Abstract
The main objectives of this thesis were to investigate the effects of grazing severity,
treading damage, re-growth interval and pre-grazing herbage mass (HM) on sward and
animal performance in four experiments during 2009 and 2010 in Ireland. Experiment 1
investigated three post-grazing sward heights ranging from 3.6 to 4.9 cm during the
main grazing season. Herbage accumulated and harvested (11.3 and 11.2 t dry matter
(DM)/hectare (ha), respectively) were not significantly affected by grazing severity but
there were sward morphological and structural differences. Experiment 2 quantified the
effects of treading damage during two seasons, ranging from light to severe damage
(3.3 to 13.3-cm hoof-print depths, respectively). Treading damage in a perennial
ryegrass (PRG) sward on a well-drained soil did not reduce annual grass DM
production. Treading in a creeping bent-dominated sward on a poorly-drained soil
resulted in 14 to 51% reductions in cumulative yields depending on frequency and
season. Experiment 3 examined the effects of 2-, 3- or 4-week re-growth intervals on
herbage production, characteristics and tissue turnover of a PRG sward using marked
tillers (n = 240) under a cutting regime. Cumulative HMs were 6.7, 9.1 and 10.4
t DM/ha for the 2-, 3- and 4-week re-growth treatments, respectively. The number of
leaves appearing per tiller during the re-growth period was only optimum for the
4-week treatment. Experiment 4 also used marked tillers (n = 360) in a grazing dairy
cow experiment during the main grazing season under three target pre-grazing HMs
(945, 1,623 and 2,360 kg DM/ha >4 cm). The number of leaves appearing per tiller
during the re-growth period was 1.0, 1.9 and 2.4 for low (L), medium (M) or high (H)
pre-grazing HM treatments, respectively. Cows grazing L, M or H pre-grazing HM
produced 343, 342 and 330 kg milksolids, respectively. Low pre-grazing-HM cows
grazed for 90 min/day more than M and H pre-grazing-HM cows but there was no
difference in individual intake (16.0 and 15.8 kg DM/cow/day in June and August,
respectively). Post-grazing sward height, treading damage, re-growth interval and pregrazing
HM can have a significant impact on the sward and on animal performance. The
imposition of best management practice leads to a more effective conversion of grass
into milk.
Date
2013
Rights
The Author
Publisher
Massey University
Description
Ch. 7. published as: Tuñon, G., Lopez-Villalobos, N., Kemp, P.D., Kennedy, E, Hennessy, D.,
& O'Donavan, M. (2011). Effect of pre-grazing herbage mass on grazing behaviour, grass dry
matter intake and milk production of dairy cows. Proceedings of the New Zealand Society
of Animal Production, 71, 28-32.