a b s t r a c t
Dairy systems in southern Australia rely on grazed feed from pasture to supply between 50% and 70% of
total herd feed requirements on an annual basis. However, the dominant pasture type in the region,
which is based on perennial ryegrass (Lolium perenne), commonly results in feed deficits in summer
which must be filled with supplements purchased off-farm, and feed surpluses in spring which must
be conserved. Both of these strictures impose costs on farm businesses. It is likely, therefore, that additional
grazeable feed available to dairy herds in southern Australia may have different economic value
when interactions between season, stocking rate, calving date, and locality are taken into account. The
analysis reported in this paper aimed to estimate, using the farm systems simulation model UDDER,
the effect of these interactions on the efficiency with which extra feed can be converted to extra milk production,
and therefore the possible gross economic value of the additional feed.
‘Base’ farm simulations for ‘average’ and ‘top 10%’ farms (ranked according to farm profitability) in two
localities (Terang: average annual rainfall 796 mm, 8 month growing season; and Ellinbank: average
annual rainfall 1085 mm, 9–10 month growing season) were created to mimic the physical production
and profitability of these farms as seen in regional farm benchmark datasets. These simulations were
then altered to add the equivalent of 10% of the total annual herbage accumulation used in the Base simulation
either on a pro-rata basis all year round, or in autumn only, in winter only, in spring only, or in
summer only. The additional feed amounted to 620 and 780 kg DM/ha for Terang average and top 10%
farms respectively, and 735 and 905 kg DM/ha for Ellinbank average and top 10% farms respectively.
The management policies used in the Base simulations were then adjusted to harvest as much of the
extra feed as possible, either by direct grazing or through silage conservation, while keeping the key system
state indicators of cow condition score and average farm pasture cover within the limits known to
result in long-term sustainable production.
The efficiency with which extra feed was utilised was greatest in summer in all scenarios (80–100% of
the extra feed supplied was harvested, all by direct grazing). This translated into consistently high gross
economic returns of between $0.26 and $0.34 per kg DM of extra feed added to the model. Utilisation efficiency
was lower in all other seasons and/or required marked increases in silage conservation, both of
which resulted in lower gross economic returns per kg DM of additional feed. The impact of interactions
between locality, season, stocking rate (higher in top 10% farm simulations than average farm simulations)
and calving date (earlier at Terang than at Ellinbank) were clearly captured in the model. These interactions
have very large effects on the profitability of growing extra feed at different times of the year. Agronomic
research for the southern Australia dairy industry should focus on low-cost ways for supplying
additional grazeable feed in summer, since current forage species options for this time of year are limited