An in sacco (nylon bag) technique was used to estimate
the degradability of dry matter (DM) and crude protein, and to estimate the
effective rumen degradability of protein (ERDP), for 3 irrigated clover
herbages. Pasture characteristics (nutritive values and leaf: stem ratios)
were also described, and relationships to ERDP established. The nutritive
value characteristics and degradabilities of white clover
(Trifolium repens L.), Persian clover
(Trifolium resupinatum L.), and subterranean clover
(Trifolium subterraneum L.) were also compared for
various regrowth periods (of 3, 4, 6, and 12 weeks). Nutritive value
characteristics of clover herbages varied from 9.9 to 11.9 MJ/kg DM for
metabolisable energy, 153 to 304 g/kg DM for crude protein, and 209 to 377
g/kg DM for neutral detergent fibre. The leaf: stem ratio correlated well
with the crude protein content of the clovers, with herbages consisting of
more leaf generally having superior crude protein content
(R2 = 0.64,
P < 0.001).
The effective rumen degradability of protein for clover herbages ranged from
60 g/kg DM for mature (12 week regrowth) subterranean clover to 195
g/kg DM for vegetative (3 weeks regrowth) Persian clover. For clover
herbages with a 3-week regrowth period, after initial cutting to 5 cm, and at
ruminal outflow rates of 0.08/h, the effective rumen degradability of
protein varied from 136 to 195 g/kg DM. A positive relationship between
crude protein and ERDP (R2
= 0.82) suggested that ERDP could be estimated for clover herbages that
have been previously assessed for crude protein content, obviating the need
for in sacco studies. Calculated degradabilities were
lower for all clovers when higher ruminal outflow rates were assumed.
Using the metabolisable protein system, metabolisable protein supply and
metabolisable protein in excess of animal requirements were calculated.
Ruminal losses of nitrogen were also estimated for cows consuming white clover
of varying regrowth periods in both early and late lactation. It was concluded
that metabolisable protein supply is unlikely to limit production in these
examples. At regrowth periods of 3 weeks, metabolisable protein contributions
from microbial and dietary sources were similar, and twice that required by
the animal. Ruminal losses of nitrogen were substantial and amounted to
66—23% of nitrogen intake. In the experiments reported here,
if all of the energy required to excrete excess protein (as urea) could
instead be used for the production of milk, cows may have produced
0.5mp;mdash;2.0 kg more milk per day. Such losses could potentially be
reduced if the protein content and/or degradabilities of clover herbages
were reduced, and/or energy rich supplements were offered.
Development of yield and nutritive value of timothy in primary growth and regrowth in northern growing conditions