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.

MASS SELECTION FOR RESISTANCE TO SELENOPHOMA BROMIGENA IN NORTHERN AND SOUTHERN TYPES OF BROMUS INERMIS

1967 ◽  
Vol 47 (6) ◽  
pp. 679-681 ◽  
Author(s):  
J. Drew Smith ◽  
R. P. Knowles
Keyword(s):  
Disease Resistance ◽  
Leaf Spot ◽  
Bromus Inermis ◽  
Mass Selection ◽  
Progeny Testing ◽  
Smooth Bromegrass ◽  
Selection For ◽  
Better Than

In the epidemic years 1965 and 1966, field ratings confirmed that southern strains of smooth bromegrass, Bromus inermis Leyss, were generally less susceptible to leaf spot caused by Selenophoma bromigena (Sacc.) Sprague & A. G. Johnson than northern strains. The northern/southern hybrid S-6733, developed by mass selection and progeny testing, was found to resist S. bromigena at least as well as the southern strains Lincoln and Redpatch, and better than the southern Saratoga. It was found possible to improve resistance of the susceptible northern strain Carlton by mass selection. Northern strains probably do not have as great a potential for improvement in disease resistance as southern strains or hybrids.

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.

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.

Short-term Progeny Tests and Second Generation Breeding in Slash Pine

1973 ◽  
Vol 3 (2) ◽  
pp. 165-169
Author(s):  
E. C. Franklin ◽  
A. E. Squillace
Keyword(s):  
First Generation ◽  
Second Generation ◽  
Slash Pine ◽  
Mass Selection ◽  
Progeny Testing ◽  
Family Selection ◽  
Short Term ◽  
Major Disadvantage ◽  
Selection For ◽  
Almost All

Progeny testing is the most widely used method for intensive genetic evaluation of selected forest trees, but its major disadvantage is the length of time needed to get results. To circumvent this problem in selection for a multiproduct strain of slash pine (Pinuselliottii Engelm.), a system for short-term (3-year) progeny testing was developed. Oleoresin yields of selected second-generation 19-year-old parent trees were compared with yields of their 3-year-old offspring. Both parents and offspring showed little variation and a low offspring–parent correlation (r = 0.18), but other traits based on the same parent trees when they were 25 years old and their 3-year-old offspring showed relatively large amounts of variation and moderate to strong offspring-parent correlations: height, r =.56; volume, r = 0.43; turpentine, r = 0.71; ethanol–benzene extractives, r = 0.38; specific gravity, r = 0.43; moisture content, r = 0.34. Thus, indications are that additional gains could be made in the first generation by selecting among parent trees on a progeny performance basis in all traits except oleoresin yield. Original mass selection for oleoresin yield achieved gains of 100% improvement and apparently exploited almost all of the genetic variation in the base population. In second generation selection, progeny testing will be used primarily in screening for fusiform rust resistance. Between-family plus within-family selection will be used for other traits.

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 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.

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