Grazing behaviour and diet selection by Dorper sheep
T.S. Brand
*Elsenburg Agricultural Research Centre, Private Bag X1, Elsenburg 7607, South Africa
Abstract
The grazing behaviour and diet selection by Dorper sheep, as well as other related aspects (pasture intake, walking habits and trampling) is reviewed. It was clear that Dorper sheep are less-selective grazers, compared to Merino-type breeds. Dorpers utilised shrubs and bushes to a greater extent, but grass to a lesser extent in relation to Merino sheep. The Dorper also utilised a larger number of different plant species than Merinos. Dorpers walked less to select food, or a suitable spot to graze, which consequently led to a shorter grazing time and less separate grazing periods. Dorpers consumed less herbage per metabolic size compared to Merino-type sheep. No uniform pattern in the walking distance of Dorpers was observed when compared to other sheep breeds. The relative trampling factor for Dorper sheep was less than that of evaluated Merino-type sheep. The review revealed a lack on information on the grazing behaviour and diet selection of Dorper sheep under more intensive grazing conditions. There is also a total lack of scienti®c information on other behaviour aspects of this unique breed.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Dorper sheep; Diet selection; Grazing behaviour; Walking habits; Pasture intake
1. Introduction
Large parts of South Africa are described as desert or semi-desert, and are suitable for sheep farming only. There was, therefore, a need to create a tough, non-woolled mutton breed with excellent meat and milk production characteristics, combined with hardi-ness, to adapt to the prevailing conditions in the extensive parts of the country (Bonsma, 1944). Cross-breeding experiments to achieve this goal were started in 1930 by the Department of Agriculture and led to the decision to use the Dorset HornBlack Headed Persian cross for the new breed in 1942 (Nel,
1993). The history of this new breed, the Dorper, was integrated with sheep farming in the barren and semi-barren North Western Cape area of South Africa (Nel, 1958). Erasmus (1961) reported that the most impor-tant characteristic of the breed was its hardiness and adaptation to dry and extensive veld conditions. Although the Dorper was initially selected only for areas in the country with a rainfall of less than 250 mm/year (Meyer, 1951), its adaptability and excellent characteristics led to the distribution of the breed throughout South Africa and the rest of the world. This review describes the behaviour of this unique breed with special reference to grazing beha-viour and diet selection. Localities throughout South Africa where grazing experiments with Dorper sheep were executed are illustrated in Fig. 1. Veld types were described according to Acocks (1988).
*Tel.:21-8844620; fax:21-8844226. E-mail address: [email protected] (T.S. Brand)
2. Diet selection
The Dorper is described as a hardy sheep breed, which can thrive under poor veld conditions. It is also believed that the breed is a strong and non-selective grazer (South African Stud Book and Livestock Improvement Association, 1998). A lot of studies have been done to verify this point and to compare the diet selection of Dorpers with other sheep breeds or other small stock and animal species.
2.1. Physical composition
Aucamp (1979) studied the diet preference of Dor-per sheep and Boer goats in die Valley Bushveld near Stutterheim in the Eastern Cape. The main plant component of Valley Bushveld is semi-succulent thorny bushes and grasses. The two animal species
grazed the veld at two stocking rates (6 Dorper ewes plus 8 lambs on 21 ha and 40 Dorper ewes plus 42 lambs on 20 ha versus 6 Boer goat does plus 6 lambs on 20 ha and 42 Boer goat does plus 59 lambs on 21 ha). His results (Fig. 2) clearly indicated that Dorper sheep preferred grass (70.2%), while the goats preferred shrubs (80.6%). Stocking rate did not alter these preferences.
