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HAEMATOCRIT IN ANGORA GOATS, BOER GOATS AND MERINO SHEEP

MJ Herselman

Grootfontein ADI, Private Bag X529, Middelburg, 5900

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INTRODUCTION

It is generally accepted that the Angora goat is the most efficient fibre producing small stock breed. Unfortunately, the Angora goat is also known to have several specific problems, most of which have been investigated to some extend. One of the major problems experienced in practice is the low reproduction rate, especially in young does. This low reproduction rate results from low conception rates, abortions and a relatively high kid mortality rate10. Following extensive investigations into the abortion problem, it was concluded that the endocrine pathway, through which abortions induced by nutritional stress are mediated, originates from a drop in maternal blood glucose concentration11,12. Frequent and severe losses of Angora goats during cold spells, especially among newly shorn animals, also present a serious problem to mohair producers. Research results showed that an abrupt drop in blood glucose concentration, associated with collapse of the cold stressed animal, was the crucial factor leading to the failure of the mechanism responsible for the required rate of metabolic heat production12.

The initial finding of some disorder in glucose metabolism of Angora goats was followed by several investigations into hormonal aspects of high vs. low fibre producing animals at Grootfontein4,5. During most of these experiments it was noticed that, after centrifugation, blood of Angora goats had less cells and more plasma. It was therefore decided to include haematocrit determination as a standard procedure in all subsequent projects. Although no attempt is made to attach any physiological significance to this phenomenum, the aim of this paper is to report on the results obtained, until now, on haematocrit of different small stock breeds.

EXPERIMENTAL PROCEDURES

In Experiment 1, 24 female Angora goats, Boer goats and Merino sheep (8 per breed) were used. All animals were 4 months of age. Two weeks were allowed for animals to adapt to a lucerne diet before a blood sample was taken from each animal. In Experiment 2 adult Angora goat, Boer goat and Merino ewes (8 per breed) were used. Prior to the first blood sample being taken, ewes had ad libitum access to milled lucerne hay for 49 days. This was followed by a period of 42 days through which blood samples were taken at regular intervals. During this period animals also received milled lucerne, except from day 21 to day 28 during which period animals were starved and only received drinking water.

All blood samples were collected by venipuncture from the right jugular vein into 10 ml heparinized and evacuated glass blood collection tubes (Radem Laboratory Supplies (Pty) Ltd, Santon. S.A.). Haematocrit was determined after centrifugation (2500 x g; 4 EC; 20 min).

All statistical analyses were performed using the GLM procedures of SAS6. Data of Experiment 2 were analysed as a split-plot, repeated measures design. The model statement included breed and day. The breed effect was tested using animal within breed as error term. Least square means were separated using the PDIFF option of SAS6.

RESULTS & DISCUSSION

Haematocrit values recorded in Experiment 1 differed (P < 0.05) among all three breeds and were 32.1 ± 1.29, 35.5 ± 0.82 and 44.7 ± 0.90 % for the Angora, Boer goat and Merino, respectively. As haematocrit is an indirect measure of iron balance, these figures would suggest relative large differences in iron status among these breeds. As these blood samples were taken soon after weaning and the fact that milk has a low iron content, it is possible that differences in milk and feed intake among the breeds during the pre-weaning period could have contributed to these differences in iron status. Although all animals were of similar age, body weight of the respective breeds were 17.2, 19.7 and 25.1 kg. As it is known that haematocrit changes with age7 it is also possible that part of the differences recorded in Experiment 1 can be explained by differences in physiological age.

The results obtained in Experiment 2 are depicted in Figure 1.

