Effect of grain supplementation and the provision of chemical or physical fibre on marginal milk production responses of cows grazing perennial ryegrass pastures
Authors: Wales W. J. , Williams Y. J. , Doyle P. T. 
Published: September 2002

An experiment was undertaken to establish the marginal milk production
response from cereal grain supplementation by dairy cows grazing irrigated
perennial pastures in spring and whether the addition of a hay supplement
would improve that response. Cows were offered perennial ryegrass
(Lolium perenne L.)–white clover
(Trifolium repensL.) pasture at allowances (measured to
ground level) of 20 or 40 kg dry matter (DM)/cow.day. Additional cows
offered the low allowance were also offered supplements of pasture hay as a
cube or pellet (2.5 kg DM/day), cereal grain as a pellet (5.0 kg
DM/day) or cereal grain plus pasture hay (7.5 kg DM/day) as a pellet
(1.75:1 DM basis) or cube (1.97:1 DM basis). The 7 treatments were replicated
3 times, and 63 cows were used (3 cows/treatment).
The in vitro DM digestibility, crude protein and neutral
detergent fibre (NDF) concentration of the barley and perennial pasture hay
were 863 and 563 g/kg DM, 131 and 92 g/kg DM, and 182 and 666 g/kg
DM, respectively. Cows from all treatments consumed herbage with an
in vitro DM digestibility of 833 g/kg DM, crude
protein content of 214 g/kg DM and NDF concentration of 457 g/kg DM
compared with the pregrazed herbage on offer of 771, 174 and 527 g/kg DM,
respectively. The mean pregrazing herbage mass of 4.13 t DM/ha consisted
of perennial ryegrass (507 g/kg DM), white clover (188 g/kg DM), weeds
(194 g/kg DM) and dead material (111 g/kg DM).
Without supplements, cows consumed 11.2 kg DM/day at the low pasture
allowance and 15.6 kg DM/day at the high allowance. Herbage intake did not
decline to a large degree when barley was included in the diet, where a
substitution rate of 0.2 kg reduction in pasture DM/kg DM cereal grain
supplement was measured. The NDF concentration of the diet consumed was lowest
(P< 0.05) for the grain pellet treatment (370 g
NDF/kg DM) and highest (P&lt;0.05) for the fibre
pellet (493 g NDF/kg DM) and the fibre cube (507 g NDF/kg DM)
treatments. Fat-corrected milk yield increased
(P<0.05)) from 20.1 to 24.5 kg/cow.day when
cows consumed 4.5 kg DM cereal grain/day with a marginal milk response of
1.0 kg 4% fat-corrected milk/kg DM concentrate supplement.
Supplementation with grain or hay had no significant effect (P>0.05) on
milk fat, protein or lactose concentrations. The cows offered the high
allowance spent more (P<0.05) time grazing than
those offered the low allowance, but there were no significant differences in
rumination time. Cows spent more time ruminating when consuming the grain
&plus; fibre cube compared with the other supplement treatments, which
were lower (P<0.05) and similar. Cows offered
pasture at the low allowance ruminated the least. The rumen pH was not
different between treatments and averaged 5.9. The ratio of acetate plus
butyrate: propionate was not different between treatments and averaged 4.3.
This study has shown that feeding cereal grain to cows grazing pastures high
in perennial ryegrass resulted in acceptable marginal milk responses of 1 kg
milk/kg DM of cereal grain in spring because of sufficient NDF in the
diet. As there was adequate NDF in the diet, further supplements with pasture
hay as cubes or pellets had no effect on marginal milk responses .