- Diet of hamels and ewes on mixed Karoo veld
|Last update: March 29, 2012 08:43:42 AM|
The diet of hamels and ewes on mixed Karoo veld
An interesting trial to determine the dietary selection of Merino hamels and ewes on mixed Karoo veld was undertaken by the Karoo Region Agricultural Research Institute, Middelburg, Cape. In this article Mr P Botha of the Institute discusses the findings.
A TRIAL to determine the dietary selection of Merino hamels and ewes on mixed Karoo veld was undertaken over a period of two years at Grootfontein College of Agriculture. Oesophageally fistulated Merino hamels and ewes were used to collect dietary samples. Collection of the selected diet was done on four consecutive days every three months. The samples of the diets were examined microscopically to determine which plant species and the quantities thereof that had been selected by the animals. Four hamels and ewes were used to determine the selection pattern of the Merino on veld composed of 60 per cent bushes and 40 per cent grass.
The composition of the animals' diet during the various samplings is shown in figures 1 and 2. In these figures the contributions of the various components of Karoo veld, viz. palatable and unpalatable bushes, grass and herbaceous plants (opslagplante) to the diet of the Merino are given. For the division of the plant species into their various components, a list by Blom (undated) was used. The percentage of similarity in the diets of the two sexes during the various seasons and the average per year is reflected in tables 1 and 2.
In order to facilitate the discussion of the results, the diets of the animals during the various seasons of the year will be dealt with separately.
During this period the plant species selected by the two sexes corresponded by 81 per cent, though the quantities selected differed, with the result that the quantitative diets corresponded by only 57 per cent. During all three winter samplings the hamels concentrated on the palatable Karoo bushes (fig 1), and in all cases Salsola calluna (swartganna) was an important component of the diet. Amongst the unpalatable Karoo bushes, which played an important role in the diet of the hamels, were Aptosimum depressum (Karoo violet), Senecio leptophyllus (sambokbossie), Pentzia globosa (bitter Karoo) and Rosenia humilis (perdekaroo).
The Merino ewes appeared, according to figure 2, to concentrate on the palatable Karoo bushes, particularly during the first and last winter samplings, and during the other two winter samplings on the grass component, though an appreciable quantity of palatable bushes was also selected. As in the case of the hamels, Salsola calluna (swartganna) was the most important palatable bush in the diet of the ewes, though it was present in smaller quantities. Other palatable Karoo bushes which were present in the ewes' winter diet in reasonable quantities were Atriplex suberecta (wildelusern) and Felicia muricata (Karoo-aster). The annual herbaceous plant, Salvia verbenaca (salie) was the most important of the herbaceous species in the animals' diet during the winter samplings.
In spring there was an average overlap of 71 percent in the species composition of the diets of the two sexes. Because of the varying percentage of the different plant species in the diet, there was (on a quantitative basis an average) an overlap of only 35 per cent in the diets of the hamels and ewes.
During the first spring sampling the hamels concentrated mainly on the unpalatable bush component (± 30 per cent) and the palatable bush component (± 30 per cent) while the ewes concentrated overwhelmingly on unpalatable components, namely some 61 per cent. In both cases Galenia procumbens (kraalbos) was the most important unpalatable bush in the diet: in the case of the ewes, some 58 per cent and in the case of the hamels, some 21 per cent. Regarding the palatable Karoo bushes, Salsola calluna (swartganna) was the most important species in the diet of both sexes, but again at different percentages: 27 per cent for the hamels and 19 per cent for the ewes. Annual herbaceous plants, and in particular Salvia verbenaca (salie), comprised some 20 per cent of the hamels' diet, while this component was virtually absent from the ewes' diet.
During the second spring sampling the hamels concentrated mainly on herbaceous plants, particularly the annual Gasania krebsiana (buttercup) and the perennial Osteospermum calendulaceum (stekelblaar bietou) and on a large number of palatable Karoo bushes. The Merino ewes, on the other hand, concentrated on grass during this period. Some 57 per cent of their diet comprised grass.
The summer diet of the Merino hamels and ewes showed the greatest degree of similarity of all the seasons on a quantitative basis, namely 71 per cent. The overlap in respect of common species was about 66 per cent. This means that the percentage occurrence of the common species was very similar, and that there were also species present which were encountered in the diet of only the one sex.
