Last update: March 26, 2012 04:04:39 PM E-mail Print

 

Research on Angora goats over the past two decades

 

D. Wentzel

Animal Production Research

Grootfontein College of Agriculture

Private Bag X529

MIDDELBURG CAPE

5900


It is generally accepted that the mohair industry of South Africa is the leader among the mohair producing countries of the world. According to history, the present healthy state of this industry may partially be ascribed to the successful overcoming of problems, which hampered progress. In this respect Grootfontein played a significant role in the concerted efforts of scientists, applied scientists and producers to solve problems and enhance mohair production. The purpose of this paper is to review the major technical problems experienced by the mohair industry, the research done, the formulation of practical solutions and the eventual success achieved at producer-level.

 

MAJOR PROBLEMS, WHICH HAMPERED PROGRESS OF THE MOHAIR INDUSTRY

(i) Low reproduction rates resulting from, low conception rates, abortions and a relatively high kid mortality rate. Abortion has generally been regarded as the most serious problem as was indicated by a restricted survey which revealed alarming losses of up to 80% of the potential kid crop on some farms (Van Heerden, 1963). On average, kidding rates of less than 60% were generally accepted as being normal.

(ii) Frequent and severe losses of Angora goats during cold spells, especially among newly shorn animals, present a serious problem to the mohair producer. In the major mohair producing areas the losses suffered as a result L of adverse weather conditions, which quite often prevail in this region, could be disastrous.

(iii) Poor growth and production in young animals, run under extensive conditions, increase the mortality rate and contribute to a reduction in the life-time production of especially reproducing animals.

Recognition of the seriousness of these problems triggered off research aimed at providing practical solutions.

 

1.      Abortion

Initial investigation of this phenomenon eliminated the possibility of infectious diseases and mineral and vitamin deficiencies as a cause of premature pregnancy termination (Van Heerden, 1963). According to these results it appeared that the problem was related to a complex endocrine failure and several detailed and comprehensive studies of the endocrinology of pregnancy and abortion in the Angora followed (Van Heerden, 1963, 1964; Van der Westhuysen & Wentzel, 1971; Van Rensburg, 1963, 1964, 1965, 1970; Wentzel, 1973; Wentzel & Botha, 1976; Wentzel, Le Roux & Botha, 1976). These studies led to the eventual identification of two distinct types of abortion with completely different endocrine bases (Wentzel, 1973). In addition ample evidence was obtained that nutritional stress, and probably other types of stress as well, is instrumental in the abortion syndrome (Wentzel, 1973; Wentzel et al., 1976).

On account of these results it was postulated that the endocrine pathway, through which abortions induced by nutritional stress are mediated, originates from a drop in maternal blood glucose concentration. This primary trigger affects a similar hypoglycaemic condition in the foetal circulation, which activates the foetal hypothalamic-pituitary-adrenal-axis resulting in an elevated output of steroids, presumably oestrogen precursors. The latter results in an excessive placental secretion of oestrogens into the maternal circulation, which in turn mediates regression of the corpus luteum through the release of uterine prostaglandins. Finally, the consequent reduction of the progesterone level permits the onset of labour and hence delivery of the foetus (Wentzel, 1973). The aforementioned hypothesis was substantiated by subsequent studies in which an attempt was made to simulate some of these aetiological conditions.

The aetiology of the other type of abortion proved to be completely different.

According to these results it was postulated that a condition of chronic hyperadrenocorticism interferes with the normal regulation of the water and electrolyte balance of the body, causing placental dysfunction and thus the progressive accumulation of excessive intra-uterine fluids. The latter creates an unfavourable foetal environment, which results in foetal oedema, a retarded foetal heart rate and eventually congestive heart failure (Wentzel, 1973). It is therefore evident that the mechanism involved in abortions of this type is primarily responsible for intra-uterine foetal death. Expulsion of the dead conceptus is merely a consequence of the latter event and is probably mediated through uterine prostaglandin release, induced by autolysis of the dead conceptus, which in turn effects luteal regression. Finally, the resultant cessation of the progesterone block on labour, and other factors involved in normal parturition, permits delivery of the foetus.

