- Trampling by small stock
|Last update: September 2, 2011 03:21:10 PM|
TRAMPLING BY SMALL STOCK
PW ROUX & PA SCHLEBUSCH
Grootfontein College of Agriculture Private Bag X529 Middelburg Cape 5900
Trampling effects of small stock on the soil and vegetation are well known. Its exertion is largely associated with the breed of animal, ranging habit, and physiographic factors. The results of trampling are often characteristic of a particular environment, for example the narrow footpaths in grassveld as opposed to the wider paths in karooveld.
The capacity of a grazing animal to inflict soil disturbance by trampling is primarily linked to distance walked per day, hoof pressure and length of stride. These factors are largely intrinsic to a particular breed of animal. The distance walked per animal per day is primarily governed by the daily fodder requirement of the animal and external factors such as the availability of fodder, the size of grazing area, and weather conditions.
Roux (1979) introduced a so-called relative trampling factor (RT-factor) and determined this for some breeds of small stock (Table 1). The higher the factor the greater the potential ability to disturb surfaces by trampling.
TABLE 1 - The relative trampling factor (RT-factor) of some small stock breeds
Standard sheep 1,00
Merino ewe 1,07
Merino wether 0,93
Dorper ewe 0,84
Angora doe 1,13
The R T -factor, per se, is of no significance until the animal begins to walk. If an animal with a low RT-factor walks appreciably more than one with a high factor such an animal could cause an overall greater amount of perturbation by trampling.
It therefore appears that the relative capacity of breeds, or types, to trample can be reflected by RT x D where RT = the relative trampling factor and D = average distance walked per day. RT x D can conveniently be expressed as a RTD-index relative to a hypothetical animal with an average walking distance of 10 km/day with an R T -factor of 1,00.
Distance walked for some small stock breeds was determined by Louw, Havenga and Hamersma (1948). Table 2 shows some of these results.
TABLE 2 - Average distances (km) walked per day by ewes of four breeds of sheep run together and separately on mixed Karoo veld (Louw, et al., 1948)
Breed All Breeds Together Separate
Blackhead Persian 4,94 4,93
*Dorset x Persian 4,76 5,10
Karakul 4,18 3,46
Merino 4,13 3,60
*Later to become the Dorper
These measurements were made by tracking the sheep visually and plotting their movement on a diagram of the particular grazing area. As a result of the considerable variation in distances walked per breed and between breeds per day and the small number of replicates, no statistical differences could be ascertained. Nevertheless Table 2 shows that appreciable differences probably do exist.
The principal small stock breeds on the extensive grazing lands in the Karoo Agricultural Region are Merino and Dorper sheep, and Angora and Boer goats. In order to determine average walking distances for some types of these breeds, use was made of an apparatus (Photograph 1) similar to that described and successfully employed by England (1954).
Merino wether fitted with distance meter
In the pilot experiment, reported here, the breeds and types (see Table 3) were fitted with the apparatus. In the determination of D, three animals per breed were released, to range together with a flock of the same breed, on mixed karoo vegetation on a triangular area of 31 ha. The vegetation was generally in a very dry condition and it is possible that walking distances were greater than average.
Trials per breed were concluded after a continuous period of three days. Distance readings were made daily at 10h30. These trials were conducted from July to mid-August. Results over this period could have been influenced by changes in weather and a decline in forage quality over time.
Louw, et al., (1948) pointed out that distance walked could be affected by day length as greater distances were recorded during summer.
The result of the trials is shown in Table 3. Distances walked by Angora kapaters and Boer goat ewes are included for comparison purposes. Till now no RT-factors have been determined for these types and use of estimates were made.
TABLE 3 - Average walking distance, D, per day for some small stock breeds and types on mixed karoo veld, showing RT-factors and RTD-indices (Figures within brackets are estimates)
Breed and Type D (km) R T-factor R T x D RTD
1. Merino wether 9,18 0,93 8,54 0,85
2. Merino ewe 5,96 1,07 6,38 0,64
3. Angora kapater 5,94 (1,20) (7,13) (0,71)
4. Dorper ewe 5,90 0,84 4,98 0,54
5. Boer goat ewe 5,70 (0,75) (4,27) (0,43)
6. Angora doe 3,57 1,13 4,03 0,40
7. Standard sheep 10,00 1,00 10,00 1,0
From Table 3 it is clear that appreciable differences exist between breeds and types.
