Effect of

Simple Summary Growth hormone (GH) participates in the regulation of lactation and lipid metabolism. Milk traits and fatty acid composition were investigated in Modicana cows, in relation to the genetic polymorphism at GH locus p.L127V and its interaction with the feeding system. It has been compared 8 hours of grazing without concentrate (EX), versus 2 h of grazing with concentrate (SI). The frequencies of LL, LV and VV genotypes were, respectively, 0.64, 0.34, 0.02. The GH polymorphism and its interaction with feeding system did not influence milk yield and gross composition. LL cows showed higher levels of total unsaturated and monounsaturated fatty acids, thus suggesting a potential role of the GH polymorphism on improving the healthy quality of milk. A higher level of 18:1 in the LL cows was evident only in the extensive system. The lower energy input in the extensive system, compared to the semi-intensive system, could justify this result. Abstract Growth hormone participates in the regulation of lactation and lipid metabolism. A trial study was conducted to evaluate the effects of genetic polymorphism at GH p.L127V and its interaction with feeding system (extensive, EX; semi-intensive, SI) on milk traits and fatty acids composition in Modicana cows. In the semi-intensive farm (SI) diet consisted of hay, concentrate and 2 h of grazing. In the extensive farm (EX) feeding consisted in 8 h of grazing and hay. The frequencies of LL, LV and VV genotypes were, respectively: 0.64, 0.34, 0.02. GH polymorphism and its interaction with feeding system did not influence milk yield and composition. Cows carrying LL genotype produced milk with lower 6:0 and 8:0 and higher 16:1 c9 and 18:1 c9, total UFA and total MUFA. Feeding significantly affected fatty acids: in EX cows lower SFA and higher PUFA and UFA were found, compared to SI cows. The lower, more favorable atherogenic index of milk from EX system was coherent with the improved healthy characteristics of milk from animals fed almost exclusively on pasture. A significant interaction genotype x feeding system was evident for 18:1, higher in the LL cows only in the EX system, but not in the SI system.