Botha (1981) studied the diet selection of different animal species on Mixed Karoo near Middelburg in the Eastern Cape. The contribution of the different components of Mixed Karoo veld to the diets of different animal species (Dorper sheep, Merino sheep, Boer goats and Afrikaner cattle) are presented in Fig. 3. He concluded from this study that Afrikaner cattle selected more grass (average of 56%) than the small ruminants (average of 14.8, 22.9 and 11.5% for the Dorpers, Merinos and Boer goats,
respectively). The small ruminants concentrated to a greater extent than the cattle on seasonal annuals, when available. It was also clear that small ruminants utilised more shrubs (average 56.8, 53.4 and 63.4% for the Dorpers, Merinos and Boer goats, respectively) than cattle (average of 33.7%). Botha (1981) accen-trated the fact that the small ruminants utilised a large value of shrubs that are regarded as unpalatable for sheep.
It was evident from a study by Botha et al. (1983) that a large variety of plant species were commonly selected by Dorper sheep as well as Merinos (82.42.3%), Boer goats (75.54.1%) and cattle (55.811.6%). The extent whereto the diets over-lapped was larger in genetically related small rumi-nants. However, when the extent of overlap in the diets was expressed on a quantitative basis (i.e. the percen-tage contribution of each plant specie was also
con-Fig. 2. Diet preferences and selection by Dorper sheep and Boer goats when grazing Valley Bushveld (Adapted from Aucamp, 1979).
sidered) less overlap were observed in diet selection between animal breeds and species. The diets selected by Dorper sheep overlapped with 61.05.3% (Merino sheep), 56.915.4% (Boer goats) and 31.76.6% (Afrikaner cattle), respectively, when expressed on a quantitative basis (Botha et al., 1983).
Roux (1992) determined the diet selection of Dor-pers and Merinos on both low and high time occupa-tion areas on Mixed Karoo at Grootfontein in the Eastern Cape. He observed that although there was a difference in botanical composition, both breeds tended to select the same types of diets on these areas (Fig. 4). His study clearly indicated that Dorper sheep selected more shrubs (35.7% versus 13.9%) while Merino sheep selected more grass compared to Dor-pers (86.1% versus 63.7%).
Du Toit (1998) studied the selective grazing beha-viour of Dorper and Merino sheep on three different veld types, that is Arid Karoo (Carnarvon), Mixed Karoo (Grootfontein) and Noorsveld (Jansenville) in the Eastern Cape area of South Africa. Oesophageal ®stula extrusa samples were collected during winter, spring, summer and autumn for 3 years, and micro-scopically examined and grouped into functional plant groups. In the Arid Karoo, Dorpers, selected more (11±18%) karoo bushes than Merino sheep, while Merino sheep during all seasons on the other hand, selected more (12±16%) grasses than Dorper sheep.
Similarly, in Noorsveld (except autumn), Dorpers selected more karoo bushes (8±11%) and Merinos selected more (8±15%) grasses. In Mixed Karoo, Merinos selected more grass (7±12%) while Dorpers selected more (6±13%) karoo bushes than Merinos over all seasons, except during summer. Merinos selected more karoo bushes and the Dorpers consumed a large quantity of annuals during this season. Com-bined data for all seasons, as adapted from Du Toit (1998), are presented in Fig. 5. It was evident that Dorper sheep concentrated their grazing more on the woody plant component, that is karoo bushes in the Arid and Mixed Karoo and the tree and shrub com-ponent in the Noorsveld, while Merino sheep concen-trated their grazing on grass. Du Toit (1998) concluded from his study that Dorper sheep was the less selective grazer of the two breeds, while the Merino was more selective.
Du Toit et al. (1995) compared diet selection of Afrino sheep (a 25% fat tailed Afrikaner, 25% Merino and 50% South African Mutton Merino cross breed), Dorper sheep, Merino sheep and Angora goats on Arid Karoo. He found that the diet selected by Dorper sheep differed 7±10, 6±9 and 6±45% from the diets selected by, Afrino sheep, Merino sheep and Angora goats (Table 1), respectively. Du Toit and Blom (1995) compared the diet selection of Dorper and Merino sheep and Angora and Boer goats on Noorsveld to
ascertain differences in their food preferences. The diet selected by Dorper sheep differed only between 2±13% from that of Merino sheep over the four
seasons. Differences in diet selection between Dorper sheep and Angora (7±33%) and Boer goats (26±55%) were much larger (Table 1). The mean overlap in diet
Fig. 5. Diet preferences and selection by Dorper and Merino sheep when grazing three different veld types (Adapted from Du Toit, 1998).
