Milk yield and milk composition characteristics of grazing and all-silage dairy systems

摘要

With the objective of evaluating the variability in dairy cows' milk yield, milk composition and milk fatty acids (FA) profile when offering diets of varying degrees of intensification, 24 Holstein-Friesian dairy cows were randomly assigned to four feeding groups of contrasting diet composition for 12 weeks after peak milk yield. Two groups had access to a perennial ryegrass sward, either continuously during 24 h (Tl) or between morning and evening milkings (T2), and two groups (T3 and T4) were keptindoors throughout the experiment, having ad libitum access to total mixed rations (TMR), which differed in the composition of the silages (grass and maize or maize alone) and in concentrate proportion. Tl and T2were supplemented, with 2 kg cow'1 d~(-1)of concentrate dry matter (DM) and with lOkgDM cow~(-1) d~(-1) of a TMR based on maize silage and concentrates; respectively. Milk yield increased from 31.4kgd~(-1) in Tl to 37.8 kg d~(-1) in T4 with moderate changes in milk components. Compared with all-silage, high-concentrate diets, milk from grazing-based systems showed a less-saturated FA profile, a higher content in the beneficial FA c9tll-CLA, tl l-Cl&A and C18:3n3 and a lower omega-6 to omega-3 ratio.