3.2.1 Survey of key farm data
3.2.1.1 Average farm
Descriptive statistical information for the selected farm category in New Zealand was collated every 5 years from 1980 to 2011. The data used were obtained from Beef + Lamb New Zealand by email
correspondence (www.beeflambnz.com) and from a publication Supplement to the New Zealand Sheep
and Beef Farm Survey (SNZSBFS, 1983, 1984, 1988). The data collated were mainly for factors related
to feed demand and supply of the farming system. The data included farm size (total and effective area), hay or silage area, animal number (sheep and cattle), reproductive performance (lambing and calving percentages), and chemical inputs (lime and fertiliser application).
3.2.1.2 Case farms
To evaluate data at the farm level, similar types of data were collated for the 1980–81/1985–86 and
2010–11 production periods, for the three case-study farms (A, B, and C), also hill country farms
belonging to the same farm category (e.g., Figure 3.1, Farm A), located at –40.3462 (latitude)/175.6178
(longitude), –40.6527/176.128 and –40.8422/175.618, southeast North Island, New Zealand,
respectively. The information was obtained from farm diaries for Farms A and B and from the annual
feed budget prepared by the farm manager in 2009–2011, Parker and Lowe (1980/1981), and Parker
(1986) for Farm C. All farms practiced rotational grazing, except during lambing (spring) where the
ewes and lambs were set stocked, had detailed records spanning the 25–30-year study period suitable
for this study, and (at the time of this study) were performing above the national average in terms of effective farm area and animal stock units per hectare. Farms A and B have been operated by the current farmers over the past 25 and 30 years, respectively. Farm C (Riverside Farm) has been operated by Massey University since 1979 (Parker and Lowe, 1980/81).
Figure 3.1 A view of Farm A, illustrating slope and pasture type typical of the farm and the region generally.
3.2.2 Farm system performance analyses
3.2.2.1 Feed demand and consumption modelling
The initial plan was to model the feed demand and consumption of the system every 5 years since 1980. However, since data were not available for some years, the time intervals studied were re-selected
based on the years for which data were available. For the average farm, the periods studied were 1980–
81, 1985–86, 1992–93, 1999–00, 2003–04, and 2010–11. For Farm A, the periods studied were 1985–
86, 1999–00, 2003–04, and 2010–11. The periods studied for Farm B were the same as those studied
for Farm A, with the addition of 1980–81, 1992–93, and 2011–12. The latter were included to verify the
trends in 2010–11. For Farm C, the periods were 1980–81, 1985–86, and 2010–11.
(a) Acquisition of animal data
For the average farm, the numbers of animals by type and age class were obtained from the Supplement to the New Zealand Sheep and Beef Farm Survey (SNZSBFS, 1983, 1984, 1988) and the New Zealand
Sheep and Beef Farm Survey (NZSBFS, 1988–2003) for the production periods 1980–81, 1985–86,
1992–93, and 1999–2000. Since that information was no longer published after 2002, the data were
obtained for 2003–04 and 2010–11, the numbers of animals by type and age class in 2002–03, 2003–04,
2009–10, and 2010–11 were calculated from the annual animal “stock units” reported by Beef + Lamb
New Zealand (2012) for these periods, taking data for the previous year as “opening stock”, and data for the subsequent year as “closing stock”. For Farms A and B, the data were obtained from farm
diaries. For Farm C, the data were obtained from Parker and Lowe (1980/81), Parker (1986), and from
the annual feed budgets prepared by the farm manager in 2009–2011.
(b) Modelling of animal metabolic energy requirements
The animal metabolic energy requirements were calculated on a monthly basis from the animal monthly liveweight data, which were obtained from previous reports on New Zealand farming (Appendix 3.1) and from the farm diaries of Farms A, B, and C. The calculation utilised equations published by Nicol and Brookes (2007) (Appendix 3.2); the methodology was reviewed in Chapter 2 (Section 2.2). The requirements were calculated using a standard Microsoft®Excel template adapted from one used by Massey University over the last 15 years (e.g., Matthew et al., 2010) and that indicated by Webby and Bywater (2007). The calculation was slightly adjusted in two respects. First, Nicol and Brookes (2007) propose that if the metabolisable energy (ME) content of the diet is above (or below) 10.5 MJ per kg
dry matter (DM) (11 MJ ME kg DM–1 for lactating ewes), a flat rate of 7% (or 10% for lactating ewes) of body maintenance energy should be deducted from (or added to) the total energy requirements. In this study, the deduction (or addition) in body maintenance energy requirement with increasing (or
decreasing) herbage ME from the herbage ME threshold (10.5 or 11 MJ ME kg DM–1) was not applied
as a sudden increment at a threshold value of ME as proposed by Nicol and Brookes (2007), but the rate
(%) was instead calculated as a gradual transition using the formula: (|Monthly herbage ME – Herbage
ME threshold|) ÷ herbage ME threshold u 100. Second, the energy cost of weight gain for adult steers
and bulls was taken to be 70 MJ ME per kg liveweight gain rather than 55 MJ ME per kg liveweight gain, used by Nicol and Brookes (2007), and energy recovered during weight loss of sheep was decreased by 5 MJ ME per kg liveweight to 20 MJ ME per kg liveweight. These adjustments were made to take account of anecdotal comments from New Zealand farmers suggesting that modification to published coefficients would better reflect farmer experience of feed consumption during paddock grazing events.
