Abstract

Changes in ryegrass maturation, with accompanying decreases in nutritive value and feed intake, have significant consequences for the dairy industry. Thus digestion kinetics of ryegrass were measured in samples differing in both physiological age (days after cutting) and calendar date to form a database that can be used as a guide to calculate the extent and type of supplement needed to match nutrient supply with requirements of grazing dairy cattle. Ryegrass pasture was mown on 21 August, 11 September, and 21 September and samples of approximately 2 kg were harvested from those dates at 7-14 day intervals for chemical analyses by cutting to 5 cm above soil level. These samples were used for in sacco and in vitro incubations to determine rate of digestion and proteolysis. The principal finding was a rapid decline in crude protein content from about 22.5% of DM harvested at 21 days to 7.2% for that harvested after 67 days. These changes were associated with increases in the neutral detergent fibre (NDF) fraction of the DM (42.1% to 56.3%) and in lignin concentration (2.49% to 3.07%). Changes were more rapid in late-cut than early cut forages. The principal consequences of increased maturity were slower degradation rates of DM (k= 0.067 to 0.038/hour) and CP (k= 0.122 to 0.052/hour) and less degradation of crude protein to ammonia. This data can be used in conjunction with dairy cow models (e.g., CNCPS) to predict animal performance.

AV, Chaves, GC Waghorn, IM Brookes, and D Hedderley

Proceedings of the New Zealand Society of Animal Production, Volume 62, Palmerston North, 157-162, 2002