System Interactions and the Relative Importance of System Parameters

Multifactor experimentation further demonstrated the importance of using a systems-thinking approach. In this research, it was found that while ewe size did have a considerable impact on feed conversion efficiency, the combined effect of lamb growth rate, lambing percentage and lamb carcass weight had a much greater impact. Therefore, similar to the conclusion made by Dickerson (1978), “body size per se is of little importance in determining feed conversion efficiency in animal meat production when compared with the functional output per unit of body size in reproduction, growth and body composition”. In other words, ewe size alone should not be the primary factor in considering the type of ewe. For example, a 60% increase in ewe weight (from 50 kg to 80 kg) can be compensated by about a 20% increase in lambing percentage (from 110% to about 133%) (see Table 7.9).

Although lamb growth did impact on feed conversion efficiency, fast growth rates will not make up for the inefficiencies associated with very low carcass weights. It is with higher carcass weight that the benefit of fast growth rate can be captured. However, in considering the combined effect of lamb growth rate and carcass weight, a factor of importance is the mature size of the lamb. In the model, it was assumed that post-weaning growth rate was constant. However, it is well known that, in reality, growth slows as lambs reach maturity (Fitzhugh, 1976; Owens et al., 1993). If ewe size

remains constant, increasing carcass weight will increase the weight for maturity relationship and therefore, higher carcass weights should result in slower growth as lambs near maturity.

The increasing importance of lamb growth rate when reproductive rates are higher is consistent with the conclusion of Large (1976, p. 54). As reproductive performance increases, the total energy requirement of lambs relative to the energy requirement from breeding ewes increases, and thus, fast lamb growth and a reduction in the maintenance energy cost of lambs(due to their early slaughter) will have a greater impact on system feed conversion efficiency. From these results, it is clear that in a flock situation, the effect of lamb growth rate on feed conversion efficiency should not be overemphasised, especially when reproductive performance is low.

A key insight is that the importance of system parameters depend on the system context and the performance levels of other system parameters.

7.9.5

Stocking Rate

From analysis of the results of the multifactor experimentation presented in this chapter, feed conversion efficiency was negatively correlated to ewe numbers at mating date (Figure 7.5). For example, from 214 observations, an increase of 100 ewes corresponded to an average reduction of 0.16 g carcass/MJME. Therefore, while individual livestock production parameters can have a positive correlation with feed conversion efficiency, across the range of parameters investigated, maximum feed conversion efficiency of livestock systems is unlikely to be achieved through maximum stocking rate (number of ewes per ha). This is explained in that the primary drivers of system feed conversion efficiency are parameters that reduce maternal feed overhead, most notably being lambing percentage and lamb carcass weight. These parameters effectively transfer the allocation of feed requirement from the ewe to the lamb and, within a fixed feed supply constraint, require ewe numbers to reduce. This general principle that lower stock numbers and higher animal performance will result in higher system feed conversion efficiency was also reported in dairy livestock systems by Jensen et al. (2005).

Figure 7.5 The relationship between the number of ewes at mating date and feed conversion efficiency (g carcass/MJME) under different scenario combinations of production parameters

7.10Summary of Key Findings

There are several ‘big picture messages’ which have emerged from this research. First, through the combined change to multiple livestock system production parameters, large improvements in system output and biological efficiency are possible, with the feed conversion efficiency of the maximum system scenario being greater than double that of the minimum system scenario. This suggests that farmers have considerable potential to improve the productive output from their farms irrespective of their capacity to influence feed supply. This also implies that, as an industry, there is considerable potential to increase total sheep meat production despite land use constraints and limited feed resources.

In relation to strategies for increasing feed conversion efficiency, a second key message is that factors that reduce maternal feed overheads per unit of output have the greatest impact on feed conversion efficiency. Also, factors that impact on the numerator in the meat output per feed input equation will have the greatest impact on feed conversion efficiency. All else remaining constant,

y = -0.0016x + 5.2049 R² = 0.5206 1.5 2.0 2.5 3.0 3.5 4.0 4.5 900 1,000 1,100 1,200 1,300 1,400 1,500 1,600 1,700 1,800 FC E (g carca ss /MJ ME )

Ewe numbers at mating date 1 2 3 4 5 1 2 3 4 5

Lambing % (lambs tailed/ewe mated) 170% 171% 110% 105% 120%

Pre-Wng LWG (g/day) 450 450 250 250 250

Post-Wng LWG (g/day) 200 200 200 100 100

Ewe Size (kg) 80 50 50 80 65

Lamb Carcass Weight (kg) 24 24 12 12 24

Hgt Lambing % (hgt lambs tailed/total hgt) 60% 121% 60% 0% 60%

Cull Age (years) 7.3 6.3 7.3 10.3 7.3

MA Ewe Mortality Rate (%) 3% 1% 3% 7% 3%

higher lambing percentages and target carcass weight will have a much greater effect on feed conversion efficiency in comparison to lamb growth rate.

A third key message is that, in most cases, simultaneous changes in individual livestock system parameters do not have a simple additive effect on feed conversion efficiency. For example, for lamb growth rate and lambing percentage the combined impact of these parameters was complementary with the effect of lamb growth rate on feed conversion efficiency increasing as lambing percentage increased. In contrast, the impact of pre-weaning and post-weaning lamb growth rate parameters had a less than additive impact on feed conversion efficiency. Understanding such system dynamics is therefore important in planning for efficient production systems.

A fourth key message is that there are many possible system combinations that result in similarly high feed conversion efficiency, i.e. there is more than one way for high system efficiency to be achieved. This means that if, for whatever reason, improvement in one particular production parameter cannot be achieved, this does not necessarily limit the potential of the system to achieve high production efficiency. Also, while the sheep livestock system is complex, through dynamic system interactions, it is possible to “design” a livestock system to both match closely with the feed supply profile and to be efficient at converting feed into meat carcass output.

Through simultaneous changes to system parameters, farmers can also have a very large amount of control on the seasonal profile of feed demand. There is no a priori reason why highly efficient livestock production systems are limited to a specific feed demand profile. Therefore, this suggests that through the implementation of the correct production strategies, high feed conversion efficiency can be achievable irrespective of the feed supply context.

An important caveat to the above comments is that these findings do not take into account any specifics about feed in different times of the year having a different cost. In the next chapter, the biological linear programming model is extended to illustrate how these factors can be incorporated within the modelling framework.