RESUMEN
This study was performed with the main objective of evaluating the effect of the combination of pelleting and monensin on fatty acids (FA) composition, the concentration of total polyphenols and flavonoids, and the oxidative stability of milk in cows fed a concentrate containing soybean seeds. Eight Holstein multiparous cows were distributed in a replicated Latin square design. The four supplement treatments consisted of the combination of two factors (pelleting and monensin) and one concentrate as follows: (1) unpelleted concentrate with no monensin (CO); (2) pelleted concentrate with no monensin (PE); (3) unpelleted concentrate with 96 mg of monensin/kg of dry matter, DM (MO); and (4) pelleted concentrate with 96 mg of monensin/kg of DM (PM). There was no interaction between pelleting and monensin for milk production and concentration of milk protein, lactose, total polyphenols, flavonoids, conjugated dienes (CD), and reducing power. Fat and total solids concentration in milk were decreased when cows were fed pelleted (PE and PM) concentrates. Feeding cows with PE and PM concentrates increased the CD concentration in milk. Regarding milk FA concentration, there was no difference among treatments for total saturated, monounsaturated, and polyunsaturated FA. The most prominent result was that pelleting increased the milk concentration of omega-3 FA. Altogether, the present study suggests that the pelleting process can improve the milk fat quality by increasing the omega-3 FA, while the combination of pelleting and monensin in the diet of grazing dairy cows fed soybean-based concentrate adds no further improvements to FA profiles and oxidative stability of milk.