Last update: November 24, 2010 02:03:13 PM E-mail Print

 

HAEMOGLOBIN POLYMORPHISM IN FOUR SHEEP BREEDS

 

M.J. Herselman, MA Snyman and BR King

Grootfontein ADI, Private Bag X529, Middelburg, 5900

 


Conflicting evidence exists concerning the relationships between genetically controlled red blood cell characteristics and measures of adaptation and productivity in sheep. However, from literature the following three points of interest appear to be substantiated: i) A relationship between erythrocyte potassium concentration (and potassium types) and wool quality and quantity exists, ii) Sheep carrying the HbA gene is superior with respect to resistance to Haemonchus contortus iii) Haemoglobin type is associated with production and reproduction rate in particular environments. This study was conducted to shed more light on the latter with regard to South African sheep breeds. Breeding ewes, rams and offspring of the Grootfontein Merino stud (Merino),  Cradock fine wool Merino stud (Finewool),  Carnarvon Afrino flock (Afrino), Carnarvon Dorpers flock (Dorper)  and the Carnarvon Namaqua Afrikaner flock (Namaqua) were used in this study. One blood sample per animal was collected by venipuncture into heparinized vacuum tubes after overnight starvation. Haematocrit was measured by means of micro-centrifugation on an aliquot of this blood sample. For determination of haemoglobin type, the blood sample was centrifuged at 2800 G for 30 minutes, plasma was aspirated off and 0.1 ml of erythrocytes was haemolysed with 0.5 ml distilled water to release the haemoglobin. Haemoglobin type was determined by electrophoresis on cellulose acetate plates in a horizontal bath for 25 minutes at 230 Volts.  Production parameters that were collected in the different flocks were also used in the analysis. Differences in gene frequency between flocks were tested by Chi-square procedures. Differences in production parameters between different erythrocyte genotypes were   tested for significance by the GLM procedure of SAS.  The gene frequency for HbA was 0.363, 0.109, 0.320, 0.083 and 0.407 for the Afrino, Dorper, Finewool, Namaqua and Merino flocks respectively. It would seem that the HbA gene occurs more frequently among wool producing sheep when compared to mutton sheep. Body weight at 42 days and at 18 months differed significantly between different haemoglobin types, although these differences were relatively small. In wool sheep, staple length and certain wool quality traits also differed among different haemoglobin types. In the Finewool flock, the number of lambs weaned per ewe mated was 1.32, 1.12 and 1.17 for the AA, AB and BB haemoglobin types respectively. No definite conclusion as to the influence of haemoglobin type on the performance of different sheep breeds can be made from this study. However, the growth and reproductive performance of sheep in the Finewool flock with haemoglobin type AA were higher than that of the other haemoglobin types.