Challenges in ration formulation in pasture-based milk production systems

Abstract

The profitability of temperate dairy systems in southern Australia and New Zealand is underpinned by the efficient use of the home-grown feed-base and purchased supplements. While there are well established principles on which to devise nutritionally balanced rations for ruminants, it is evident that in grazing systems the variable supply of nutrients from forage often results in suboptimal performance compared with predicted responses. This review discusses the key factors likely to directly affect responses to supplementation in grazing systems, namely pasture supply, nutritive characteristics and intake, feeding systems, substitution, associative effects and nutrient synchrony. Intake is the primary driver for metabolisable energy (ME) and nutrient supply and uncertainties on the actual ME and nutrients supplied by pasture will remain due to variability within and between pasture types and within paddocks. It is suggested that improvements in ration formulation will require a better understanding of the kinetics of intake and digestion within the rumen and of nutrients supplied to the tissues from grazed pasture with and without supplements. Research which clearly elucidates which mechanism or mechanisms determine substitution rates with concentrate and forage supplements would be valuable. Such knowledge could also be used to develop feeding strategies that result in a reduction in the degree of substitution and, in turn, lead to higher DM and ME intake compared with existing feeding practices. This in turn would lead to a better understanding of associative effects and nutrient synchrony with benefits in better design of rations and feed-use efficiency.