During the first summer sampling, grass comprised the greatest part of the diet of both sexes, namely 49 per cent for the hamels and 54 per cent for the ewes. During this sampling the animals also selected an appreciable quantity of the annual herbaceous plant Salsola kali (rolbos).
The second summer sampling was noted, in as far as it concerned the hamels' diet, for the considerable selection of the palatable Karoo bush component (49 per cent), and particularly of Salsola calluna (swartganna), which comprised some 43 per cent of the animals' diet. The ewes on the other hand selected more or less even quantities of herbaceous plants and palatable bushes, namely 40 per cent and 44 per cent respectively.
Herbaceous plants, particularly Gnaphalium glomerulatum (groenbossie) (48 per cent) and Salsola kali (rolbos) (24 per cent), were the most important dietary component during the first two days for this sampling of the ewes' diet. On the other hand, during the last half of the sampling the palatable Karoo bushes were the most important dietary component. Again it was Salsola calluna (swartganna) which was the most important species in the diet, comprising as it did some 60 per cent of the total diet.
During this season the average diet of the Merino hamels and ewes corresponded by some 77 per cent in respect of the plant species selected. However the overlap regarding the quantities of selected species dropped to about 58 per cent because of the varying percentages to which the common species were present in the diet of the two sexes.
The diet of both sexes during the autumn samplings was characterised by a good representation of all the various dietary components. In the case of the Merino hamels the palatable Karoo bushes constituted the greatest portion of the diet (40 per cent), while the other three components each constituted some 20 per cent of the diet. During this period the ewes concentrated overwhelmingly on grass (46 per cent), while the palatable bushes constituted some 27 per cent of the diet. The palatable bush Trichodiadema pomeridianum (hairy nipple) was the most important single species in the diet of both sexes: some 17 per cent and 12 per cent in the case of the hamels and ewes respectively.
The second autumn sampling was characterised by an appreciable selection of Homeria pallida (geeltulp). This species comprised 44 per cent of the hamels' diet and 35 per cent of the ewes' diet. The two sexes selected the other components of Karoo veld in more or less equal quantities, but the species preferred varied. The hamels selected a wide range of species, particularly of the unpalatable components, in roughly equal quantities, namely Dimorphotheca zeyheri (bietou), Galenia procumhens (kraalbos) and Pentzia globosa (bitter Karoo), all of which comprised some 4 per cent of the diet. The ewes on the other hand also selected Dimorphotheca zeyheri (some 15 per cent), but also many annual herbaceous species, particularly Salsola kali (rolbos).
To summarize, it can be stated that the quantitative diet of Merino hamels and ewes corresponded by about 56 per cent. The greatest overlap (about 72 per cent) occurred during the summer months. During this period both sexes concentrated mainly on grass and herbaceous plants. There was least overlap (about 35 per cent) during the spring months. The hamels selected more or less equal quantities of palatable bushes, unpalatable bushes and herbaceous plants (31 per cent, 29 per cent and 23 per cent respectively) during the spring months. On the other hand, the ewes concentrated more on the unpalatable Karoo bushes (42 per cent), while grass constituted about 33 per cent of the diet compared with 8 per cent in the case of the hamels.
As far as species selected in common by the hamels and ewes is concerned there was an average overlap of approximately 75 per cent. This calculation does not take the percentage at which the species are present into consideration, but merely if it is present or not.
The greatest percentage of common species in the diet of the two sexes occurred during the winter months, viz. 8 per cent. During this period both sexes concentrated particularly on the palatable Karoo bush component (61 per cent for the hamels and 50 per cent for the ewes) and the unpalatable Karoo bushes (20 per cent and 13 per cent for the hamels and ewes respectively).
In general the selection pattern of both the hamels and ewes corresponded with the relative growth activity of the Karoo veld (fig 3). Generally the various components were selected when they were actively growing - Karoo bushes during the autumn and spring and grass during summer. Because the bushes were relatively greener than the grass in the winter, they played a greater role in the diet at that time.
Since the animals select plants during their most active growth periods, repeated grazing during the same season can lead to a decline in the actively growing component in the particular period. It is thus of the greatest importance to incorporate alternate rest periods in the veld management system. In this way every component is given an opportunity to grow undisturbed and to reproduce. This will ensure a generally virile Karoo veld.
Golden Fleece 14 (5)