- Fibre production VS hardiness: the choice
|Last update: August 17, 2011 02:04:40 PM|
Fibre production VS hardiness: the choice
When breeding woolled sheep, it is of the utmost importance that one should not look at the genetic side only - the environment must also be taken into account, especially with regards to nutrition.
Research suggests a negative relationship between fibre production potential and fitness or hardiness, says Dr. Danie Wentzel, Deputy Director, Karoo Region of the Department of Agriculture.
Addressing a symposium to mark the 25th anniversary of the Dohne Merino Breed Society at Thaba 'Nchu, he seriously questioned the policy of striving towards higher fibre production (fleece mass) in the extensive semi-arid areas of the country. He also expressed concern about the use of grain in the diet of breeding stock as it could have a negative effect on selection.
He told the audience that many years of extensive research on the Angora goat, the most effective fibre producer among the small stock breeds, resulted in some interesting findings, which also had a bearing on wool sheep.
Although the Angora is the top fibre producer (followed by the strong wool Merino, fine wool Merino and Dohne Merino, SA Mutton Merino and Afrino), it is also well known for its characteristic reproduction problems. Furthermore, the frequent losses of varying numbers of animals during cold spells and the poor growth rate of young animals, coupled to an exceptionally high mortality rate add to these constraints.
Comprehensive research has contributed to better understanding of the complex relationships between the various physio-endocrine mechanisms involved in the process of fibre production, tissue growth, reproduction and the maintenance of other body functions.
"This has been proved experimentally as well as in practice, and lends substantial support to the hypothesis that selection for mohair production results in a reduction of adrenal function - thus the secretion of andreno-corticosteroids, thereby reducing the constraints limiting fibre production. This condition will lead to the following metabolic adjustments," said Dr. Wentzel.
- Reduced ability to maintain the blood glucose levels under stressful conditions
- Reduced gluconeogenesis
- Reduced fat deposition
- Reduced ability to mobilise fat reserves
- Reduced voluntary feed intake
- Reduced resistance to cold
- Increased fibre production
- Increased fibre diameter.
Furthermore, it was estimated that these animals required four times more energy for fibre production than the for body growth. In view of these findings, coupled with the existing knowledge about the physiological and hormonal mechanisms of the Angora, the typical problems of the breed, which were without exception related to an energy deficiency, had been attributed to a condition of adrenocortical insufficiency.
In view of this it was apparent that most of the problems experienced by mohair producers could be solved by supplementation with starch-containing feed capable of increasing blood glucose levels. Chocolate grain proved to be particularly successful.
Although not to the same extent, a similar situation prevails in the wool industry where those animals with the highest fibre production potential suffer most in sub-optimal environments.
Recent research at Grootfontein decisively proved the inverse relationships between wool production potential and "fitness" or "hardiness" or "survivability".
Under favourable conditions wool production potential posed no problem. However, the picture changed considerably when conditions became less favourable and the nutritional requirements of the animal were not satisfied. The high potential for fibre production then became a serious constraint for survival.
Unfortunately the current economic conditions call for a "low input" animal, capable of producing and reproducing under extensive grazing conditions without feed supplementation.
"For optimal production it is important to farm with a well-adjusted animal which is suited for a specific area. To select for increased wool production in an area where the nutritional value of the natural grazing is low, will be a costly exercise because such a farmer will have to provide additional feed if his animals are to maintain a high production level."
Dr. Wentzel also queried the use of grain in the diets of breeding stock as it could seriously impair selection, especially with regards to fitness traits.
"When the diet of stud stock is supplemented with grain, it will be virtually impossible to identify the animals which could be better performers under more stressful conditions.
"Unfortunately the stud breeder is being forced to feed (or overfeed) his animals because many flock farmers still prefer well-fed rams. The flock farmer simply will have to realise that in future he will be able to achieve effective genetic progress in his flock only by purchasing the best performers out of a similar environment.”
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