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Increasing the number of grazing days achieved by dairy cowsAuthor(s): E. Kennedy, J. Curran, J.P. Murphy and M. O'DonovanSource: Irish Journal of Agricultural and Food Research, Vol. 48, No. 2 (2009), p. 261Published by: TEAGASC-Agriculture and Food Development AuthorityStable URL: http://www.jstor.org/stable/20720372 .
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Irish Journal of Agricultural and Food Research 48: 261, 2009
Increasing the number of grazing days achieved by dairy cows
E. Kennedy, J. Curran, J.P. Murphy and M. O'Donovan
Teagasc, Dairy Production Research Centre, Moorepark, Fermoy, Co. Cork, Ireland
Extending the grazing season has positive implications for profit margins, as grazed grass is the cheapest feed
available. Two of the biggest limitations when extending the grazing season are poor soil conditions and wet
weather. Allowing animals restricted access to pasture may be a method of achieving an increased number
of grazing days (Chilibroste et al, 2007). The objective of this study was to examine the effect of restricting
pasture access time on dry matter intake (DMI), grazing behaviour and milk production.
Fifty-two (20 primiparous and 32 pluriparous) Holstein-Friesian spring calving dairy cows (mean calving date 31 January) were balanced for lactation number (2.4; s.d. 1.43), milk yield (24.5 (s.d. 4.53) kg), body
weight (509, (s.d. 69.5) kg) and body condition score (3.31, s.d. 0.331) in a randomised block design with 4 treatments. The study was conducted from 25 February to 25 March, 2008. The four treatments were: full
time access to pasture (22H; control); 4.5 h pasture access after both milkings (2 x 4.5H); 3 h pasture access
after both milkings (2 x 3H); 3 h pasture access after both milkings plus silage supplementation (3 kg of dry matter (DM) per cow) by night (2 x 3HS). Cows on all treatments were offered a daily herbage DM (above 4
cm) allowance of 15 kg cow-1 day-1 and supplemented with concentrate (3 kg DM per cow per day). Treatment
groups grazed separate farmlets for the duration of the study so that effects on subsequent grass re-growth could be established. Pre- and post-grazing sward heights were measured daily. Milk yield was recorded daily,
milk composition, bodyweight (BW) and body condition score (BCS) were measured weekly. Dry matter
intake was measured during the third week of the study using the n-alkane technique. Grazing behaviour was
recorded using IGER grazing recorders. All variables were analysed using mixed model procedures.
Pre-grazing herbage DM mass was 1739 (s.e. 128.4) kg/ha for all treatments. Silage supplementation increased (+0.7 cm) post-grazing sward height compared to all other treatments (4.1 cm). Re-growth (DM)
was reduced by 20% (250 kg/ha) when paddocks became poached under fulltime grazing compared to pad docks where restricted access to pasture was involved.
There were no differences among treatments for most milk production variables. Supplementing cows with
silage reduced (P < 0.05) milk protein concentration (32.1 g/kg) compared to the 22H treatment (33.7 g/kg). Cows on 2 x 3HS treatment had a higher (P < 0.001) final BW (508 vs 488, 481 and 479 kg for 22H, 2 x 3H and 2 x 4.5H, respectively) but there was no difference in BCS among treatments. The 2 x 3H treatment
had greatest grazing efficiency as they grazed for 98% of their time at pasture compared to the 22H animals
(37%). Silage supplementation reduced grazing time (297 min) in comparison to the 2 x 3H treatment (353
min).
Restricting access to pasture is a method of increasing the number of days at pasture during wet weather
while simultaneously reducing paddock damage. However, cows should not be supplemented with silage as it
reduces grazing efficiency and milk protein concentration compared to the control treatment.
References
Chilibroste, R, Soca, R, Mattiauda, D.A., Bentancur, O. and Robinson, RH. 2007. Australian Journal of
Experimental Agriculture 47: 1075-1084.
261
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