Milk fatty acid and protein profiles of late-lactation dairy cows as affected by time of allocation of a fresh strip of ryegrass-based pasture

Eighty late-lactation dairy cows were used to examine the effects of allocating a new strip of a ryegrass (Lolium perenne L.)-based sward in the morning (AM) or in the afternoon (PM) on milk fatty acid (FA) and protein profiles. Total polyunsaturated FA (PUFA) in milk were greater from cows on AM herbage, whereas total saturated and monounsaturated FA (MUFA) were similar. The relative contribution of saturated FA was greater in morning-collected milk, whereas the contribution of MUFA, PUFA and total FA were greater in afternoon-collected milk. Time of allocation only affected the milk protein component α-casein, which was greater in milk from cows on PM herbage, affecting in turn the casein:whey ratio. A greater concentration of precursor FA in AM herbage resulted in a greater concentration of beneficial FA in milk, compared with cows on PM herbage. These benefits were fully captured in milk collected following the allocation period.