Selection for economic characters in Australian Merino sheep. V. Further estimates of phenotypic and genetic parameters.

1955 ◽  
Vol 6 (1) ◽  
pp. 77 ◽  
Author(s):  
FHW Morley
Keyword(s):  
Genetic Correlations ◽  
Minor Importance ◽  
Agricultural Experiment Station ◽  
Genetic Progress ◽  
Sheep Population ◽  
Merino Sheep ◽  
Agricultural Experiment ◽  
Selection For ◽  
Fleece Weight ◽  
Genetic Homeostasis

Estimates of heritability, genetic correlations, phenotypic correlations, and other parameters among eight characteristics were obtained from Merino sheep at Trangie Agricultural Experiment Station. One set of estimates was obtained by parent-offspring regressions from data obtained between 1943 and 1952. Another set was obtained by half-sib analyses from data from sheep with first adult shearings in 1953. Estimates of heritability were: greasy fleece weight, 0.40 ± 0.06; yield (per cent.), 0.39 ± 0.07; clean fleece weight, 0.47 ± 0.07; staple length, 0.56 � 0.07; crimps per inch, 0.47 ± 0.11; folds, 0.50 ± 0.07; body weight, 0.36 ± 0.08; birthcoat, 0.80 ± 0.10. The most important genetic correlation limiting genetic improvement in clean fleece weight is that between this trait and crimps per inch. Because of this the rate of improvement in fleece weight could be reduced by about 30 per cent. whenever crimps per inch is also selected. Other genetic correlations indicate antagonisms between characteristics, but these antagonisms appear to be of minor importance except that between clean fleece weight and crimps per inch. This sheep population does not appear to have reached a state of genetic homeostasis, a t least with respect to the characteristics studied. However, the findings emphasize the necessity for careful evaluation of the economic importance of different traits, and for accurate measurement, if maximum genetic progress is to be achieved.

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.

Selection for weaning weight in Merino sheep. 2. Correlated responses in other production characters

1965 ◽  
Vol 5 (19) ◽  
pp. 361 ◽  
Author(s):  
WA Pattie
Keyword(s):  
Milk Protein ◽  
Survival Rates ◽  
Genetic Correlations ◽  
Negative Relationship ◽  
Weaning Weight ◽  
Merino Sheep ◽  
Selection For ◽  
The Difference ◽  
Fleece Weight ◽  
Lamb Growth

The heritabilities of seven production characters of Merino Sheep and their phenotypic and genetic correlations with corrected weaning weight have been calculated using half-sib and dam-daughter correlations. Realized genetic correlations calculated from responses in Weight Plus and Weight Minus selection flocks, which showed broad agreement with these correlations, were : 17-month body weight, 0.72 ; yield, 0.22 ; clean fleece weight, 0.24 ; and staple length, 0.17. There was zero relationship with greasy fleece weight and crimps per inch, and a large negative relationship between folds and high weaning weight. There were strong phenotypic correlations between lamb growth and milk production through the total weight of milk protein produced. The lamb's genotype was the most important contributor to the difference in weaning weight between the flocks. There were no differences in reproductive performance or survival rates between the flocks but twice as many twin rams and 20 per cent more twin ewes were mated in the Weight Minus flock over the selection period.

Resistance to nematode parasites in Merino sheep: correlation with production traits

1998 ◽  
Vol 49 (8) ◽  
pp. 1201 ◽  
Author(s):  
S. J. Eady ◽  
R. R. Woolaston ◽  
R. W. Ponzoni ◽  
R. P. Lewer ◽  
H. W. Raadsma ◽  
...  
Keyword(s):  
Variance Components ◽  
Genetic Correlations ◽  
Fibre Diameter ◽  
Correlated Response ◽  
Production Traits ◽  
Merino Sheep ◽  
Nematode Parasites ◽  
Faecal Egg Count ◽  
Selection For ◽  
Fleece Weight

Merino sheep representing a range of bloodlines in resource flocks located across Australia were tested for resistance to gastro-intestinal nematodes. These flocks included the JB Pye Flock (Camden, NSW), Katanning Base Flock (Katanning, WA), Turretfield Merino Resource Flock (Rosedale, SA), and the CSIRO Finewool Flock (Armidale, NSW) and included a total of 328 sire groups. Resistance to nematodes was measured by faecal egg count (FEC). Data were also available for greasy and clean fleece weight (GFW and CFW, respectively), fibre diameter (FD), and body weight (BW) at a range of ages from weaning to 21 months. Variance components were estimated by restricted maximum likelihood, fitting an animal model and estimating covariances in a series of bivariate analyses. Phenotypic correlations between FEC0·33 and production traits were all close to zero ( –0·09–0·02). Genetic correlations between FEC0·33 and production traits were –0·20, –0·18, and –0·26 for weaning weight, 10-month BW, and 16-month BW, respectively; 0·21, –0·06, and 0·21 for 10-month GFW, 16-month GFW, and 21-month GFW; 0·21, –0·05, and 0·07 for 10-month CFW, 16-month CFW, and 21-month CFW; and –0·09, –0·12, and 0·04 for 10-month FD, 16-month FD, and 21-month FD. When estimates were pooled for all fleece traits and all BW traits, the genetic correlations between FEC0·33 and GFW, CFW, FD, and BW were 0·15, 0·10, –0·06, and –0·21, respectively. Using pooled estimates for CFW, FD, and BW, selection for a breeding objective based on production traits alone would lead to an unfavourable correlated response in FEC0·33 of approximately 1% per year.

