Considerations for dairy cow nutrition in pasture-based systems.

Pasture-based dairy systems offer a sustainable and cost-effective approach to milk production, particularly in temperate regions. This review synthesizes current knowledge on the nutritional profile of pastures and the nutritional management of grazing dairy cows, emphasizing the unique challenges and opportunities associated with using nonpasture feeds (i.e., grains, coproducts, or conserved forages: commonly referred to as supplements) to fill pasture deficits or increase milk production. Well-managed fresh pasture is a high-quality feed capable of supporting moderate milk production; it supplies an excellent profile of metabolizable AA and highly and rapidly digestible fiber. Its nutritional profile fluctuates, however, with regrowth stage and season, making precise diet management impractical. Our current understanding suggests that supplementary feeding (1) should first be employed to address deficits in ME during periods of low pasture growth; (2) at >30% of DMI can lead to nutrient imbalances, particularly in MP and AA; and (3) can reduce pasture utilization and farm profitability. There is no evidence to support individualized feeding strategies. Further research is required to understand the situations in which supplementary fat or crude protein and AA will increase milk production and to help better parameterize models for use with pasture-based systems.