The finding that stress, as exerted by sub-nutrition, especially as far as energy is concerned (Van der Westhuysen & Roelofse, 1971; Wentzel, Morgenthal, Van Niekerk & Roelofse, 1974), has such a substantial effect on abortion rate was of special practical significance. This provided an explanation for the more severe spates of abortion usually occurring during droughts and following adverse weather conditions. The only practical measure to limit these abortions is supplementation, especially of energy. Since this has been advocated, significant declines in abortion rate were reported from practice. According to further research and experience in practice it became evident that most of the abortions occurring under free-range conditions are of this type, induced by stress. This fact rendered the other type of abortion identified of very little practical significance.

Further observations in practice led to the identification of additional situations and/or conditions increasing the susceptibility of animals to abortion e.g. during inclement weather conditions; after shearing when the ewe is exposed to cold climatic conditions and the increased demand for energy is not met; when animals are moved from the veld to pastures and a temporary energy deficiency is induced by the period of ruminal adaptation to the new diet; when animals are sheltered for prolonged periods without the provision of feed; and that young or old and relatively small ewes are more prone to abort as a result of stressful conditions than well grown adult ewes.

 

2. Losses during cold spells

Research on this problem was aimed firstly at elucidating the physiological and endocrinological changes preceding death of the cold stressed Angora goat. Aspects related to metabolic heat production e.g. adrenal and thyroid function, blood glucose concentration, heart rate, rectal temperature etc. were monitored during this period. According to the results, young animals showed less tolerance to cold stress compared to adult animals, indicating some resemblance with the situation found in the abortion syndrome. The most significant feature elicited by this research, however, was an abrupt drop in blood glucose concentration associated with collapse of the cold stressed animal, suggesting that this condition is the crucial factor leading to the failure of the mechanism responsible for the required rate of metabolic heat production. This was confirmed by the rapid recovery of cold stressed animals following intravenous infusion of an isotonic glucose solution (Wentzel, Viljoen & Botha, 1979). The latter, however, does not offer a practical solution to the problem so producers were advised alternatively to administer a saturated glucose solution intraperitionally. Although this more practical method has met with considerable success during crises in practice it remained merely an emergency treatment and not a solution to the problem. Research on this aspect was therefore continued by way of another approach to the problem, viz. to increase blood glucose concentration through nutrition. Initial results indicated that the increase in circulating glucose is directly related to the amount of starch ingested by the goat (Wentzel, 1980 - unpublished results). The application of the latter concept in practice is however seriously limited by the risk of acidosis in free-grazing ruminants not adapted to high concentrate diets. Subsequent research was therefore aimed at overcoming the problem of acidosis. This has led to the development of alkali-ionophore-treated whole grain (commonly known as chocolate grain - Wentzel, 1982, 1983). This procedure allowed the ad lib. intake of treated  grain by goats not previously adapted to such diets without any danger of digestive disorders and acidosis. Furthermore animals having free access to  this treated grain showed average increases of 50-60% in circulating glucose levels within 48 hours after offering the grain. Of special significance was the finding that already within four hours an average rise in blood glucose of 12% occurred. During cold spells the timeous and rapid increase of the energy status of the cold stressed goat, achieved in this way, could be a crucial {actor to prevent serious losses.

Since the introduction of this new development into practice, it has proved to be a valuable management tool to revive cold stressed animals and/ or as a preventative measure to increase rapidly the energy status of the goat thereby increasing its tolerance to cold.

In addition to the primary purpose for which alkali-ionophore-treated grain was developed, it soon found several other applications in practice, especially to reduce abortion by strategic supplementation during the critical periods mentioned earlier, e.g. during droughts and cold spells, when pregnant ewes are sheltered in enclosures, after shearing and when the diet of ewes changes as a result of a change in pasture. In this respect the feeding of treated grain has proved to be highly effective to halt the physio-endocrine mechanism provoking abortion.

