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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
agricultural and biological sciences
Continued selection of Romney sheep for resistance or susceptibility to nematode infection: Estimates of direct and correlated responses
Animal Science, Volume 70, No. 1, Year 2000
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Description
Divergent breeding lines of Romney sheep, selected as lambs for consistently high or low faecal worm egg count (FEC) following natural multi-species challenge by nematode parasites, were established in New Zealand at Wallaceville Animal Research Centre in 1979 and at Rotomahana Station in 1985. In 1988 the Rotomahana lines, including an unselected control line maintained under the same management conditions, were transferred to Tokanui Station where they remained for 4 years. In 1993 elite high and low FEC animals from Tokanui, along with the controls, were transferred to Wallaceville, where merged lines have since been managed together. Selection responses from the lines at Rotomahana and Tokanui, and from a further 5 years of divergent selection in the merged lines, are reported here. For the two most recent lamb crops (1996 and 1997 birth years), log-transformed FECs of the high and low lines were 1.27 and -1.46 phenotypic standard deviation units from the control. After back-transformation to the original scale, where the FEC for control line lambs averaged 1255 eggs per g, the means for the high and low lines were 3.05 and 0.27 times the control mean. Animal-model restricted maximum likelihood estimates of heritability and repeatability for single-record FEC (following separate infections) were 0.28 (s.e. 0.02) and 0.42 (s.e. 0.01), respectively. Correlated responses in production traits include significantly decreased post-weaning weight gain and increased dags (breech soiling) in lambs, and decreased fleece weight in yearlings and ewes in the low FEC line, compared with those in the high line. However the low FEC line had proportionally 0.11 more lambs weaned per ewe mated than the high FEC line (P < 0.01). It is concluded firstly that selection for high or low FEC in Romneys has achieved an 11-fold difference between the divergent lines. Secondly, it will generally be necessary in a commercial environment to apply index selection for a combination of increased productivity, decreased FEC and possibly decreased dags, when potential candidates are recorded under conditions of nematode challenge. © 2000 British Society of Animal Science.
Authors & Co-Authors
Morris, Chris A.
New Zealand, Hamilton
Agresearch Ruakura
Vlassoff, Alex
New Zealand, Lincoln
Agresearch
Bisset, Stewart A.
New Zealand, Lincoln
Agresearch
Baker, Robert Leyden
New Zealand, Hamilton
Agresearch Ruakura
Kenya, Nairobi
International Livestock Research Institute Nairobi
Watson, H. T.G.
New Zealand, Hamilton
Agresearch Ruakura
United States, New York
Pfizer Inc.
West, Christopher J.
New Zealand, Lincoln
Agresearch
Wheeler, Mary
New Zealand, Hamilton
Agresearch Ruakura
Statistics
Citations: 118
Authors: 7
Affiliations: 4
Identifiers
Doi:
10.1017/S1357729800051560
ISSN:
13577298