P. ITTI
Introduction
Materials and methods
Results
Conclusion
References
The Gambian cattle population totals approximately 300,000 N'Dama head and its level of production is currently considered satisfactory. However, due to an annual 2.6 to 3% increase in human population, the demand for beef and milk is rising. Since optimal stocking rates are thought to have been reached, increasing the productivity per head is required. A simulation model of the national cattle herd production is used to observe and analyze the responses to strategic nutritional interventions over a ten-year period.
The analysis was carried out using a modified version of the microcomputer herd model, written in LOTUS 1.2.3 and developed at ILCA (von Kaufmann et al., 1987). The modifications were made in order to consider only the production data of the Gambian national herd and the projections of these simulated over a period of ten years. The main results were:
1. the total herd size evolution expressed as numbers of TLU, since this is the determining factor when looking at the stocking rates; and2. the mean annual increase in production output during the ten-year period in terms of a) meat production, b) milk production and c) number of oxen. Traction being a major production output in The Gambia, it was assumed that the oxen used for traction should also record an increase in numbers to sustain growth, particularly in the crop-production sector.
To simulate the possible developments of cattle production, estimates of base production parameters were needed. Table 1 presents those used for this study. They were pooled together from the four reports referred to below.
Table 1. Base production parameters of the national cattle herd in The Gambia.
|
|
Herd structure, weights and culling rates |
||
|
Numbers of animals |
Weights (kg) |
Culling rates (%) |
|
|
Breeding cows |
112,760 |
210 |
1.0 |
|
Calves, 0-1 years |
51,623 |
40 |
0.0 |
|
Calves, 1-2 years |
53,990 |
100 |
3.0 |
|
3 year heifers |
13,096 |
130 |
16.0 |
|
4 year heifers |
14,500 |
187 |
10.2 |
|
Oxen |
17,672 |
265 |
10.0 |
|
3 year males |
11,000 |
150 |
11.0 |
|
4 year males |
12,000 |
208 |
15.0 |
|
5 year males |
4,000 |
240 |
40.0 |
|
6 year males |
1,500 |
240 |
60.0 |
|
7 year males |
800 |
240 |
70.0 |
|
8 year males |
600 |
240 |
80.0 |
|
9 year males |
|
240 |
90.0 |
|
10 year males |
|
240 |
100.0 |
|
Total |
293,541 |
|
|
|
Reproductive performance |
Herd survival rates |
||
|
Calving rate: |
50% |
Calves, 0-1 years |
80% |
|
Age at first calving: |
4 years |
Calves, 1-2 years |
90% |
|
|
|
Cattle, > 2 years |
95% |
|
Cow lactation yield |
Killing out |
|
|
|
300 l |
52% |
|
|
Sources: The African Development Fund, 1982.
ITC, 1987a.
ITC, 1987b.
Riley, J. 1987.
The increasing culling rates of the males from five to ten years of age were introduced in order to have a regular culling of old males. The cow culling rate was very low to ensure that, despite the poor reproductive performance and survival rates, sufficient replacements were available. Once more precise data on mortalities are collected, a higher cow culling rate may be possible.
Strategic nutritional intervention trials are being carried out by the ITC and preliminary results have been reported. (Riley et al., see article 38 of these Proceedings). These, together with estimates of possible productivity improvements due to supplementary feeding of crop by-products, have been used to predict improvements during a ten-year period. The predicted changes are presented in Table 2.
Table 2. Livestock productivity changes due to intervention.
|
Years |
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
10 |
|
Annual calving rate (%) |
50 |
52 |
54 |
56 |
58 |
60 |
62 |
64 |
66 |
66 |
|
Calf survival, 0-1 yrs (%) |
80 |
80 |
81 |
82 |
82 |
83 |
83 |
84 |
84 |
85 |
|
Calf survival, 1-2 yrs (%) |
90 |
90 |
91 |
91 |
91 |
92 |
92 |
92 |
93 |
93 |
|
Adult survival >2 yrs (%) |
95 |
95 |
95 |
95 |
96 |
96 |
96 |
97 |
97 |
97 |
|
Cow lactation yield (1) |
300 |
302 |
303 |
305 |
306 |
308 |
309 |
311 |
313 |
315 |
Results with present production parameters
Using the base production parameters, two computer runs were performed to look at the future outcome with the present productivity level remaining constant throughout the 10 years. Table 3 gives the output results. Further details are given in Appendix 1.
Table 3. Output increase after a ten-year simulation, given the present productivity level.
|
1) Herd-size increase in numbers of TLU: +39.7% over 10 years | ||||
|
2) |
Mean Annual increase in production output: | |||
|
|
a) |
Meat production |
: |
+3.2% |
|
|
b) |
Milk production |
: |
+3.6% |
|
|
c) |
Number of oxen |
: |
+3.9% |
These data show that although the increase in production would take place at a rhythm higher than that of the increase in the human population, this would result from a 39.7% increase in the national herd size. This is not likely as stocking rates are already said to be optimal.
