The stock unit system - fair treatment for the breeding cow?
H.K. Crawford, K.I. Lowe
Department of Agricultural and Horticultural Systems Management,
Massey University, Palmerston North, New Zealand.
Proceedings of the New Zealand Society of Animal Production 1994,
54: 319-322
The stock unit (SU) system has been widely used in conjunction with
gross margin (GM) and analysis to make recommendations to farm managers
on the comparative profitability of pastoral livestock systems. This information
can be misleading, particularly where beef breeding cow policies are being
compared with finishing cattle policies that involve high rates of liveweight
gain (e.g. bull beef production). To illustrate the deficiencies of the SU system
for standardising between different livestock enterprises, relative gross margins
per stock unit (RGM/SU) were derived for two case study farms in contrasting
environments. One property was located in the Manawatu region (Tuapaka),
the other at Port Waikato (Limestone Downs) in South Auckland. Using the
breeding cow as a base (=100), the RGM/SU at Limestone Downs for breeding
ewes, bull beef, steer finishing and once bred heifers were 70, 158, 74 and 121,
respectively. If these RGMIsu were expressed in terms of returns per kilogram
of pasture consumed ($/kg) the rankings, relative to breeding cows (=100),
were breeding ewes (51), bull beef (95), steer finishing (53) and once bred
heifers (106). Corresponding values for breeding ewes and bull beef at
Tuapaka were 59 and 65. Thus, the substitution rates between livestock
enterprises varied substantially depending on the method used to account for
differences in feed consumption. The implications of these findings for farm
management decision making are discussed.
Keywords: NZSAPAB;
Stock units; gross margins; breeding cows; relative gross margins.
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Last Updated 25-01-1997