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.

Genetic and phenotypic trends and parameters in reproduction, greasy fleece weight and liveweight in Merino lines divergently selected for multiple rearing ability

2004 ◽  
Vol 44 (8) ◽  
pp. 745 ◽  
Author(s):  
S. W. P. Cloete ◽  
A. R. Gilmour ◽  
J. J. Olivier ◽  
J. B. van Wyk
Keyword(s):  
Genetic Correlations ◽  
Annual Production ◽  
Production Traits ◽  
Genetic Progress ◽  
Additive Variance ◽  
Genetic Changes ◽  
Environmental Correlations ◽  
Breeding Values ◽  
Reproduction Traits ◽  
Fleece Weight

Genetic and phenotypic trends and parameters were estimated for reproduction, fleece weight and liveweight in a South African Merino population, divergently selected from 1986, either for (H line) or against (L line) maternal multiple rearing ability. Annual reproduction, ewe greasy fleece weight and pre-joining liveweight data were recorded on 809 Merino ewes, from 1986 to 2002. Phenotypic trends indicated divergence in reproduction traits between the H and L lines. The direct additive variance ratio (h2 ± s.e.) for day of lambing was 0.08 ± 0.02. Estimates of h2 for reproduction traits were: 0.10 ± 0.02 for number of lambs born per ewe; 0.04 ± 0.02 for number of lambs weaned per ewe; and 0.04 ± 0.02 for weight of lamb weaned per ewe, corrected for the gender of the lamb. Corresponding h2 estimates for annual production were 0.57 ± 0.06 for greasy fleece weight and 0.48 ± 0.06 for ewe liveweight at joining. Service sire only exerted a significant (P<0.05) effect on day of lambing, but it accounted for merely 2% of the overall phenotypic variation. Ewe permanent environment variance ratios (c2ewe) for the reproduction traits were: 0.07 ± 0.03 for number of lambs born per ewe; 0.11 ± 0.03 for number of lambs weaned per ewe; and 0.11 ± 0.03 for total weight of lamb weaned per ewe. Corresponding c2ewe estimates for annual production traits were 0.14 ± 0.05 for greasy fleece weight and 0.27 ± 0.06 for ewe joining weight. Genetic and ewe permanent environmental correlations between measures of reproduction exceeded 0.7. Genetic correlations of reproduction traits with greasy fleece weight were low and variable in sign. Genetic correlations of reproduction traits with ewe joining weight were positive and particularly high for weight of lamb weaned. Permanent environmental correlations of reproduction traits with greasy fleece weight and joining weight were generally low to moderate. Genetic trends for the H and L lines (derived from averaged direct breeding values within birth years) were divergent (P<0.01) for all reproduction traits. Expressed as percentage of the overall least squares means of the respective traits, breeding values in the H line increased annually, with 1.3% for lambs born per ewe, 1.5% for lambs weaned per ewe and by 1.8% for weight of lamb weaned per ewe. Corresponding trends in the L line were, respectively, –0.6%, –1.0% and –1.2% per year. Substantial genetic progress in annual lamb output was attainable, despite relatively small h2 estimates. This response was achieved without unfavourable genetic changes in wool and liveweight.

Can we breed Merino sheep with softer, whiter, more photostable wool?

2010 ◽  
Vol 50 (12) ◽  
pp. 1089 ◽  
Author(s):  
S. Hatcher ◽  
P. I. Hynd ◽  
K. J. Thornberry ◽  
S. Gabb
Keyword(s):  
Genetic Parameters ◽  
Selection Index ◽  
Genetic Correlations ◽  
Genetic Selection ◽  
Phenotypic Selection ◽  
Quality Traits ◽  
Current Generation ◽  
Merino Sheep ◽  
Initial Cohort ◽  
Selection For