It can also be seen that there is a considerable difference between the highest and lowest RTD-index. It is further clear that the Angora doe has the lowest RTD-index but the highest RT -factor. This shows that walking distance and trampling ability must be coupled in order to assess the potential of a breed to trample during the process of ranging. The ranking order for distances walked appear in column D in Table 3. The descending order for the RTD-index is Merino wether, Angora kapater, Merino ewe, Dorper ewe, Boer goat ewe and Angora doe. By comparing Merino and Dorper ewes (Tables 2 and 3) it can be seen that they have very similar walking distances under the particular circumstances. Table 4 provides an example of the daily variation in ranging per Merino ewe and among the ewes.
TABLE 4 - Distances walked (km) per day by three Merino ewes over three consecutive days
Ewe No. 1st day 2nd day 3rd day Av. km/day
A 4,81 5,86 4,91 5,19
B 7,90 4,75 4,87 5,84
C 5,44 6,63 8,48 6,85
Table 4 shows that the average ranging distances do not differ much but that individual variation can be quite large e.g. ewe B 1st to 2nd day, and ewe C 2nd to 3rd day. Similar variation was shown by the other breeds and types. In the trial the greatest distance ranged per day by any animal was 12,29 km by a Merino wether, and least, 2,36 km by an Angora goat doe. The greatest total distance travelled over three days was 27,90 km by a Merino wether, and the least, 8,79 km, by an Angora goat doe. These results are still fragmentary and must be regarded merely as an indication of differences between breeds and types. It is possible that RTD-indices could differ greatly from those shown here, but it is expected that the ranking orders would remain approximately the same.
Much research remains to be done on the determination of RT-factors and RTD-indices. In further researches on Karoo veld it would be profitable to determine to what extent the factors and indices are affected and modified by the physical condition of breeds and types, vegetation type, fodder quality and quantity, topography and ground surface configuration, camp size and shape, placement of watering points, stocking density, interaction between breeds running together, disturbance of the surface of different types of soil (chipping effects, compaction and water infiltration), and influence of weather and season. Louw, et al., (1948) have already pointed out that the shape of the camp could have influenced walking distances especially in respect of the distance from watering points. Further aspects that have direct bearing on soil and vegetation disturbances are the distribution patterns of hoof prints e.g. footpath formation and overlapping and overtrampling of hoof prints. Roux (1967) has found that under high density stocking (21 Merino ewes on 3,1 ha for 14 days) 5,5 km of primary- and 15,9 km of secondary footpaths developed. Hoof prints covered 20ro of the ground surface.
A very significant aspect of trampling, at this stage ol1lY to be speculated on, is its effect, per season; on the composition of the vegetation, as well as the effect of trampling on the stimulation and or destruction of seedlings.
Overall it appears that trampling is a major factor in the grazing ecosystem and as yet largely unexplored on Karoo veld. A study (Du Toit, 1987) has recently been completed on aspects of the physical effects of sheep on different soil characteristics in the Karoo. This work will contribute to further understanding of direct grazing effects such as trampling.
The classical work of Arnold & Dudzinski (1978) provides further illuminating background information on animal behaviour and its effects and should be studied by those interested in the ethology of grazing animals.
ARNOLD, G.W. & DUDZINSKI, M.L., 1978. Ethology of free-ranging domestic animals. Developments in Animal & Veterinary Sciences 2, Elsevier, Amsterdam.
DU TOIT, G. VAN N., 1987. Die fisiese uitwerking van beweiding deur skape op verskillende grondeienskappe in die Karoo. M.Sc.-tesis. UOVS.
ENGLAND, G.J., 1954. Observation of the grazing behaviour of different breeds of sheep at Pantyrhuad farm, Carmarthenshire. Brit. J. Anim. Behav. 2 (2), 56 - 60.
LOUW, D.J., HAVENGA, C.M. & HAMERSMA, J., 1948. The walking habits of sheep. Fmg. S. Afr. 23,753 - 755.
ROUX, P.W., 1967. Die onmiddellike uitwerking van intensiewe beweiding op gemengde Karooveld. Hand. Weidingsveren. S. Afr. 2,83 - 90.
ROUX, P.W., 1979. Elements of the trampling factor in stock. Karoo Agric 1 (2), 9 -12.
Karoo Agric 3 (9), 8-10