Infestation with the sheep body louse (Bovicola ovis) in Merino lines divergently selected for maternal multiple rearing ability.
Data were obtained from a population consisting of 160 Merino ewes, as well as 64 male and 75 female progeny of these ewes at the 2-tooth age. The age and sex groups were maintained in separate flocks. The population has been divergently selected from the same base since 1986, either for (high or H line) or against (low or L line) maternal multiple rearing ability. All animals were inspected for sheep lice (Bovicola ovis) during September/October 2002 after a wool growth period of at least 4 months. When expressed relative to mean L-line performance, the advantage in lambs weaned per ewe during the lambing season amounted to approximately 110% in the H line (1.01 vs 0.48; P < 0.01). The proportion of animals on which 1 or more lice were observed were markedly lower in 2-tooth replacement ewes than in replacement rams and mature breeding ewes (0.053 vs 0.625 and 0.531, respectively; P < 0.01). One or more lice were observed on a lower proportion of H-line ewes than on those of the L line (0.413 vs 0.571, respectively; P < 0.10), while a similar tendency was observed in 2-tooth ewe hoggets (0.033 vs 0.143, respectively; P = 0.16). When the mean number of lice on individuals on which 1 or more lice were observed was compared between lines, the average number of lice observed on H-line young rams was lower than in the L line (4.36 +/- 0.85 vs 9.71 +/- 1.84 lice, respectively; P < 0.01). A similar tendency was observed in mature breeding ewes (2.15 +/- 0.38 vs 3.22 +/- 0.42 lice, respectively; P < 0.20). The more highly reproductive H-line ewes were not more susceptible to infestation with B. ovis than ewes of the L line. In fact, available evidence suggest that H-line animals could be more tolerant of B. ovis than those of the L line.
Cloete
S W P
SW
Elsenburg Agricultural Centre, Private Bag X1, Elsenburg 7607, South Africa. schalkc@elsenburg.com
Laubscher
J M
JM
Cloete
J J E
JJ
D000818:Animals; D001947:Breeding; D005260:Female; D020022:Genetic Predisposition to Disease; D010373:Lice Infestations / Q000453:epidemiology / Q000235:genetics / Q000662:veterinary*; D008297:Male; D008003:Phthiraptera; D012641:Selection, Genetic; D012756:Sheep / Q000235:genetics*; D012757:Sheep Diseases / Q000235:genetics* / Q000469:parasitology; D014935:Wool