Replacing cereals with dehydrated citrus pulp in a soybean oil supplemented diet increases vaccenic and rumenic acids in ewe milk

This study evaluates the effect of the replacement of cereals by dried citrus pulp (DCP) in diets supplemented with 5% of soybean oil, on ewe milk yield and composition, including milk fatty acid (FA). Four Serra da Estrela multiparous ewes in the second month of lactation were used in a double 2×2 Latin square design. Ewes were individually penned and milked twice a day with an 8-h interval. Each experimental period included 14d of diet adaptation followed by 5d of measurements and sampling. The 2diets included on dry matter basis 450g/kg of corn silage and 550g/kg of either a soybean oil-supplemented concentrate meal containing barley and maize (cereal) or dried citrus pulp (DCP; citrus). Feed was offered ad libitum, considering 10% of orts, and intake was measured daily. Milk yield was higher and dry matter intake tended to be higher with the citrus diet. Milk composition and technological properties for cheese production were not affected by treatments, except for lactose, which was lower with the citrus diet. Replacement of cereals by DCP resulted in a 3-percentage-point decrease of both 18:0 and cis-9–18:1 that were mostly compensated by the 4.19- and 1.68-percentage-point increases of trans-11–18:1 and cis-9,trans-11–18:2, respectively. The intake of C18 FA tended to increase with the citrus diet compared with the cereal diet, but the apparent transfer of 18:2n-6 and of 18:3n-3 did not differ between diets. The milk output of C18 FA increased with the citrus compared with the cereal diet, mostly due to the increase of trans-11–18:1 and cis-9,trans-11–18:2 because the daily milk output of 18:0, trans-10–18:1, cis-9–18:1, 18:2n-6 and 18:3n-3 did not differ between diets. Replacing cereals with DCP in an oil-supplemented diet resulted in a selective increase of trans-11–18:1 and cis-9,trans-11–18:2 in milk, with no major effect on other biohydrogenation intermediates.