Good FMS assumed that pastures were assessed with 85 per cent accuracy. Surplus was taken when residuals were consistently greater than 1700kg DM/ha, with paddocks greater than 4000kg DM/ha harvested.
Poor FMS assumed little assessment of pre-grazing and hence poor feed allocation. Surplus was taken when residuals were consistently greater than 2000kg DM/ha, with paddocks greater than 4000kg DM/ha harvested.
Variation in pasture growth between paddocks was modelled using data from 26 paddocks on DairyNZ's Scott Farm, Hamilton, from June 1, 2011, to May 31, 2012, where growth rate differences of up to 30 per cent were observed between the highest and lowest producing paddocks.
A typical Waikato farm was simulated using NIWA weather data for three climate years. 2012/13 prices were used: $290/t DM for purchased silage; $270/t DM for PKE; $140/t DM for silage made from the milking platform; and a cost of $40/t DM for feeding supplements. The results come from modelling on a milk price of $3.65/kg MS. Modelling was also undertaken at a $5/kg MS price.
The results showed increasing annual pasture yields from poor to optimal FMS (Table 1). The higher pasture yield in the optimal scenario came from better control of average farm covers and post-grazing residuals in November to February, compared with the good and poor FMS ( Table 1).
Lower pasture covers in June-July and lower residuals in September resulted in approximately 0.5 t DM/ha more pasture yield in the good FMS, compared with poor. This is explained by the fact that more pasture is grown by keeping average pasture cover in the rapidly growing phase of the grass growth curve. It is achieved by having good post-grazing residuals (1500 to 1700kg DM/ha) and not allowing covers at the top end of the pasture wedge to get too high.
Regarding milk production, good FMS was predicted to increase milksolids production by around 70kg MS/ha. Both good and poor FMS had periods of under- and over-feeding, resulting in fluctuating intakes and milk production.
However, periods of under-feeding were more frequent and more severe in poor feed management, indicating that paddock selection and therefore pasture allowance was wrong more often. The occasional over-feeding in both good and poor scenarios came from inaccurate supplement feeding, which resulted in increased dry matter intake, but also wastage of pasture through substitution.
Operating profit
Milksolids production and cost of supplements were the main factors that influenced the operating profit predictions for the three scenarios. Profit was approximately $134/ha higher in the optimal than good FMS (Fig. 1), driven mainly by the latter's higher cost of supplements due to less pasture grown, less silage made and more PKE purchased (Table 1). The higher profit of approximately $199/ha of good compared with poor FMS was primarily due to the latter's lower milk production, the consequence of more frequent and more severe under-feeding of lactating cows. The operating profit of $199/ha was sensitive to milk price and changed to $292/ha at $5.
The potential benefit of $199/ha for good FMS should be moderated by approximately $23/ha/year to account for costs of weekly pasture assessments and pasture data evaluation to improve grazing management decisions. This adjustment results in a total increased operating profit of $176/ha at a $3.65/kg MS milk price. A similar adjustment for costs took the $5 milk price operating profit to $269/ha.
The results suggest that good feed management of pasture, when compared with poor, can increase operating profit by $176/ha at a milk price of $3.65. The quality of pasture mass estimates will vary depending on how these are conducted. However, this study does indicate that the costs associated with time and effort required for grazing management are small in comparison with potential gains in operating profit.
More information: dairynz.co.nz/grazing-management
- Modelling done by DairyNZ's Pierre Beukes, Sean McCarthy, Cathal Wims and Alvaro Romera
