Response to partial selection for fecundity in Merino sheep

1978 ◽  
Vol 18 (94) ◽  
pp. 635 ◽  
Author(s):  
TLJ Mann ◽  
DE Taplin ◽  
RE Brady
Keyword(s):  
Analysis Of Variance ◽  
Selection Pressure ◽  
Age Groups ◽  
South Australia ◽  
Realized Heritability ◽  
Merino Sheep ◽  
Agricultural College ◽  
Selection For ◽  
Pass Through ◽  
Australian Merino

Divergent selection for fecundity in a South Australian Merino flock was carried out over a 10 year period at Roseworthy Agricultural College, South Australia. Comparisons were made between two flocks of sheep in which selection was restricted to ram replacements. Analyses showed that very little response was achieved. Pooled estimates of repeatability by analysis of variance were 0.04 for lambs born per ewe joined (LBJ) and 0.14 for lambs born per ewe lambing (LBP). Pooled half-sib estimates of heritability were 0,10 for LBJ and 0.10 for LBP. The realized heritability of LBP was 0.03, averaged over age groups. The lack of response was due to limited selection pressure and the time taken for improvement to pass through the breeding flock.

Corrigendum - Response to partial selection on clean fleece weight in South Australian strong-wool Merino sheep

1969 ◽  
Vol 20 (1) ◽  
pp. 151
Author(s):  
O Mayo ◽  
JC Potter ◽  
RE Brady ◽  
CW Hooper
Keyword(s):  
Fibre Diameter ◽  
Index Method ◽  
Visual Method ◽  
Merino Sheep ◽  
Index Group ◽  
Agricultural College ◽  
Selection For ◽  
The Difference ◽  
Fleece Weight ◽  
Selection Of

This paper reports the results of an experiment carried out at Roseworthy Agricultural College from 1953 to 1966 comparing two bases of selection of rams: (1) visual appraisal (the "visual" method); (2) visual culling of 70% of rams followed by selection of breeding animals from the remaining 30% on the basis of clean fleece weight (the "index" method). No selection for fleece weight was practiced on ewes. Seven rams were used in each of the two flocks, and six of the seven were replaced each year by 16-month-old animals from the succeeding drop, the seventh being a year older. Rams used for breeding in the Index flock were significantly higher in clean fleece weight than those of the Visual flock, and were higher, though not always significantly so, in greasy fleece weight. This led to a divergence between the flocks for clean fleece weight (P < 0.05), with an increase of c. 0.05 lb per year per head for the Index animals over the Visual animals. The Index rams were more wrinkly and lighter, on the whole, than the Visual rams, and the wrinkly effect carried over into their offspring with a slight divergence apparent, the Index animals becoming more wrinkled than the Visual (P < 0.05). In fibre diameter there were no differences between selected animals or between flocks. Visual rams tended to have more crimps per inch in their wool, and this was observed in the flocks also, but the divergence was not significant (P > 0.05). Index rams had longer wool than Visual rams, with the difference generally significant within years, and this tendency carried over in a lesser manner to the flocks. Fleece density was generally greater in the Index group, though not usually significantly so. This experiment did not include a randomly bred control flock, but was rather designed to compare two practical methods of selecting rams. Merits of this scheme are discussed in the light of both groups' failure to show increases in fleece weight over the course of the experiment

Selection for economic characters in Australian Merino sheep.

1954 ◽  
Vol 5 (2) ◽  
pp. 305 ◽  
Author(s):  
FHW Morley
Keyword(s):  
Body Weight ◽  
Least Squares ◽  
Expected Value ◽  
Merino Sheep ◽  
Random Deviation ◽  
Selection For ◽  
Australian Merino ◽  
Coefficient Of Inbreeding ◽  
Staple Length

The effect of inbreeding and parent-offspring regressions for some economic characters of Merino sheep were estimated by a least-squares procedure. The model was: Yi = a + b1X1i + b2X2i + ei ,where Yi and X1i represent the phenotype and coefficient of inbreeding of the ith sheep, X2i the phenotype of the dam of that sheep, and ei the random deviation of Y, from its expected value. Increased coefficients of inbreeding were accompanied by highly significant decreases in greasy and clean fleece weights, body weight, and fold score. No significant association was observed between inbreeding and yield, staple length, crimps per inch, or birthcoat grading. Increased inbreeding was associated with decreased survival. Significant correlations between X1 and X2 were demonstrated for fleece weights, staple length, body weight, and crimps per inch. The implications of these correlations are discussed. The parent-offspring regressions were all highly significant. Estimates of heritability were high for all characters studied. The importance of these findings on the effectiveness of selection for flock improvement is considered.