A second run was performed with the same base parameters but using the model's option for the automatic culling rule. This stabilizes the numbers of breeding cows at its initial level and is intended to be used in cases such as this where higher stocking rates are not acceptable and grazing land cannot be expanded.
Table 4. Output increase after a ten-year simulation given the present productivity level but with a stabilized population of breeding cows.
|
1) |
Herd size increase in numbers of TLU: +2.3% over 10 years | |||
|
2) |
Mean increase in production output: | |||
|
|
a) |
Meat production |
: |
+0.6% |
|
|
b) |
Milk production |
: |
+0.0% |
|
|
c) |
Number of oxen |
: |
+2.4% |
The results presented in Table 4 show that stabilizing the number of breeding females is almost sufficient to stabilize the overall herd structure and size (see Appendix 2). The meat and milk production increase on the other hand was below the expected 2.6 to 3% increase in demand, This model gave priority to an increase in the oxen population since the development of cattle production should not be detrimental to the crop sector where the oxen are needed.
The results of the two first runs indicate that the productivity level in The Gambia is not high enough to sustain a 2.6 to 3% production increase. At the moment increases of that size can only be attained through an increase in herd size.
Results with improved production parameters due to nutritional interventions
Two subsequent runs were performed with the improvements in productivity resulting from the supplementary feeding.
In order to stabilize the herd size, additional measures were required since the automatic culling alone was not sufficient. In the third run, all the numbers of females above three years and those of males above five years of age were stabilized at their initial level, while the number of breeding females had to be reduced below its initial level (see Appendix 3). The results in Table 5 show a stabilized herd size coupled with a good increase in meat production and in the numbers of oxen; the shortfall was the milk production since a 1.9% increase would not meet predicted demand.
Table 5. Output increase after a ten-year simulation with improved productivity resulting from nutritional interventions.
|
1) |
Herd-size increase, TLU: -0.6% over 10 years | |||
|
2) |
Mean increase in annual production output: | |||
|
|
a) |
Meat production |
: |
+4.1% |
|
|
b) |
Milk production |
: |
+1.9% |
|
|
c) |
Number of oxen |
: |
+4.0% |
As an alternative, a fourth run was performed with a smaller reduction in the number of breeding cows. The objective was to achieve a 3% increase in milk production (Appendix 4; Table 6). Because of this change, the introduction of higher culling rates of three- to four-year-old heifers and the two- to four-year-old males coupled with a reduction in the numbers of oxen were necessary in order to maintain a constant herd size. The results in Table 6 show a satisfactory increase in meat and milk production, but the numbers of oxen increased by only 1.5%. It could, however, be assumed that part of the increase required in work could be covered by a larger draught oxen population and by a more efficient use of the work oxen, horses and donkeys. In addition improved techniques such as the single ox plough and the draught collar instead of the traditional yoke could be used. Draught cows could also contribute to the additional traction requirements. Matthewman (1987) reports that in Sine Saloum, Senegal, 27% of work animals are female.
Table 6. Output increase, with emphasis on milk production after a ten-year simulation improved productivity resulting from nutritional interventions.
|
1) |
Herd-size increase, TLU: +1.6% | |||
|
2) Mean increase in annual production output: | ||||
|
|
a) |
Meat production |
: |
+4.0% |
|
|
b) |
Milk production |
: |
+3.0% |
|
|
c) |
Number of oxen |
: |
+1.5% |
The results of the simulations indicate that with the present productivity level the cattle production output would not meet the demand resulting from a human population increase of 2.6 to 3% without prejudice to the environment through overstocking. With strategic nutritional interventions designed to increase reproductive performance, survival rates and milk yield' annual output increases of meat, milk and draught power would be possible which would satisfy the growing human requirements even with no increase in the size of the national herd.
African Development Fund. 1982. Appraisal Report, Livestock Development Project, Republic of The Gambia.
International Trypanotolerance Centre. 1987a. Progress report of the research project on N'Dama production.
International Trypanotolerance Centre. 1987b. Research project on the productivity of N'Dama cattle in Senegambia. Second Annual Report, 1986-1987.
Matthewman, R.W. 1987. Role and potential of draught cows in tropical farming systems: a review. Trop. Anim. Hlth. Prod. 19: 215-222.
Riley, J.A. 1987. Nutrition project of the EEC funded research programme at the International Trypanotolerance Centre, The Gambia. Final report of consultant nutritionist.
Von Kaufmann, R., J. McIntire, P. Itty and Edjigayehu Seyoum, 1987. User's Manual for ILCA's Microcomputer Herd Model. Addis Ababa: ILCA.
Appendix 1. Projected output results over 10 years given the present productivity level
Appendix 2. Projected output results over 10 years given the present productivity results but with a stabilized population of breeding cows.
Appendix 3. Projected output results over 10 years with improved productivity resulting from nutritional interventions.
Appendix 2. Projected output results over 10 years with improved productivity resulting from nutritional interventions with emphasis on milk.
