Digestion kinetics of ryegrass
A.V. CHAVES, G.C. WAGHORN, I.M. BROOKES AND D. HEDDERLEY
AgResearch, Grasslands Research Centre, Private Bag 11008,
Palmerston North, New Zealand
NZSAP 2002 Abstract No. 40
Proceedings of the New Zealand Society of Animal Production 62:
157-162
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.
Keywords: NZSAPAB;
ryegrass; forage maturity; digestion kinetics; in sacco;
in vitro; dairy cows
Last Updated 30/07/2002