Genetic studies of South Australian Merino sheep. 4. Genetic, phenotypic and environmental correlations between various wool and body traits

1982 ◽  
Vol 33 (2) ◽  
pp. 363 ◽  
Author(s):  
IP Gregory
Keyword(s):  
Great Increase ◽  
Fibre Diameter ◽  
Skin Thickness ◽  
Primary Follicle ◽  
Genetic Studies ◽  
Environmental Correlations ◽  
Merino Sheep ◽  
Selection For ◽  
Fleece Weight ◽  
Australian Merino

Genetic, phenotypic and environmental correlations were estimated between 23 quantitative and qualitative wool and body traits of South Australian Merino sheep. Clean fleece weight was significantly correlated genetically with greasy fleece weight (0.62), yield (0.47), staple length (0.41), crimps per inch (-0.34), secondary/primary follicle ratio (0.37) and skin thickness (0.39). No significant half-sib genetic correlation was found between clean fleece weight and fibre diameter and the dam-offspring correlation was quite low, although significant (0.16, P < 0.05). This indicates that selection for clean fleece weight should not lead to any great increase in fibre diameter. Skin thickness is discussed as a possible early indicator of clean fleece weight.

Selection for carcass length in Large White pigs

1968 ◽  
Vol 10 (4) ◽  
pp. 359-372 ◽  
Author(s):  
J. E. Duckworth ◽  
W. Holmes
Keyword(s):  
Selection Pressure ◽  
Herd Size ◽  
Litter Production ◽  
Realized Heritability ◽  
Large White ◽  
Components Of Variance ◽  
Selection Programme ◽  
Selection For ◽  
One Year ◽  
Sib Selection

A sib selection programme for length of carcass was carried out for five generations within a closed herd of Large White pigs. A generation interval of one year was obtained.Litter production was good throughout the project and the numbers of pigs born and reared in the final generation were 11·2 and 10·3 respectively.Overall response to selection was predicted with reasonable success. The increase in length was associated with an increase in number of vertebrae.Heritability for length of carcass computed from the pooled components of variance was 0·53 ± 0·12. Realized heritability was 0·5 ± 0·1. No control strain was maintained.Correlated traits moved in the expected directions and responses were beneficial for traits such as backfat measurements and chest depth, but unfavourable for belly thickness and ham conformation. Carcass acceptability was not good initially and this deteriorated during the project. The difficulties involved in maintaining selection pressure and herd size are discussed. Abnormalities and lameness were recorded and did not increase systematically over the experiment.It is suggested that the specific relationships between ‘conformation’, carcass value and viability require further investigation with particular reference to length of leg and length of carcass.

Selection schemes for improving both reproduction rate and clean wool weight in the Australian Merino under field conditions

1965 ◽  
Vol 16 (5) ◽  
pp. 863 ◽  
Author(s):  
SY Young ◽  
Turner H Newton
Keyword(s):  
Theoretical Consideration ◽  
Relative Efficiency ◽  
Selection Pressure ◽  
Field Conditions ◽  
Reproduction Rate ◽  
Optimal Method ◽  
Merino Sheep ◽  
Selection Of ◽  
Australian Merino

Theoretical consideration has been given to 28 selection schemes which might readily be applied for the improvement of both number of lambs born and clean wool weight per head in Australian Merino sheep under field conditions. Two sets of relative weights were used, one lamb being considered equivalent to 5 or 10 lb of clean wool, and when both characters were selected in one sex, equal selection pressure was applied to each. Quality of wool is assumed to be safeguarded by preliminary culling of off-types. The schemes were investigated at two levels of twinning (15 and 30%). At both levels, the optimal method of ram selection was to select on clean wool weight among twin-born rams. At the lower level, the optimal method of ewe selection was to save twin-born ewes and to make up numbers by selecting on clean wool weight among those born as singles. At the higher level, this scheme was slightly exceeded in total genetic gain by one involving selection of ewes on their own 3-year-old reproduction rate. After 10 years of selection under the optimal scheme, an increase of about 40 lambs born per 100 ewes joined would be expected in reproduction rate, and about 1.2 lb clean wool in the cut per head. The gain in wool weight will be less (about 1 lb) if more rigorous culling on crimp is practiced, but the relative efficiency of the schemes near the optimum will not be changed. The tables presented could be used in flocks of any breed in which clean wool weight and reproduction rate were uncorrelated and to which approximately the same estimates of heritability, variances, and relative weights of lamb and wool could be applied.

