Last update: November 19, 2010 09:26:31 AM E-mail Print


Internal parasite resistance of sheep evaluated in two different environments


M.A. Snyman1, Y. Venter2, M. van Heerden1 and T. Buys3


1Grootfontein ADI, P/Bag X529, Middelburg (EC), 5900

2Potchefstroom Livestock Centre, P/Bag X804, Potchefstroom, 2520

3Carnarvon Experimental Station, P.O. Box 98, Carnarvon, 8995

Corresponding author: Gretha Snyman


Many of the ram breeders in South Africa are located in the drier, western parts of the country, with a lower natural parasite infestation. In many instances, the progeny of these rams has to produce and reproduce in higher rainfall areas of the country, where higher natural parasite infestations prevail. It is therefore necessary to develop a protocol for the evaluation of breeding values for parasite resistance for sires bred in the extensive sheep grazing areas of South Africa where natural parasite infection is limited. A project for this purpose has therefore been undertaken. Dorper and Afrino ram lambs from the Carnarvon experimental flocks, which were progeny of sires with high and low breeding values for resistance (estimated from artificial challenge done at Carnarvon when the sires were 8 months of age), were transferred to the Potchefstroom Livestock Centre at 11 months of age and kept on pastures for 5 months. During this period, resistance of the animals to internal parasites was evaluated under natural challenge conditions. For the Dorpers, a high phenotypic correlation (0.77) was obtained between the sire’s own faecal egg count (FEC), done under artificial challenge at Carnarvon when the sire was 8 months of age, and the artificial challenge FEC of his progeny. The correlation between the sire’s artificial FEC and the natural challenge FEC of his progeny was lower, but also positive (0.37). A positive correlation (0.49) was also estimated between the artificial (done at Carnarvon) and the natural challenge (done at Potchefstroom) FEC of the ram lambs themselves. Lower correlations were estimated between the different tests for the Afrino rams than for the Dorper rams. More data are needed before accurate conclusions can be made in this regard. The results on the positive correlations between artificial challenge breeding value of sires and artificial as well as natural breeding values of their progeny are, however, promising.