Last update: March 29, 2012 10:36:07 AM E-mail Print



 P.G. Marais

Agricultural College, Middelburg, C.P., 5900


The introduction of nutritional systems to increase small-stock production in South Africa necessitates an in-depth look at the physiological requirements of the animals for increased production as well as the nature of the available nutrition. It is possible that certain physiological aspects of small stock can strategically be associated with specific nutritional factors in certain quantitative and qualitative nutritional deficiencies, the correction of possible imbalances and the more efficient utilisation of low-grade roughages.

Traditionally, small-stock production in South Africa is extensive, coupled to which is the fact that the available feeds - whether in terms of pastures or crop remainders - generally leave much to be desired. The natural veld is, regrettably, prone to deterioration and/ or modification, resulting in a drastic decrease in the production abilities and grazing capacity of this vast source of nutrition. The small-stock industry and its sources of nutrition are, therefore, in danger. In 1923, the Drought Investigation Committee was appointed with the view to reporting on factors which, in particular, threaten the small stock industry in South Africa, and to make recommendations for the protection of the industry. The same problem situation exists today. It is an undeniable fact that as far as animal production is concerned, livestock numbers have long ago increased beyond this country's potential. Add to this the population growth – which has already increased disproportionately, apart from the increased income of the working class - and one realises that the production per small stock unit will have to be increased drastically. One of the keys to this objective is efficient nutritional systems.


Reproduction and Nutritional Level

The production efficiency of an ewe for a particular period is determined by her reproduction ability (ovulation rate and lambing percentage), lambing frequency and slaughter mass of her lamb. Production costs can partly be measured according to nutrient intake, which can also be expressed in terms of grazing capacity per hectare. The level of feed consumption is firstly influenced by the size of the ewe, especially in relation to maintenance requirements, which can be as high as 75% of the total feed consumption. Secondly, lambing percentage and growth rate are just as important. The production efficiency of the 'ewe' improves if the number of lambs per year increases, because the ratio of maintenance cost to revenue per ewe improves correspondingly.

The body mass of the ewe at the time of mating has a significant influence on ovulation rate. It is essential, therefore, that during ovulation ewes should be in good condition without being overfat. Ewes which are on a high nutritional level up to 16 months have abetter oestrus activity than those with a low nutritional intake. In the case of mature ewes, oestrus activity is also influenced by the nutritional level. On a low nutritional level, Merino ewes have had 11,2 oestrus cycles during a breeding season of 206 days, compared with 7,2 in a breeding season of only 138 days. Good nutritional systems, therefore, reduce the breeding season and increase the number of oestrus cycles that can lead to fertilisation. For example, a high nutritional level has increased lambing percentages from 53% to 86%.


Wool Production and Nutritional Level

The influence of nutrition on wool production is almost as significant as it is on body mass. Research workers at this College have demonstrated this effectively when they compared various groups of Merino wethers which had grazed separately on Merxmuellera-, Merxmuellera-Pentzia and Pentzia veld, or had been fed lucerne hay in kraals. Using the lucerne group for control purposes, the Merxmuellera group produced 51% less clean wool, the Merxmuellera- Pentzia group 38% less and the Pentzia group only 9% less.

Australian research workers have also found that if the ration contains 7,5% crude protein, the wool growth is not affected by the protein percentage of the ration, but dependent on energy intake. This increase only applies to non-producing animals. It has furthermore been indicated that high (20%) and low (8% ) protein rations result in almost the same quantity of protein in the lower digestive tract. Micro-protein production in the rumen therefore appears to be a function of the quantity of digestible organic material in the rumen and as a result it is influenced by the quantity of energy available for the microbes. One can therefore conclude that wool production is not only related to the quantity of sulphurous amino acids reaching the lower digestive tract, but also to the extent of digestible energy in the diet.

If the production of progeny and of fibre are, therefore, to serve as criteria for efficiency, it is evident that nutrition is; a major factor in any programme aimed at production increase. It is thus essential that certain feeding problems in South Africa be looked at critically.


Grass-veld and Crop Remainders

The main problem with grass-veld and crop remainders in South Africa is their low digestibility and the nutritional value of winter-grass, winter crop remainders and maize leaves and stalks. After many studies on the problem of small stock on winter grass-veld, it appears that loss of body weight and decreased wool production during this season are significantly high. In both cases losses are in the vicinity of 20% or more. Seeking ways to prevent these losses is, therefore, justifiable and essential. Any nutritional practice which would prevent losses through supplementary winter-feed should, therefore, be applied in the most economical fashion while those facets of the industry which justify such practices, should be taken into account.

The results of digestion trials with Merino wethers, during which rumen-stimulating licks had been added to roughages of varying qualities, have proved clearly that the reaction to lick supplementation improves if the quality of the roughage improves. Another aspect that comes to light from this data is that a supplementary lick can only develop the inherent value of any roughage - nothing more. In the case of crop remainders and winter-grass the digestibility can only be increased to about 45% , which is the lower maintenance limit.

The economy of seasonal bridging on these plant materials is, therefore, the predominant factor. It has been found that mature Merino wethers can retain their body mass on low-grade roughages of which the digestibility has been increased to 45% by means of lick supplements. This rule applies to any mass of the animal within practical limits; in this particular case it was between 36 kg and 50 kg.

The practical implication of this finding is that animals can attain optimal physical condition on summer pastures plus lick supplements, and they can be kept at a reasonably high body mass throughout the dry season without losing production factors. Apart from the increased utilisation of low-grade roughages by means of lick supplements, much attention has also been given to the physical and chemical processing of these materials.

Compared with unmilled roughages, the milling, process not only results in a much-improved feed intake, but also in increased animal production. It has been found at this College that by feeding sheep milled lucerne hay, the following increases occurred: intake: 27%; mass increase: 150% (40 g/day compared with 100 g/day) and feed conversion efficiency: 49%.

Low-grade roughages have about the same gross energy value per mass unit as high quality feeds. The main problems is that structural carbohydrates in straw are not broken down by rumen micro-organisms with the result that the digestibility of the feeds as well as their metabolizable energy content are low. By treating such feeds with caustic soda, their physical structures probably change in that they become more accessible to rumen microbes and that structural carbohydrates are partially dissolved. It seems meaningless, however, to use more than 5% caustic soade; in fact, higher concentrations have an adverse affect on voluntary intake.

In their whole forms, most grains are regarded as highly palatable feeds and an over-intake easily occurs, resulting in dyspepsia among stock that are not adapted to diets of high concentrates. To avoid this problem - especially where large quantities of maize must be fed as an energy source - chocolate maize can be fed with very good results.



The production abilities of our livestock can be improved in two ways through feeding systems. Firstly, they can be increased through intensification, such as introducing tame pastures in the production system and applying creep feeding of lambs. Farming conditions in South Africa are of such a nature that these practices can only be applied to a limited extent.

Because of the fact that principally, the small-stock industry is concentrated in the extensive and less favourable climatic regions of the country, nutritional systems that are designed to increase production are mainly aimed at the improved utilisation of low-quality roughages. Among others, this can be attained with supplementary feeds and chemical treatment.



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