Selection for economic characters in Australian Merino sheep. VI. Inheritance and interrelationships of some subjectively graded characteristics

1955 ◽  
Vol 6 (6) ◽  
pp. 873 ◽  
Author(s):  
FHW Morley
Keyword(s):  
Genetic Correlation ◽  
Reproductive Efficiency ◽  
Agricultural Experiment Station ◽  
Merino Sheep ◽  
Experiment Station ◽  
Agricultural Experiment ◽  
Selection For ◽  
Fleece Weight ◽  
Australian Merino

Genetic and phenotypic relationships among subjectively graded characteristics were examined in a flock of Merino sheep a t Trangie Agricultural Experiment Station. Estimates of heritability were: wool handle, 0.30; wool colour, 0.63; wool character, 0.38; back wool, 0.00; hocks, 0.14; face cover, 0.38. The genetic correlation between face cover and fleece weights suggested that selection for fleece weight would increase "wool-blindness", with possible diminution of reproductive efficiency. Selection for wools of good character (well-defined crimp) would improve softness and would not decrease fleece weight. The conclusion emerging from this and previous studies is that intense selection for high fleece weight will be rewarded by substantial increases, and will be offset only partly by adverse changes in a few of the several characters investigated.

Response to partial selection on clean fleece weight in South Australian strong-wool Merino sheep

1969 ◽  
Vol 20 (1) ◽  
pp. 151
Author(s):  
O Mayo ◽  
JC Potter ◽  
RE Brady ◽  
CW Hooper
Keyword(s):  
Fibre Diameter ◽  
Index Method ◽  
Visual Method ◽  
Merino Sheep ◽  
Index Group ◽  
Agricultural College ◽  
Selection For ◽  
The Difference ◽  
Fleece Weight ◽  
Selection Of

This paper reports the results of an experiment carried out at Roseworthy Agricultural College from 1953 to 1966 comparing two bases of selection of rams: (1) visual appraisal (the "visual" method); (2) visual culling of 70% of rams followed by selection of breeding animals from the remaining 30% on the basis of clean fleece weight (the "index" method). No selection for fleece weight was practiced on ewes. Seven rams were used in each of the two flocks, and six of the seven were replaced each year by 16-month-old animals from the succeeding drop, the seventh being a year older. Rams used for breeding in the Index flock were significantly higher in clean fleece weight than those of the Visual flock, and were higher, though not always significantly so, in greasy fleece weight. This led to a divergence between the flocks for clean fleece weight (P < 0.05), with an increase of c. 0.05 lb per year per head for the Index animals over the Visual animals. The Index rams were more wrinkly and lighter, on the whole, than the Visual rams, and the wrinkly effect carried over into their offspring with a slight divergence apparent, the Index animals becoming more wrinkled than the Visual (P < 0.05). In fibre diameter there were no differences between selected animals or between flocks. Visual rams tended to have more crimps per inch in their wool, and this was observed in the flocks also, but the divergence was not significant (P > 0.05). Index rams had longer wool than Visual rams, with the difference generally significant within years, and this tendency carried over in a lesser manner to the flocks. Fleece density was generally greater in the Index group, though not usually significantly so. This experiment did not include a randomly bred control flock, but was rather designed to compare two practical methods of selecting rams. Merits of this scheme are discussed in the light of both groups' failure to show increases in fleece weight over the course of the experiment

Across population genetic parameters for wool, growth, and reproduction traits in Australian Merino sheep. 1. Data structure and non-genetic effects

2007 ◽  
Vol 58 (2) ◽  
pp. 169 ◽  
Author(s):  
E. Safari ◽  
N. M. Fogarty ◽  
A. R. Gilmour ◽  
K. D. Atkins ◽  
S. I. Mortimer ◽  
...  
Keyword(s):  
Genetic Parameters ◽  
Age Groups ◽  
Genetic Effects ◽  
Production Traits ◽  
Merino Sheep ◽  
Wool Growth ◽  
Reproduction Traits ◽  
Fleece Weight ◽  
Growth And Reproduction ◽  
Australian Merino