Table 1
The mean overlapain the selected diets of Dorpers and other small stock breeds and species on three different veld types (adapted from Du Toit et al., 1995; Du Toit and Blom, 1995; Du Toit, 1998)
Veld type and season Overlap between Dorper and other breeds and species
Afrino sheep Merino sheep Angora goats Boer goats Du Toit et al., 1995
Arid Karoo
Winter 0.91 0.91 0.55 ±
Spring 0.93 0.94 0.94 ±
Summer 0.90 0.92 0.91 ±
Autumn 0.93 0.94 0.70 ±
Du Toit and Blom, 1995 Noorsveld
Winter ± 0.87 0.83 0.74
Spring ± 0.98 0.93 0.57
Summer ± 0.97 0.80 0.51
Autumn ± 0.97 0.67 0.45
Du Toit, 1998 Mixed Karoo
Winter ± 0.97 ± ±
Spring ± 0.89 ± ±
Summer ± 0.75 ± ±
Autumn ± 0.75 ± ±
aAn index value of one indicate that the two animal groups being compared utilised very similar components. As the index value
selection of Dorper and Merino sheep on Mixed Karoo varied between 3 and 25% for the four seasons (Table 1) (Du Toit, 1998).
2.2. Chemical composition
Engels et al. (1974) studied the selective grazing behaviour of Dorper and Merino sheep when grazing a mixed type of natural veld (consisting of 60% The-meda triandra, 6% shrubs and the remainder a mixture of annual grasses) near Glen in the Free State area of South Africa. Samples were collected by oesophage-ally ®stulated (OF)-wethers over a 6-month period. The authors found that the differences between breeds with regard to chemical composition and in vitro digestibility were not signi®cant (Table 2). They concluded that the selective grazing behaviour of the Dorper and the Merino appeared to be similar on this veld type. De Waal et al. (1980) made similar observations in the same area (Themeda triandra, Eragrostis chloromelasand Cymbopogon plurinodis
were the prominent grasses, accounting for 61.8% of the basal plant cover), when compared the monthly OF-collected herbage samples of Dorper and Memo wethers over a 12-month period.
Aucamp (1979) studied the effect of animal specie (Dorper sheep or Boer goats) and stocking rate on the chemical composition of diets selected by OF-animals in the Valley Bushveld near Stutterheim. The author concluded from his results (Table 2) that Dor-per sheep and Boer goats selected material of different quality within the same veld type. Stocking rate depressed the quality of the material selected by both animal species.
In a study performed by Brand and Franck (1998), the quality of wheat stubble grazing were determined monthly over a 5-month period by OF Dorper and SA Mutton Merino wethers. The study was performed at the Langgewens Experimental Farm near Moorrees-burg in the Western Cape Province of South Africa. The grazing existed out of straw, weeds and residual ears and straw. The sheep grazed the stubble at two stocking densities (one or two ewe units/ha) for 154 days. Sixteen samples per breed were selected monthly for 5 months. Signi®cant breedstocking rate interactions occurred. No signi®cant differences in the quality of diets selected at the low stocking rate were found between breeds (Table 2). Dorpers, how-ever, selected diets with a lower CP and higher NDF content when grazing at the high stocking rate. It was
Table 2
The chemical composition and digestibility of pasture samples selected by different sheep breeds Breed Composition of selected sample (g/kg)
Ash CP DOM CF ADF NDF
Engels et al., 1974a
Dorper 168 116 568 300 ± ±
Brand and Franck, 1998a
Dorper: low 16026 14434 591NS11 35819 509110 Dorper: high 14115 8813 571NS12 480211 65939
SA Mutton Merino: low 1692,36 13936 565NS13 358112 524117
SA Mutton Merino: high 17938 10526 593NS12 468214 615214 aChemical composition on an ash free basis.
bChemical composition on an DM basis. cIndicate low and high stocking rates.
argued that, under the higher stocking density, Dorpers were willing to select samples of lower quality than SA Mutton Merinos.