 

3. Poor growth in young animals

Poor growth in growing kids has been a serious concern of mohair producers, not only because of the direct loss in mohair production, but especially because of impaired reproduction experienced in such animals once they become adults. Surveys have shown that live body mass is one of the primary factors affecting reproduction (Shelton, 1961; Van der Westhuysen, 1971) especially in the maiden ewe at first mating e.g. a kidding rate of 86% was recorded in well-fed young ewes as compared to a kidding rate of only 19% in unsupplemented young ewes on Karoo pasture.

With due consideration of available information and the previously mentioned energy-related problems, research was concentrated on the effects of energy supplementation on growing kids grazing natural Karoo pasture. The results clearly indicated an energy insufficiency in the natural pasture and quite remarkable responses in growth rate were obtained with energy supplementation. In one trial supplemented two-tooth ewes weighed well in excess of 40 kg whereas the minimum mass set for successful reproduction at this age is only 27 kg.

The incidence of coccidiosis among growing kids was also identified as one of the serious limiting factors of optimal growth. Subsequent research revealed that this condition could be controlled effectively by the inclusion of antibiotic ionophores in the diet of kids.

In this respect chocolate grain once again found a valuable application, firstly as a supplement during various stages of the growth cycle, especially after weaning, to ensure optimal growth with several beneficial effects on subsequent reproduction, and secondly, the presence of antibiotic ionophores in the treated grain controls coccidiosis effectively. When kids are kept under conditions conducive to coccidiosis such as on pastures and in kraals, the inclusion rate of the ionophore can be easily adjusted to obtain an effective dose level for the specific situation.

Another application of this treated grain has evolved from research on the effect of flushing on reproductive performance of Angora goats (Loubser, 1983). Increases in kidding rate from 17 to 60% following flushing with 400-600 g of chocolate maize were obtained in various trials. This relatively good response to flushing is ascribed to the abrupt and rather dramatic increase in energy intake, which can be achieved only by the feeding of treated grain. By combining flushing with mating during the peak of the breeding season a high occurrence of oestrus synchronization is achieved with several advantages as far as management is concerned. The fact that 75-85% of the breeding flock can conceive within the first two weeks of the mating period when flushing has been applied successfully, reduces the flushing period considerably. This has made the practice much more cost-effective and acceptable to producers.

It should be mentioned that the use of treated grains has also found widespread application in other small stock industries and is at present commonly used for fattening of sheep, drought feeding and supplementation purposes, and for prevention of pregnancy enterotoxaemia in sheep.

The most common problem experienced in practice with the feeding of chocolate grain was the incidence of scouring which in most cases was traced back to either the omission of the ionophore or the use of calcium carbonate instead of calcium hydroxide. However, a problem which came to the fore and which called for further research was the incidence of urinary calculi formation in male animals, especially well-fed rams, resulting from the excessive intake of treated grain and thus an excessive intake of phosphorus. Investigation of this aspect showed that the problem was greatly alleviated by the use of calcium hydroxide instead of sodium hydroxide thereby correcting the Ca:P imbalance normally found in grain. The inclusion of 0,5-1 % ammonium chloride in the recipe for preparing this treated grain to acidify the urine has virtually resolved the problem.

It should also be mentioned that a handbook was compiled on Angora goat farming in South Africa (Van der Westhuysen, Wentzel & Grobler, 1985) covering all practical aspects and management practices which have evolved from the interaction between science, applied science and practice. This publication has greatly contributed to the dissemination of information, relevant to improved mohair production, among producers. At present it can be accepted that virtually all established mohair producers are cognizant of the pitfalls of Angora goat farming and that the practical measures to overcome these pitfalls are implemented extensively. This is reflected in the improvement of mohair production during the past two decades. Reproductive rate has increased from less than 60% to a present rate approximating 80%, while average mohair production per animal has increased from 3,18 kg in 1960 to more than 4 kg at present. This represents the highest average mohair production per animal in the world. Furthermore, the alarming abortion rate mentioned earlier are virtually unknown today.