Genetic parameters (heritability, phenotypic and genetic correlations) were estimated for a range of visual and measured wool traits recorded from the 2008 shearing of the initial cohort of Merino progeny born into the Sheep CRC’s Information Nucleus Flock. The aim of this initial analysis was to determine the feasibility of selectively breeding Merino sheep for softer, whiter, more photostable wool and to quantify the likely impact on other wool production and quality traits. The estimates of heritability were high for handle and clean colour (0.86 and 0.70, respectively) and moderate for photostability (0.18), with some evidence of maternal effects for both handle and photostability. The phenotypic correlations between handle and clean colour and between handle and photostability were close to zero, indicating that achieving the ‘triple’ objective of softer, whiter, more photostable wool in the current generation through phenotypic selection alone would be difficult. There was evidence of an antagonistic relationship between handle and photostability (–0.36), such that genetic selection for softer wool will produce less photostable wool that will yellow on exposure to UV irradiation. However genetic selection for whiter wool is complementary to photostability and will result in whiter wool that is less likely to yellow. Genetic selection to improve handle, colour and photostability can be achieved with few detrimental effects on other visual and measured wool traits, particularly if they are included in an appropriate selection index.

Selection for fertility in Australian Merino sheep

1963 ◽  
Vol 14 (4) ◽  
pp. 460 ◽  
Author(s):  
SSY Young ◽  
HN Turner ◽  
CHS Dolling
Keyword(s):  
Body Weight ◽  
Genetic Correlations ◽  
Fibre Diameter ◽  
Likelihood Method ◽  
Mass Selection ◽  
Genetic Progress ◽  
Subsequent Performance ◽  
Fertility Trait ◽  
Selection For ◽  
The Difference

Phenotypic and genetic parameters for fertility in sheep, in terms of number of lambs born and number weaned, have been estimated in a flock of medium Peppin Merinos. Repeatability of fertility traits over all ages is low, but there is an age effect, the record at 3 years of age having a higher value than those at 2 or 4 years. The regression of subsequent performance on a difference of 1 lamb at the initial lambing was higher for the difference between 1 and 2 lambs than between 0 and 1 lamb, which indicated that selection for twins is likely to raise fertility in the current flock more rapidly than selection against barrenness. The estimate of heritability for 2 years of age was negligible for each fertility trait, but the estimates for the 3-year-old record were higher, the value for lambs born being over 0.3. Mass selection for number of lambs born at 3 years of age would thus be expected to lead to appreciable genetic progress, while there would be at least some progress in number of lambs weaned. Phenotypic and genetic correlations were also estimated between fertility at different ages and 10 sheep and wool traits measured at 15–16 months of age. Phenotypically, fertility is positively correlated with body weight and negatively with skin wrinkle score. Genetically, it is suggested from the estimates that fertility is positively correlated with body weight and staple length and negatively correlated with fibre diameter, clean scoured yield, and wrinkle score. No phenotypic or genetic correlation was found between greasy or clean wool weight and either measure of fertility. The application of the findings to breeding for higher fertility is discussed. In an appendix, a maximum likelihood method of estimating heritability for all-or-none traits in half-sib data is presented.

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

Response to selection in Australian Merino sheep. VIII.* Further results on selection for high clean wool weight with attention to quality

1978 ◽  
Vol 29 (3) ◽  
pp. 615 ◽  
Author(s):  
HN Turner ◽  
N Jackson
Keyword(s):  
Genetic Correlations ◽  
Fibre Diameter ◽  
Control Group ◽  
Environment Interaction ◽  
Genetic Progress ◽  
Weight One ◽  
The Mean ◽  
Selection For ◽  
Made In ◽  
Australian Merino

Results of selection for high clean wool weight per head with control of quality are reported for two selection groups over the period 1966–74. Results for the same experiment for the periods 1950–1959 and 1961–64 were reported earlier. Both groups were selected for high clean wool weight, one (S) with a ceiling on fibre diameter and degree of skin wrinkle, and the other (MS) with a lower limit on staple crimp frequency and a ceiling on skin wrinkle. Genetic progress in clean wool weight was greater in S than in MS over the 1966–74 period (0.12–0.15 lb/annum, compared with 0.06–0.09). This was to be expected from genetic correlations of clean wool weight with fibre diameter (low positive) and staple crimp frequency (high negative). The result supports the previous recommendation that staple crimp frequency is an inefficient way of controlling wool quality while attempting to improve quantity by selection, because its use severely restricts the likely progress in quantity. The actual rate of progress in the S group was similar to that in the period 1950–59, which was followed by a fall in superiority of the selected over the control group animals born during 1961–64. The recovery of response in the 1966–74 period negates the suggestion that the loss of response during the 1961-64 period was due to a 'plateau'. The most likely explanation is that a genotype x environment interaction occurred, such that the genetic gain made in the 1950-59 period could not be expressed in the poorer environments of 1960–65, but reappeared gradually under the improving environment of the 1966–74 period. Attempts to remove this interaction by regression of response on the mean clean wool weight of the unselected control group (as an index of the level of the environment) for each year, were not successful. The interaction is, therefore, not simply a case of all selection groups being equal when the environment is poor. ________________ *Part VII, Aust. J. Agric. Res., 26: 937 (1975).

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