(c) Energy values assumed for pasture when converting energy requirements to feed demand
The conversion of energy requirements to feed demands was based on the ME content of browntop/
ryegrass-clover (Agrostis capillaris L./Lolium perenne L.-Trifolium spp.) pasture grown on New
Zealand farms. For periods before 2005–06, the ME of herbage on Tuapaka Farm reported by McRae
(1987) was used (Appendix 3.3). For periods after 2005–06, the ME of herbage reported by Machado et
al. (2005) on the same farm was used (Appendix 3.3). These data were used because (a) the ME of herbage was historically rarely measured on New Zealand farms and thus, using known information from a farm of similar pasture type the nearest farm is an option for forecasting feed demand (Waghorn, 2007; Webby and Bywater, 2007) and (b) the farmers of Farms A and B believed that the nutritive
value of herbage on their farms had improved since 1980–81/1985–86. For calculations for the average
farm, the ME of herbage for finishing cattle was lowered, compared to the value used for herbage eaten by sheep. As cattle typically follow the sheep mob in the rotation, the herbage grazed by the cattle will tend to have lower ME content than that grazed by the sheep (Morris and Smeaton, 2009). The reduction in the ME of herbage grazed by cattle compared with that grazed by sheep was based on percentages extracted from Figure 1.2 in Morris and Smeaton (2009). For Farm A, the ME of herbage
for finishing cattle was assumed to be the same as that for sheep, because this farm did not operate a rotation that prioritised sheep. For Farms B and C, the ME of herbage consumed by cattle and sheep was assumed to be the same as that of the average farm.
(d) Comparison of model output with commercial software Farmax®Lite
For benchmarking purposes, the feed demand estimates for Farm C in 1980–81 and in 2010–11 were
calculated using Farmax®Lite (www.farmax.co.nz), a commercial feed budgeting software package widely used in New Zealand, and compared with those obtained from the Microsoft®Excel spreadsheet model developed in this study. The calculations using Farmax®Lite incorporated farm system details, seasonal change in stock numbers (sold stock was set to random in terms of liveweight following the practice on the farm) and animal liveweight, hay and crop area, and farm size of Farm C.
3.2.2.2 Herbage accumulation modelling
The herbage accumulation on the respective farms was modelled using a software package named GROW, for the same periods as those used in the feed demand modelling described above. GROW was specifically designed for the New Zealand farm environment. A description and limited validation of the GROW model has been reported by Butler et al. (1990). The model uses rainfall, temperature, and soil fertility data as the main inputs, and other parameters relevant to soil water storage as minor inputs. In this study, the default set-up of the model was used, except for herbage composition (ryegrass-white- clover-browntop), soil fertility (Olsen P = 10), soil type (moderate clay loam), and cutting rotation (28 days). For the national farm average, mean temperature and rainfall data for central and southern parts of North Island were obtained from NIWA (2013) (www.niwa.co.nz). For Farms A and B, the data were obtained from farm diaries. For Farm C, the data were obtained from Radcliffe (1975), Parker and
Lowe (1980/81), Thompson (1982), Parker (1986) and from NIWA (2013) for 2010–11 data.
3.2.2.3 Feed conversion efficiency
The FCEs of the systems were estimated for the average and case farms during 1980–81 and 2010–11
production periods. FCE was expressed as amount of feed required (kg DM) per product (kg carcass of sheep + cattle, kg sheep carcass, lamb weight and number of lambs weaned, kg cattle carcass, and calf weight and number of calves weaned). Feed demand information was obtained as described in Section 3.2.2.1. The annual carcass weight data were obtained from the Supplement to the New Zealand Sheep
and Beef Farm Survey (SNZSBFS, 1983, 1984) and from Beef + Lamb New Zealand (2013). Additional carcass weight data were obtained from farm diaries, Parker and Lowe (1980/81), and Parker (1986). The liveweight to carcass weight conversion rates were 40% and 51% for sheep and
cattle, respectively (Farmer A, pers. comm.).