Accurate estimates of adjustment factors for systematic environmental effects are required for genetic evaluation systems. This study combined data from 7 research resource flocks across Australia to estimate genetic parameters and investigate the significance of various environmental factors for production traits in Australian Merino sheep. The flocks were maintained for several generations and represented contemporary Australian Merino fine, medium, and broad wool bloodlines over the past 30 years. Over 110 000 records were available for analysis for each of the major wool traits, with over 2700 sires and 25 000 dams. Univariate linear mixed animal models were used to analyse 6 wool, 4 growth, and 4 reproduction traits. This first paper outlines the data structure and the non-genetic effects of age of the animal, age of dam, birth-rearing type, sex, flock, bloodline, and year, which were significant with few exceptions for all production traits. Age of dam was not significant for reproduction traits and fleece yield. Generally, wool, growth, and reproduction traits need to be adjusted for age, birth-rearing type, and age of dam before the estimation of breeding values for pragmatic and operational reasons. Adjustment for animal age in wool traits needs to be applied for clean fleece weight (CFW), greasy fleece weight (GFW), and fibre diameter (FD) with inclusion of 2 age groups (2 years old and >2 years old), but for reproduction traits, inclusion of all age groups is more appropriate. For GFW, CFW, and hogget weight (HWT), adjustment for only 2 dam age groups of maiden and mature ewes seems sufficient, whereas for birth (BWT), weaning (WWT), and yearling (YWT) weights, adjustments need to be applied for all dam age groups. Adjustment for birth-rearing type (single-single, multiple-single, multiple-multiple) is appropriate for wool, growth, and reproduction traits. The implications of adjustment for non-genetic effects are discussed.

Selection for economic characters in Australian Merino sheep. II. Relative efficiency of certain aids to selection.

1952 ◽  
Vol 3 (4) ◽  
pp. 409 ◽  
Author(s):  
FHW Morley
Keyword(s):  
Artificial Insemination ◽  
Relative Efficiency ◽  
Mass Selection ◽  
Progeny Testing ◽  
Merino Sheep ◽  
Selection For ◽  
The Cost ◽  
Australian Merino

Theoretical consequences of the use of progeny testing, sib testing, and mass selection are examined in a flock of 1,000 ewes producing 700 progeny of breeding age each year. Selection based on a combination of individual merit and merit of half-sibs should result in approximately the same annual improvement as that achieved by optimum use of progeny-tested sires. In large flocks extensive use of outstanding sires by artificial insemination may increase progress for traits with heritability of about 0.3 by a factor of about 1.2 as compared with mass selection. The advantages to be gained by progeny testing and artificial insemination may be outweighed by the dangers of inbreeding, and the cost involved would have to be considered. As most of these advantages should be achieved by combination or even by mass selection, which avoid inbreeding and much of the cost, progeny testing with wide use of progeny-tested sires is unlikely to be the most economical road to flock improvement.

Genetic and phenotypic parameters for body weight and greasy fleece weight at weaning in Australian Merino sheep

1965 ◽  
Vol 16 (6) ◽  
pp. 997 ◽  
Author(s):  
SSY Young ◽  
GH Brown ◽  
Turner H Newton ◽  
CHS Dolling
Keyword(s):  
Body Weight ◽  
Genetic Correlations ◽  
Indirect Selection ◽  
Mass Selection ◽  
Sampling Errors ◽  
Merino Sheep ◽  
Selection For ◽  
Fleece Weight ◽  
Positive Correlations ◽  
Australian Merino

Genetic and phenotypic parameters for body weight and greasy fleece weight at weaning were estimated in a flock of Australian Merinos. Maternal handicaps were found to be more severe at weaning than at the older age of 15–16 months. Lambs born to 2-year-old ewes were 2–3 lb lighter in body weight at weaning and 0.2 lb lighter in greasy fleece weight than the offspring of adult ewes. Twin lambs were on the average 6–7 lb lighter than singles and cut 0.5 lb less greasy wool. Greasy fleece weight at weaning was found to be fairly highly heritable but only moderately repeatable. The repeatability and heritability of weaning body weight were both low. The genetic correlations estimated here were associated with appreciable sampling errors, but the estimates strongly suggested high and positive correlations between measurements at weaning and at 15–16 months for both traits. A general consideration of the relative efficiency of direct versus indirect selection, based on the information obtained in this study, leads to the conclusion that for greater genetic gains, mass selection for greasy wool weight and body weight at weaning should be carried out on measurements at 15–16 months of age, rather than at weaning.

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