In retrospect, it is apparent that the combined efforts of researchers, applied scientists and producers have significantly improved Angora goat and mohair production. Continued collaboration between these parties is imperative for maintaining a high level of production, especially in view of the significant expansion of the mohair industry and of rapidly changing economic considerations.

 

REFERENCES

LOUBSER, P.G., 1983. Die effek van prikkelvoeding op die reproduksievermoë van Merinoskape en Angorabokke. Karoo Agric. 3, 21.

SHELTON, M., 1961. The relationship of size to breeding performance of Angora does. Agric. Exp. Sta. Res. Bull. no. 2339,18.

VAN DER WESTHUYSEN, J.M., 1981. Selection for reproductive efficiency. Angora Goat Mohair J. 23, 43.

VAN DER WESTHUYSEN, J.M. & ROELOFSE, C.S., 1971. Effect of shelter and protein on reproductive performance in Angora goats with special reference to the habitual aborter. Agroanimalia 3, 129.

VAN DER WESTHUYSEN, J.M. & WENTZEL, D., 1971. Progress through selection against the aborting Angora goat. S. Afr. J. Anim. Sci. 1, 101.

VAN DER WESTHUYSEN, J.M., WENTZEL, D. & GROBLER, M.C., 1985. Angora goats and mohair in South Africa. Sec. Ed. NKB printers, Port Elizabeth, RSA.

VAN HEERDEN, K.M., 1963. Investigations into the cause of abortions in Angora goats in South Africa. Onderstepoort J. Vet. Res. 30, 23.

VAN HEERDEN, K.M., 1964. Effect of culling aborting ewes on the abortion rate in Angora ewes. Angora Goat Mohair J. 6,15.

VAN RENSBURG, S.J., 1963. Endocrinological aspects of habitually aborting Angora goat ewes. S. Afr. med. J. 37, 114.

VAN RENSBURG, S., 1964. Possible endocrine mechanisms in gestational failure. Proc. Vth Int. Congr. Anim. Reprod., Trento, 3, 375.

VAN RENSBURG, S.J., 1965. Adrenal function and fertility. S. Afr. vet. med. Ass. 36,491.

VAN RENSBURG, S.J., 1970. Reproductive physiology and endocrinology of normal and habitually aborting Angora goats. D.V.Sc.thesis, Univ. Pretoria.

WENTZEL, D., 1973. The habitually aborting Angora doe; Recognition and endocrinology of two types of abortion. Ph.D.(Agric.) thesis, Univ. Stellenbosch.

WENTZEL, D., 1982. Alkalinization of grain for high energy feeding of cold-stressed Angora goats. Proc. 3rd Int. Conf. Goat Prod. & Disease, Tucson, Arizona.

WENTZEL, D., 1983. Increasing mohair quality and production in South Africa. Proc 1983 Ranchers Roundup, San Angelo, Texas,

WENTZEL, D. & BOTHA, L.J.J., 1976. Steroid function in nutritionally stressed pregnant Angora goat does. Agroanimalia 8, 163.

WENTZEL, D., LE ROUX, MARITA M. & BOTHA, L.J.J., 1976. Effect of the level of nutrition on blood glucose concentration and reproductive performance of Angora goats. Agroanimalia 8, 59.

WENTZEL, D., MORGENTHAL, J.C., VAN NIEKERK, C.H. & ROELOFSE, C.S., 1974. The habitually aborting Angora doe. II. The effect of an energy deficiency on the incidence of abortion. Agroanimalia 6, 129.

WENTZEL, D., VILJOEN, K.S. & BOTHA, L.J.J., 1979. Physiological and endocrinological reactions to cold stress in the Angora goat. Agroanimalia II, 19.

 

Published

Karoo Agric 3 (7), 23-26