- Effect of the level of energy supplementation on reproductive outcome and mohair production of pregnant goat ewes grazing Oldman Saltbush
|Last update: March 27, 2012 10:55:40 AM|
Effect of the level of energy supplementation on reproductive outcome and mohair production of pregnant Angora goat ewes grazing Oldman saltbush
Verena Hobson & P D Grobbelaar
Animal Production Research
Grootfontein College of Agriculture
Private Bag X529
Middelburg Cape 5900
To overcome periodic droughts, the cultivation of drought resistant fodder crops as a fodder reserve for sheep is a highly recommended practice. Oldman saltbush (Atriplex nummularia) has proved to be a very useful crop for this purpose. It is well known, however, that while the protein content of the edible material is relatively high (21 percent), the energy content of this fodder is relatively low. Consequently, Oldman saltbush provides only a maintenance ration for woolled sheep.
Previously no research has been done on the performance of Angora goats grazing Oldman saltbush. These animals are known to be sensitive to an energy deficiency and, especially while gestating, such a deficiency is manifested in the incidence of abortion. An experiment has recently been concluded at Grootfontein to evaluate Oldman saltbush as a fodder for Angora goats and to establish the optimal level of energy supplementation for reproducing ewes.
Within 30 days after mating, 32 newly shorn adult Angora ewes were transferred to Oldman saltbush paddocks. Experimental animals were allocated at random to the following treatment groups:
Group 1 Control. grazing Oldman saltbush only.
Group 2 Grazing Oldman saltbush and supplemented with 200 g chocolate maize/ewe/day.
Group 3 Grazing Oldman saltbush and supplemented with 400 g chocolate maize/ewe/day.
Group 4 Grazing Oldman saltbush and supplemented with 600 g chocolate maize/ewe/day.
After almost all the leaves of bushes in a paddock had been grazed, the animals were moved to the next paddock.
Live body mass of all experimental animals was recorded at weekly intervals. Animals were kept on the Oldman saltbush pasture for the entire gestational period, after which they were shorn and the mohair analysed.
Results and discussion
With the exception of one abortion in the control group, all experimental animals kidded normally. The fact that only one ewe aborted in the control group, seems to indicate that Angora ewes can readily satisfy their energy requirements for the maintenance of pregnancy on Oldman saltbush. However, it is reasonable to assume that such animals will run a relatively high risk of aborting, especially if an increase in the demand for energy occurs e.g. during cold spells, after shearing etc.
The changes in live body mass of the various groups are illustrated graphically in Figure 1. From this figure it is apparent that Group 4, supplemented with 600 g chocolate maize/ewe/day, showed the highest increase in live body mass while the control group maintained a virtually constant mass. Groups 2 and 3 were intermediate between these extremes with Group 3 (400 g) slightly ahead of Group 2 (200 g).
According to these results and from a cost-effective point of view, the choice for the optimal level of supplementation to pregnant ewes should be between 200 and 400 g of chocolate maize/ewe/day. This accords with the generally recommended supplementation of 300 g/ewe/day for pregnant Angoras grazing natural Karoo pastures.
Results on the effect of various levels of supplementation on mohair characteristics are summarised in Table 1. No significant differences occurred between the various groups for all traits measured. Although Group 4 (600 g) had an average fibre diameter of 38,5 .u as compared to 34,7 µ for the control group - indicating a positive effect of supplementation on fibre diameter - this difference was overridden by the variation between individual animals.
The results of this trial indicate that Oldman saltbush can serve as a useful source of fodder for Angora goats during periodic droughts. However, a moderate level of supplementation to pregnant ewes grazing Oldman saltbush is advisable to limit the risk of abortion. Such levels of supplementation will not affect mohair quality detrimentally.
Karoo Agric 3 (5), 1-3