Transcript No Slide Title

Nitrogen balances for three strains of dairy cows and contrasting
intensive grassland systems
W. Ryan1,2, D. Hennessy1, J. J. Murphy1, T. M. Boland2 and L. Shallloo1,
1Animal and Grassland Research & Innovation Centre, Teagasc, Moorepark, Fermoy, Co. Cork. Ireland
2School of Agriculture, Food Science and Veterinary Medicine, University College Dublin. Ireland
Introduction
•Grass based milk production systems in Ireland and other temperate climates have a competitive advantage over confined
systems due to the use of grass as a low cost feed source
•Grass based systems rely on inputs of N fertiliser and concentrate to ensure adequate feed supply for milk production
•N use efficiency is a key driver of environmental and economical sustainable, however, N use efficiency within animal
production systems is low
•Factors which influence N use efficiency of individual animals include genetic strain and feeding system
Objective
•To develop, evaluate and validate an annual dairy cow N balance model based on a range of Irish grass based dairy
production systems
Materials and Methods
• Three strains of Holstein-Friesian cows investigated - high-production North American (HP), high-durability North American
(HD) and New Zealand (NZ).
• Three pasture based production systems - Moorepark Blueprint system (MP), a high concentrate input system (HC) and a
high stocking rate system (HS).
• N inputs – fertiliser, feed, replacement animals
• N exports - milk, meat (calf and cull cow)
• Model outputs – N surplus and N se efficiency
• Two scenarios investigated:
•Scenario 1 (S1) examined N utilisation, N use efficiency and N losses of the contrasting dairy production systems,
excluding the N required to rear replacement animals for the production system (from birth to first calving)
•Scenario two (S2) was similar to S1 but included the N required to rear replacement animals for the production system
N Inputs
•Grazed
Grass
•Winter Feed
•Concentrate
N leached
or lost
through
gaseous
emissions
N
immobilised/
mineralisation
N
excreted
and
released
from soil
Recycled
N used for
grass
growth
Table 1. N input, N output, N surplus and N use efficiency of
three genetic strains of Holstein Friesian dairy cows managed
on three grass based systems, including the rearing of
replacement heifers (Scenario 2).
N Outputs
•Milk
•Meat
•Exported
feed
•Exported
slurry
Fig. 1 Schematic representation of the N balance model
Results
• Replacement rate for the NZ, HD and HP genetic strains
was 18%, 25% and 37%, respectively
• N input increased as replacement rate increased
• The N surplus per cow was greater for the HD and HP
-1
strains (141 and 157 kg N cow , respectively) than for the
-1
NZ strain (129 kg N cow ).
• The HP genetic strain was the most efficient of the three
strains in converting N to product (Table 1)
Production
system
Acknowledgement
This Project was funded by the Research Stimulus
Fund administered by the Department of Agriculture,
Fisheries and Food (RSF 05-201)
HC
NZ
MP
Strain of
HP HD
Holstein-Friesian
Total N input
197 179
169 206 190 169 198 182 171
Total N output
42
39
N surplus (kg N
-1
cow )
N use efficiency
(per cow)
156 139
41
HP HD NZ HP HD NZ
48
47
42
42
42
40
130 158 143 127 156 140 131
0.21 0.22 0.23 0.23 0.25 0.25 0.21 0.23 0.23
Fig. 1. N surplus (kg N/cow) for three genetic strains of
Holstein Friesian dairy cows managed on three grass based
systems in Scenario 1 (rearing of replacement heifers not
included) and Scenario 2 (including the rearing of replacement
heifers).
N surplus S1 (kg N/cow)
N surplus S2 (kg N/cow)
160
Conclusion
140
kg N/cow
•High replacement rate reduces N use efficiency
•HP animals had the least efficient N utilisation rates per cow
when the whole system including the rearing of replacement
animals was evaluated.
•The importance of including the rearing of replacement
heifers in the N balance
HS
120
100
80
HSHP
HSHD
HSNZ
HCHP
HCHD
Treatment
HCNZ
MPHP
MPHD
MPNZ