Last update: April 3, 2012 08:46:20 AM E-mail Print

 

Influence of cold on the Angora Goat

D Wentzel 

 

THE incidence of losses among Angora goats during periodic cold spells is surely one of the most important problems facing the Angora goat farmer. During 1977 these farmers again experienced considerable animal losses. Considering the economic value of Angora goats these deaths resulted in a considerable loss for the industry, and the country as well.

In the light of the foregoing an investigation of the problem was undertaken to determine the basic causes of such losses. For this purpose mature pregnant and young (two-tooth) shorn Angora does were subjected to cold, wet and windy conditions. The latter was created by using a cold storage chamber (0-5°C) and fans, and the animals were also wet at half hour intervals.

During the experimental period all animals received ad lib a ration containing 90% milled lucerne and 10% maize meal. Blood samples, rectal temperature and heart rate of animals were taken every four hours, and another blood sample when the animal collapsed. When an animal collapsed it was transferred to a relatively warm room, and 100 ml of an isotonic glucose solution was administered intravenously. For purposes of comparison a control group was kept under natural conditions in a pen outside the building where the experiment was conducted. Due to the fact that relatively small groups of animals (5 per group) had to be used, the results of young animals only, are presented in the graphs.

Blood glucose concentration was determined by means of an automatic analyser. The hormones, cortisol and thyroxine, were determined by techniques employing radioactive nuclei.

According to the results mature pregnant animals withstood the cold much better than the young animals. Forty per cent of the former endured the cold treatment for a period of 48 hours. In addition the first animal to collapse in this group, did so after 12 hours of cold treatment. In the case of young animals the first one collapsed after only four hours, while all had collapsed after 12 hours of cold treatment.

Changes in the rectal temperature of the experimental animals are presented graphically in Fig. 1. The rectal temperature of the control group and animals which withstood the cold stress of the 48 hour experimental period, remained relatively constant at approximately 38,9°C. In the case of animals, which collapsed during the experimental period, the rectal temperature decreased to approximately 34°C at the former stage. The decrease in body temperature, however, was much faster in the case of young animals when compared to the mature does.

 

 

According to the results related to heart rate animals subjected to the cold treatment initially showed an elevated heart rate. At the stage of collapse the heart rate was apparently subnormal. Animals, which endured the experimental period, maintained a higher heart rate throughout the experiment.

The blood glucose concentration of the experimental group showed an initial increase from 47 mg% to 82 mg%. Thereafter it decreased rapidly to a minimum of 22 mg% at the point of collapse. Following intravenous administration of glucose, the blood glucose concentration was raised to approximately 110 mg%.

According to Figures 4 and 5 it is clear that both cortisol and thyroxine showed a remarkable increase after commencing the cold treatment. Although cortisol remained at a high level, thyroxine rapidly decreased after the initial increase. It was also apparent that mature pregnant animals, which endured the experimental period, maintained a considerable high thyroxine level (approximately 17 ng/ml) throughout the experiment.

According to Figures 2 and 3 it is clear that both cortisol that cold stress results in considerable physiological and endocrinological changes in the Angora goat. Although the limited results of this experiment do not permit definite conclusions, it seems reasonable to assume that the primary cause of these losses is due to an energy deficiency resulting from a decrease in the blood glucose concentration. The latter condition, together with the low ambient temperature subsequently causes a drop in body temperature and subnormal heart function. In this respect it also appears that the Angora goat is very sensitive to stress conditions in general and that the blood glucose concentration of these animals is easily influenced by such conditions. It has already been shown that a nutritional stress causes a drop of approximately 28% in the blood glucose concentration of Angora goats. It is also noteworthy that the blood glucose concentration of some of these animals had decreased by 65%.

 

 

Contrary to the situation that nutritional stress has no influence on the cortisol level and only a slight influence on the thyroxine level of pregnant Angora goats, cold stress caused a remarkable increase in the level of both these hormones. The latter can be regarded as a natural response of the animals body to cold stress in order to increase its rate of metabolism and thus also of its energy supply to maintain normal body temperature. In this respect it is of some interest to mention that those animals, which endured the experimental period, maintained the highest level of thyroid function throughout the experiment.

 

 

As a matter of interest it should be mentioned that none of the animals, which collapsed during the experiment and subsequently, received an intravenous administration of glucose, died from the cold stress. Within approximately four hours after this treatment these animals had recovered to such an extent that they could get up, and after about 12 hours no differences could be observed between these and the animals of the control group. It is apparent that extensive research of the reaction of Angora goats to stress conditions is necessary before any recommendations for treatment of such animals in practice will be possible. The results of this investigation, however, offer a basis for future research of this aspect.

 

Published

Angora Goat and Mohair Journal 20 (2)