DGAT1 genotype did not significantly impact milk yield and composition, except for higher urea content in the CA genotypes than in the CC ones. Carob pulp increased the milk fat content compared to barley grain. Genetic variation in DGAT1 was associated with changes in the milk fatty acid profile; specifically, the CA genotype exhibited higher levels of short-chain fatty acids and lower levels of polyunsaturated fatty acids compared to the CC genotype. Carob pulp supplementation increased saturated fatty acids and reduced unsaturated fractions, leading to milk with higher atherogenic and thrombogenic indices. No significant interaction was found between genotype and diet. This study provides insights into the genetic and dietary factors influencing sheep's milk composition. Further research is needed to understand the impact of these genetic variations on milk production and composition, as well as to determine optimal levels of carob pulp for improving fat percentage and promoting sustainable sheep breeding practices.