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Research
results (primarily from Ireland) on dairy cow
herbage intakes with and without concentrate
supplementation are summarised in the Table. The
average intake values on grass alone range from
10.9 to 20.7 kg dry matter (DM) per day with the
majority of results falling between 12 and 17 kg
DM per day. Surprisingly, grass intakes in many
recent studies are similar to intakes recorded in
the eighties (with much lower genetic merit cows).
As cow genetic merit is very much a relative term,
to put some of the results into perspective, the
current national RBI is around 105. A number of
things such as, time of year, lactation stage, cow
genetic merit, cow age profile, grass allowance,
grass quality and whether the intakes obtained
were for grazed or zero-grazed animals need to be
considered when interpreting the results in the
Tables.
In
a detailed study, McGilloway (unpublished)
measured herbage intake of grazing dairy cows over
two consecutive years (1992 and 1993) in
Moorepark. Pastures were grazed to either 4cm
(severe grazing), 6cm (optimum grazing) or 8cm
(under grazing). This study had individual intake
points over the entire grazing season for each
year. Results showed that for each of the
treatments, grass intake was HIGHLY VARIABLE over
the grazing season. For the three treatments
combined, the average grass DM intakes in 1992, at
the first, fourth, seventh and ninth (final)
grazing cycles were approximately 14.7, 12.2, 13.7
and 14.3 kg respectively. Corresponding intakes
for the 6cm post grazing sward height treatment
(which is well established as the optimum for
grassland management - see later on) were
approximately 15.7, 12.4, 13.0 and 14.7kg. In
1993, the average DM intakes for the three
treatments combined at grazing cycles 1, 2, 3, 6
and 9 were approximately 13.6, 16.1, 14.2, 14.8
and 13.1kg respectively while corresponding
intakes for the 6cm post grazing height treatment
were approximately 13.8, 15.6, 13.3, 14.6 and
12.5kg. These two detailed experiments demonstrate
that the average grass DM intake of a dairy cow
under ideal grazing management conditions ranges
from 12.0 to 16.5 kg across the grazing season.
This
range in grass DM intake is CONSISTENT with values
obtained from nearly all published Moorepark
experiments (Table 1) carried out at various times
of the year, from the 1980’s right up to the
present day, with cows under optimum grazing
management (Stakelum 1986a, 1986b, 1986c; Stakelum
and Dillon, 1988, 1989a and 1989b; Dillon et al.,
1997; Maher et al., 1997) and also with
zero-grazed cows (Stakelum and Morgan, 1983;
Stakelum and Connolly, 1987; Keady and Murphy,
1993; O’Mara et al., 1997), as well as being
consistent with research data from Northern
Ireland (Cushnahan and Gordon, 1993; Cushnahan and
Mayne, 1994; Cushnahan et al., 1995; Sayers and
Mayne, 1998) and elsewhere (See Table 2). The fact
that these published grass intake figures under
Irish conditions, are available almost annually
for well over a decade, thus including good and
bad years for grass performance, demonstrates
realistically what’s actually happening and/or
possible at Irish farm level.
To
say "average cow intake of X kg are/or can be
achieved" can be misleading. Does it mean
intake for the whole grazing season or just when
grazing conditions are ideal? Does it mean herd
intakes which include primiparous cows or just
multiparous cows? etc. For example, it must be
noted that the "widely cited", highest
average reported grass intake figures of 18.6 to
20.7 kg DM per day obtained with high genetic
merit cows (Buckley et al., 1998) were: |