3. Plant selection
The number of different plant species selected by an animal is an indication of the degree of selective grazing by the animal. In the study of Botha (1986), it was evident that Boer goats selected the highest number of plant species (i.e. 44 from a pos-sible 95). This was followed by Merinos and Dorpers (37±38 species), while Afrikaner cattle selected only 24 species. In a comparative study between Dorper and Merino sheep in Arid Karoo, Du Toit (1998), however, found that Dorper sheep selected a diet containing about 90% of the karoo bush species group, while the Merino sheep selected only between 60 and 65% of the karoo bush species group.
4. Grazing habits
Data on grazing habits of sheep is scarce in South Africa. Roux (1992) did the only experiment on the grazing habits of Dorper sheep at Middelburg in the Eastern Cape. Four camps of 0.5 ha on two different localities were used. The grazing habits of Dorper and
Memo sheep were recorded during January (®rst observation period) and March (second observation period). Observation of the daily movement of the sheep started half-an-hour before sunrise and ended half-an-hour after sunset. The time subdivision of physical activities of the two breeds is presented in Fig. 6. Data is presented as a percentage of time from 4:50±19:35 hours during the ®rst observation period and from 6:30±18:30 hours during the second obser-vation period. The average time that Dorpers spent grazing per day during the two observation periods was 465 and 525 min, respectively. This consisted of two, approximately equal grazing period each. Mer-inos grazed an average of 555 and 570 min/day, respectively. These grazing hours consisted of four or more separate grazing periods of different inten-sities during the day.
Dorpers avoided grazing in 50 and 36%, respec-tively, of their camps, while Merinos avoided grazing in 30 and 45% of their camps. Roux (1992) found that there were more periods of high intensity grazing on certain areas with Merinos than for Dorpers. The longest time Dorpers grazed on a particular area was 13±18 min, compared to 25±30 min for Merinos. Roux (1992) also observed that Merinos walked larger distances (2.75±3.50 km/day) to select food, or a suitable spot to graze. Dorpers walked shorter distances (1.80±2.23 km/day) to ®nd food and their next preferred grazing area was never far off.
Roux (1992) concluded that Memos were more inclinated to area selection grazing and in general grazed more selectively, compared to the Dorper which consequently utilised a greater spectrum of plant species.
Roux (1992) noted that the Dorpers did not visit the watering point for drinking during the daytime, while the Merinos did in fact drink water once a day in the afternoon. In contrast, Louw et al. (1948), however, concluded from his studies with different sheep breeds (Black Headed Persians, Black Headed Per-sianDorset Horn, Karakoel and Merino) that all breeds went to drink water once a day and that the time varied between 9 a.m. and 6 p.m.
A characteristic that is found in both the Black Headed Persian and the Dorper is the habit to creep through fences from one paddock to another (Nel, 1993). Although the thickness of their skins probably prevent them to get hurt while creeping through the fences, it is probably also related to their grazing habits, since this phenomenon occurred to a larger extent when grazing become scarce.
5. Pasture intake
Engels et al. (1974) determined the monthly volun-tary feed intake of Dorper, Merino and South African Mutton Merino wethers under free grazing conditions on mixed natural pasture (Glen) over a 12-month period. Their results indicated that the organic matter intake of the Merinos and SA Mutton Merinos was, with exception of 1 month, consistently higher than that of the Dorper. The average organic matter intake of the three breeds is presented in Table 3. It must, however, be stressed that the adult Dorper is heavier than the adult Merino which will consequently cancel this difference when expressed on an intake per sheep basis (Engels et al., 1974).
