New Zealand Journal of Agricultural Research abstracts
Single trait selection for yearling fleece weight or liveweight in Romney
sheep--correlated responses in liveweight, fleece traits, and ewe
reproduction
C. A. MORRIS
D. L. JOHNSON1
R. M. W. SUMNER2
G. K. HIGHT3
J. L. DOBBIE
K. R. JONES
A. L. WRIGGLESWORTH
S. M. HICKEY
AgResearch
Ruakura Agricultural Research Centre
Private Bag 3123
Hamilton, New Zealand
1Present address: New Zealand Dairy Board, Private Bag 3016,
Hamilton, New Zealand.
2AgResearch, Whatawhata Research Centre, Private Bag 3089, Hamilton,
New Zealand
3Deceased
Abstract An experiment was carried out to study direct and
indirect responses to selection in Romney sheep. There were two selection
lines, one selected for greasy fleece weight (GFW) and the other for liveweight
(LW), maintained alongside a control line (CO). Data from lambs born in 1967-90
were analysed to quantify the correlated responses to selection. By 1990, there
had been an average of nine generations of selection with an average generation
interval of 2.7 years. The correlated responses analysed included yearling and
ewe greasy and clean fleece weights, washing yield, yearling and ewe fleece
quality traits (staple length, mean fibre diameter, fibre diameter variation,
loose wool bulk, Commission Internationale de l'Eclairange (CIE) Y value
(brightness) and CIE Y-Z value (yellowness)), birth weight, weaning weight,
yearling liveweight, ewe pre-mating weight, and ewe reproductive rate
(fertility, litter size, weaning percentage, and lamb survival). Correlated
responses were estimated as the deviation of selection lines from the CO line,
and genetic correlations were obtained by restricted maximum likelihood
techniques. Direct responses measured in the GFW and LW yearlings were 1.7 and
1.2% per year, respectively. Correlated annual responses were 0.7% in yearling
liveweight in the GFW line and 0.2% in yearling fleece weight in the LW line.
Corresponding annual changes in ewe performance were 1.5% in greasy fleece
weight and 0.5% in pre-mating weight in the GFW line, and 0.0 and 1.2%
respectively in the LW line. Mean fibre diameter increased in yearlings and
ewes of the GFW line, but did not change in the LW line. There were small but
significant increases in staple length in both lines. Loose wool bulk among GFW
yearlings was reduced by 0.12% per year but did not change significantly in
ewes. Yearlings and ewes of the LW line both showed an increase in bulk (0.15
and 0.43%, respectively). Relative to the CO flock, CIE Y-Z among yearlings
increased significantly by 1.35% per annum and 0.25% per annum in the GFW and
LW flocks respectively. Among ewes it increased in the GFW line whereas the
opposite occurred in the LW line. There was no significant change in percentage
ewes lambing as a result of GFW or LW selection. Litter size increased and lamb
survival to weaning decreased significantly, but there was a net increase per
year in lambs weaned per ewe lambing (0.27% per year for the GFW line and 0.48%
per year for the LW line).
Keywords sheep; correlated response; fleece weight;
heritability; body weight
New Zealand Journal of Agricultural Research, 1996, Vol. 39: 95-106
0028-8233/96/3901-0095 $2.50/0 (c) The Royal Society of New Zealand
1996
PDF file of entire paper: medium quality (796K); (scanned from paper original: notes about this process)
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