Effects of feeding additional pasture hay in autumn to dairy cows grazing irrigated perennial ryegrass-white clover pasture and supplemented with barley grain
Authors: Wales W. J. , Dellow D. W. , Doyle P. T. , Egan A. R. 
Published: September 2002

Two experiments were undertaken to investigate
responses by dairy cows grazing irrigated perennial pastures in autumn to
supplementation with barley grain and pasture hay. Cows in late lactation were
offered limited amounts of perennial ryegrass–white clover pasture at 26
kg DM/cow. day. Supplements were offered as nil or 6.0 kg DM/cow.day
plus perennial pasture hay at 0, 0.5, 1.2, 2.0 or 3.0 kg DM/cow. day in a
replicated experiment with 6 treatments using 36 cows (3 cows/treatment
replication). The second experiment, which was conducted concurrently with
experiment 1, measured aspects of rumen function and blood parameters in 3
groups of 3 rumen fistulated lactating cows grazing at the same herbage
allowance and supplemented with barley (6.0 kg DM/cow. day) and 0, 1.0 or
3.0 kg DM of pasture hay daily.
The in vitro DM digestibility and crude protein and
neutral detergent fibre content of the barley and perennial pasture hay was
863 and 640 g/kg DM, 134 and 87 g/kg DM and 192 and 615 g/kg DM,
respectively. In experiment 1, the cows from all treatments consumed herbage
(mean s.d.) with an in vitro DM digestibility of 811
21.8 g/kg DM, crude protein content of 233 26.0 g/kg DM and neutral
detergent fibre content of 404 39.4 g/kg DM compared with the pregrazed
herbage on offer of 710, 152 and 526 g/kg DM, respectively.
The mean pregrazing herbage mass of 3.75 t DM/ha in experiment 1 consisted
of perennial ryegrass (580 g/kg DM), white clover (100 g/kg DM), weeds
(110 g/kg DM) and dead material (210 g/kg DM). Without supplements,
cows consumed 10.0 kg DM/day of this pasture with a neutral detergent
fibre intake of 4.43 kg/day. The herbage grazed in experiment 2 was
similar. Herbage intake did not decline to a large degree when barley was
included in the diet indicating a very low substitution rate under the
prevailing conditions where herbage allowance was only 26 kg DM/cow. day.
Inclusion of hay progressively decreased (P<0.05)
herbage intake, with substitution averaging 1.2 kg DM of herbage/kg DM of
hay. Total DM intakes (15.5 kg DM/cow. day) were similar for the barley
and the barley plus hay treatments up to 2.0 kg DM hay/cow. day; total DM
intake was higher (P<0.05) for the 3.0 kg hay
treatment. Milk production increased (P<0.05) with
grain and hay supplementation, the marginal response being 0.8–1.0 kg
milk/kg DM supplement, however, there was no significant difference
between the 5 supplemented treatments. Supplementation with hay had no
significant effect (P>0.05) on milk fat or milk
protein contents which averaged 44.6 and 35.2 g/kg milk, respectively.
The ratio of acetate + butyrate:propionate was 4.1:1 when cows consumed
6.0 kg barley, which was around the critical ratio of 4:1 for milk fat of 40
g/kg. Increasing the amount of hay in the diet did not alter this ratio.
Because of the high levels of substitution of hay for pasture, changes in
neutral detergent fibre intake were small between supplemented treatments. The
rumen pH, ammonia-N concentration and volatile fatty acid concentration were
relatively stable during the day because of a relatively slow rate of eating
(1.5 kg DM/h) and long rumination time (about 6.8 h/day). Ruminal pH
was rarely below 6.0, even when barley was given alone, suggesting that fibre
digestion was not compromised. Additional fibre as supplemental hay to cows in
late lactation grazing irrigated pasture did not improve milk production when
the neutral detergent fibre content of the diet was above an average of 336
g/kg DM. Use of hay as a means of providing additional fibre could reduce
herbage utilisation.