De Waal et al. (1981) also determined the monthly voluntary feed intake of young Dorper and Merino wethers at Glen on mixed natural pasture. Similar to the results of Engels et al. (1974), they found sig-ni®cantly higher DOM and CP intakes with Merinos compared to Dorpers (Table 3) when calculated on a metabolic weight basis.
Table 3
The voluntary feed intake of different sheep breeds under free grazing conditions Breed Average daily intake De Waal and Biel, 1989
Early lactation, 1981
Merino ± 47.4 g kg W075/749/g/day 115 g/day
Early lactation, 1983
Dorper ± 53.9 g kg W075/881 g/day 173 g/day Early lactation, 1984
In a subsequent study by De Waal and Biel (1989), the feed intake of lactating Dorper and/or Merino ewes were determined on grassveld in the Free State area of South Africa during ®ve seasons (1981±84). Differ-ences in herbage intake between breeds (1981±82) were relatively small (Table 3). Dorper ewes were heavier than Merino ewes, and thus, consumed less herbage per metabolic size than Merino ewes. De Waal and Biel (1989) ascribed the higher intake values during 1983 and 1984 to higher pasture availability as well as a possible substitution effect because of sup-plementary energy during 1981 and 1982.
6. Walking habits
Bonsma (1944) reported that the Dorset Horn -Black Headed Persian cross was active and hardy sheep, well adapted to the more extensive and arid regions of South Africa. Louw et al. (1948) argued that an animal, which is able to cover vast distances in a minimum time, would be able to go out in search of food in more arid regions of the country. He therefore conducted a study at Middelburg Cape in a 125 ha camp to compare the walking habits of different sheep breeds. In the ®rst study (during winter), four different breeds were compared (Table 4) to each other in either a single ¯ock or separate ¯ocks. In the second study (during summer), three separate tests were done and only selected combinations were compared to each other (Table 4). Louw et al. (1948) concluded from their studies that the Black Headed Persian and the Black Headed PersianDorset Horn walked the same distances each day, while the Merino and Karakoel breeds walked considerably less. All breeds walked considerably less during the winter compared to the summer, probably due to a shorter day-length.
In an experiment by Roux and Schlebusch (1987), different types of small stock and sheep breeds range together with a ¯ock of the same breed on Mixed Karoo vegetation on an area of 31 ha, while daily walking distances were monitored. Appreciable dif-ferences in the walking distances of breeds and types of small stock were indicated (Table 4).
Roux (1992) monitored the walking distances of Dorper and Merino wethers while grazing 5 ha pad-docks in separate ¯ocks of 10 each. He repeated his study in two paddocks per breed. In both cases, the
distance walked per day by the Merino wethers exceeded that of the Dorper wethers (Table 4). He argued that the Merinos walked more than the Dorpers to select food, or a suitable spot where they could graze. The Dorpers walked less to ®nd food and it appeared from his study that their next preferred grazing area was never far off.
7. Trampling
The damaging effects of trampling on veld, espe-cially in low rainfall areas, is well-known. Roux (1979) introduced the relative trampling (RT) factor, which includes elements like bodyweight, stride
Table 4
Distances covered by Dorper and other sheep breeds during ranging (km/day)
Sheep breed or animal specie Flock type Single flock
Separate flock Louw et al., 1948
Black Headed Persian 3.94 4.94 Black Headed PersianDorset Horna 3.77 5.10
Karakoel 3.18 3.47
Merino 3.14 3.60
Louw et al., 1948 Test 1
Black Headed Persian ± 7.72 Black Headed PersianDorset Horna ± 8.13 Test 2
Black Headed Persian ± 7.12
Karakoel ± 5.22
length and hoofprint area to measure the effect of trampling on the veld. The higher the RT-factor, the greater the potential ability to disturb surfaces by trampling. Roux and Schlebusch (1987) argued that the relative capacity of breeds or types of breeds to trample (RTD-index) can be re¯ected by RT-factordistance walked per day (D). Comparative RTD-indexes for some local small stock breeds are presented in Table 5.
