The present study sought to quantify the differences between maize-based (MS) and grass-silage-based (GS) diets in terms of their effect on the milk yield, milk fatty acid composition and antioxidant capacity in dairy ewes, and to test the hypothesis that it is possible to improve yield, fatty acid (FA) composition and antioxidant capacity by supplementing diet with camelina seed (Cs). Experimental diets consisted of a 2 x 2 factorial arrangement of type of silage (GS vs. MS) and camelina seed (−Cs vs. +Cs). Feeding the MS diets increased net energy for lactation (NEL) intake, raw milk yield and fat, protein and lactose yields. Feeding +Cs increased energy corrected milk (ECM), milk fat content and fat yield. Maize silage consumption is associated with an increased proportion of hypercholesterolemic fatty acids (HFA) and a higher value of the atherogenicity index. However, an MS diet led to an increased share of t11-C18:1 and c9,t11-conjugated linoleic acid (CLA) in milk. Milk FA profile in ewes fed GS diet was of higher quality for human beings owing to higher concentrations of α-linolenic acid and a lower content of HFA. Supplementing with camelina seed resulted in a higher concentration of t11-C18:1, c9,t11-CLA and C18:3n-3 in milk fat. The trolox equivalent antioxidant capacity (TEAC) value of milk was higher in milk from MS-fed ewes compared with that of their counterparts fed GS. Dietary supplementation with camelina seed increased the oxidative stability of milk samples. These results suggest that grass-silage-based diet supplemented with camelina seed results in milk of better quality for human consumption.