Effects of a potato pulp silage supplement on the composition of milk fatty acids when fed to grazing dairy cows

This study was completed to determine the effects of potato pulp silage (PPS) as a diet supplement on the composition of milk fatty acids in grazing dairy cows in comparison to a barley grain supplement. Eight late lactation Holstein dairy cows were fed grazing based diets supplemented with 150 g/kg of PPS (‘PPS’) as a substitute for barley (‘barley’), and grazed on 4.3 ha swards, mainly containing orchard grass, for 56 days. Total dry matter (DM) and pasture DM intake and milk yields, as well as milk composition, did not differ between treatments. The linolenic acid intake did not differ (329 g/day vs. 323 g/day DM). The trans11C18:1vaccenic acid (VA) concentration in blood was higher in cows fed PPS (2.4 g/100 g FA) compared to those fed barley (1.9 g/100 g FA). There were no differences between treatments in the cis9trans11conjugated linoleic acid (CLA) concentration in blood. The short-chain and medium-chain fatty acids in milk also did not differ between treatments. The VA concentration in milk was increased in cows fed PPS (2.32 g/100 g FA) compared to those fed barley (1.84 g/100 g FA), and CLA was higher in cows fed PPS (1.25 g/100 g FA) than those fed barley (0.95 g/100 g FA). Milk CLA concentration was positively correlated to blood VA concentration. Results suggest that an increase in milk CLA concentration is related to an increase of the VA concentration in blood by Δ9-desaturase in mammary glands in the PPS fed compared to barley fed groups.