Clear differences in RTD-indices between breeds and types of breeds existed, which accentuated the differences between breeds to trample during the process of ranging. The RTD-index of the Dorper ewes was approximately 6.5% less than that of Merino ewes.
8. The effect of grazing on the veld
Barnard (1987) compared the effect of different animal species on the change in veld composition in the Sandveld area at the Nortier Experimental farm
near Lambertsbaai in the Western Cape area of South Africa. The animals grazed the area for 7±13 years and plant surveys were done once a year. The change in the palatable and unpalatable plants as well as the grass component of the veld are presented in Table 6. Barnard (1987) ascribed the increase in total plants in the paddocks grazed by cattle for 13 years and Boer goats for 7 years to the increase in the grass compo-nent, although the palatable shrubs also increased by 17.0 and 8.7%, respectively. When this ®gures were compared to the paddocks grazed by Dorpers, it seemed that the unpalatable shrubs and grass compo-nents increased, while the palatable shrub component decreased. Barnard (1987) ascribed the decrease in the total plant component in the camps grazed by Merinos to the selective grazing behaviour of the breed. Barnard (1987) noted that Boer goats did more damage to the shrubs than expressed by the ®gures in Table 6.
9. Synopsis and conclusions
Clear differences in the diet selection of Dorpers and other sheep breeds occurred. Dorpers utilised shrubs and karoo bushes to a greater extent than Merino sheep. Merino sheep, under the same grazing conditions, concentrated more on grass as part of their diet. The Dorper also utilised a larger number of different plant species than the Merino.
The chemical composition of diets selected by Dorpers or Merino-type sheep did not differ when suf®cient grazing is available. When nutrients, however, became limited, the Dorper was willing to select samples of lower quality than Merino-type sheep.
Table 5
Relative trampling factor (RT) and RTD-indices for some small stock breeds on Mixed Karoo veld (Roux and Schlebusch, 1987)
Parameter
RT-factor RTD-index Angora doe 1.13 0.40 Boer goat doe 0.75a 0.43 Dorper ewe 0.84 0.54 Merino ewe 1.07 0.64 Angora kapater 1.20a 0.71 Merino wether 0.93 0.85
aEstimated values.
Table 6
The effect of grazing by different types of farm animals on veld composition (Adapted from Barnard, 1987) Treatment Sheep units/ha Period years Change in veld composition
De®nite differences exist in the grazing habits of Dorper and Merino sheep. Dorpers walked less to select food or a suitable spot to graze, which led to fewer separate grazing periods during the day. The total grazing time of Dorpers were also less than that of Merinos.
Merino-type sheep consumed more herbage per metabolic size than Dorpers. The Dorper is, however, heavier than Merino sheep, which consequently can-cel the differences when expressed on an intake per sheep basis.
No uniform pattern in the walking distances of Dorpers, when compared to other sheep breeds was observed. Generally, Dorpers walked less during graz-ing than Merinos, when ef®cient grazgraz-ing is available. Under more extensive conditions, however, earlier data revealed that Dorper sheep covered larger dis-tances during ranging than Merino sheep.
The relative trampling factor for Dorper sheep was calculated to be less than that of evaluated Merino-type sheep. This, due to the shorter distances covered during grazing, lead to a smaller trampling index for Dorpers compared to Merino-type sheep.
In an experiment to determine the effect of grazing by different types of farm animals on veld composi-tion, veld condition improved after utilisation by Dorpers for a relatively long period.
In conclusion, its evident that Dorpers were indeed less-selective grazer compared to Merino-type sheep. It also utilised a larger range of different plant species. Most of the available studies were, however, per-formed under extensive conditions. The unique graz-ing behaviour and diet selection of Dorper sheep will, however, also be of bene®t under more intensive grazing conditions. Future research on this subject will be worthwhile, especially in view of the fact that the breed is expanding to the rest of the world. Apart from grazing behaviour, a lack of scienti®c justi®ed information on other aspects of behaviour of Dorpers exists, which must be addressed in the future.
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