Changes in nutritive value and herbage yield during extended growth intervals in grass-legume mixtures: effects of species, maturity at harvest, and relationships between productivity and components of feed quality

There is a lack of information on the effects of companion species in grass-legume mixtures on herbage yield and quality changes during prolonged growth. Such information is relevant for harvest planning and estimation of consequences for feeding value of conserved feed when harvesting is delayed. Perennial ryegrass was sown with each of four legumes: red clover, white clover, lucerne and birdsfoot trefoil, and white clover was sown with hybrid ryegrass, meadow fescue and timothy. Effects of species composition on herbage yield, contents of N, neutral detergent fibre (NDF), acid detergent fibre (ADF) and lignin, ash and invitro organic matter digestibility (IVOMD) were studied in entire herbage and in component species during 2years in a small-plot cutting trial in Denmark. In May and August, the dynamic development of components of feed value and their interrelationships were investigated by sampling at optimum harvest date (i.e., normal practice)+/- 1week (t=-1 to t=+1). Herbage digestibility and contents of N and ash decreased while those of fibre compounds increased during the 2weeks from t=-1 to t=1 in all species. In May, contents of ADF and lignin increased at a faster rate in legumes than in grasses; in August, NDF and ADF increased most quickly in legumes. Generally, N contents and IVOMD declined at similar rates in grasses and legumes, but, within each group, differences in yield and quality development occurred among species. The relationship between weekly growth rate and change in quality parameters differed among species and functional groups, i.e., grasses and legumes. Results are discussed in the context of quantifying the impact of delaying the harvest date of grass-legume mixtures and relationships between productivity and components of feed quality.