 

Figure 1 Packed cell volume (%) in adult Angora , Boer goat and Merino ewes

Haematocrit differed among breeds (P<0.0001) and were 31.8, 40.2 and 44.9 % (SE=1.87) for Angora, Boer goat and Merino ewes respectively. Day of sampling had a significant (P<0.0001) effect on haematocrit due to the 7 day starvation period. The breed x day interaction was also significant (P<0.001) due to haematocrit of Merino ewes being less influenced by starvation when compared to that of goats. The haematocrit values obtained in Experiment 2 is in close accordance with that obtained in Experiment 1. The haematocrit of Boer goats were, however, somewhat higher in adult compared to young animals. In Experiment 2, no age or dietary influences on haematocrit could have been expected as all animals were more than 4 years old and were fed the same diet for seven weeks prior to the first blood sample being collected.

Haematocrit in sheep has been shown to be associated with haemoglobin type. In this regard, haematocrit levels of 44.0, 39.4 and 34.8% have been reported in sheep of haemoglobin types A, AB and B respectively8. Haemoglobin type has also been associated with respect to resistance to Haemonchus contortus and with fertility in particular environments1. It has also been reported that differences in haematocrit in sheep with different haemoglobin types contribute to differences in whole blood potassium concentration 2,3,8 and that fibre production characteristics such as medullated fibres and fibre diameter is significantly related to potassium concentration in the erythrocytes 9. From the preliminary results on haematocrit and the foregoing discussion, it seems necessary to continue with haematological investigation of Angora goats to provide further information on the underlying causes of its unique productive and reproductive problems.

CONCLUSION

Haematocrit in young and adult Angora goats were found to be considerably lower than that of Boer goats and Merino sheep. Although no definite conclusion on the reason for these differences in haematocrit can be drawn, from literature it would seem necessary that this aspect should be studied in more detail to provide more information on the numerous problems experienced in Angora goats.

REFERENCES

1. 1 AGAR, N.S., EVANS, J.V. & ROBERTS, J., 1972. Red blood cell potassium and haemoglobin polymorphism in sheep. A review. Anim. Breed. Abstr., 40, 407.

2. EVANS, J.V., KING, J.W., COHEN, J.W.B., HARRIS, B.L. & WARREN, F.L., 1956. Genetics of haemoglobin and blood potassium differences in sheep. Nature, Lond., 178, 849.

3. FECHTER, H. & MYBURGH, S.J., 1967. Haemoglobin and potassium types in South African sheep breeds. Proc. 10th Eur. Conf. Anim. Blood Grps Biochem. Polymorph., Paris, 1966, 395.

4. HERSELMAN, M.J. & VAN LOGGERENBERG A.A., 1997. Studies on small ruminant breeds with inherent differences in fibre production and hardiness. III. Effect of age and intravenous injections of insulin and corticotrophin releasing factor on plasma cortisol concentration. S. Afr. J. Anim. Sci. (Submitted)

5. HERSELMAN, M.J. & VAN LOGGERENBERG A.A., 1997. Plasma concentrations of cortisol, insulin, triiodothironine, thyroxine and insulin-like growth factor-I in different breeds of small stock. Proc. S.A.S.A.S. (Submitted)

6. LITTELL, R.C., FREUD, R.J. & SPECTOR, P.C., 1991. SAS System for Linear Models, Third Edition. SAS Institute Inc., Cary, NC.

7. McGILVERY, R.W. & GOLDSTEIN, G.W., 1983. Biochemistry: A functional Approach. Igaku-Shoin/Saunders, London.

8. MOUNIB, M.S. & EVANS, J.V., 1959. The effect of potassium types and breed on dry matter percentage and specific gravity on the red blood cells and plasma of sheep. J. Agric. Sci., Camb., 53, 118.

9. TANEJA, G.C., NARAYAN, N.L. & GHOSH, P.K., 1969. On the relationship between wool quality and the type and concentration of blood potassium in sheep. Experientia, 25, 1200.

10 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 pregnant Angora goats. Agroanimalia 8, 59.

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

12. WENTZEL, D., VILJOEN, K.S. & BOTHA, L.J.J., 1979. Physiological and endocrinological reactions to cold stress in the Angora goat. Agroanimalia 11, 19.

 

 

Published

Proc. S.A. Soc. Anim. Prod. 35, 271