scholarly journals AN APPRAISAL OF SELECTION IN THE ROMNELET SHEEP

1961 ◽  
Vol 41 (2) ◽  
pp. 205-211
Author(s):  
H. F. Peters ◽  
S. B. Slen ◽  
H. J. Hargrave
Keyword(s):  
Birth Weight ◽  
Selection Pressure ◽  
Upward Trend ◽  
Weaning Weight ◽  
Selection For ◽  
Fleece Weight ◽  
One Year ◽  
Selection Differentials ◽  
Made In ◽  
Genetic Trends

The amounts of selection for birth weight, weaning weight, post-weaning gain up to about 1 year of age and yearling clean fleece weight in the development of the Romnelet breed of sheep are reported.The selection differentials for weaning weight only were statistically significant (P < 0.05) for both sexes. Analyses of regression of mean differential on time showed an upward trend in the differentials for birth weight and weaning weight, but there was no evidence of significant yearly trend in the differentials for post-weaning traits. Trends in selection pressure were consistent with the reported genetic trends in performance after the initial decline in performance from F1 to F2.Weaning weight received more attention in selection than any other trait studied, and the most genetic improvement was made in this trait. The large reduction in numbers of animals available for selection from birth to one year of age, due mainly to heavy culling of lambs at weaning, brought about a reduction in selection intensity from 22 per cent to 10 per cent for post-weaning gain and from 42.5 to 22 per cent for clean fleece weight.

The role of selection in the improvement of Welsh Mountain sheep

1958 ◽  
Vol 9 (6) ◽  
pp. 819 ◽  
Author(s):  
JM Doney
Keyword(s):  
Birth Weight ◽  
Maternal Environment ◽  
Weaning Weight ◽  
Phenotypic Correlations ◽  
Selection For ◽  
Heritability Estimates ◽  
Fleece Weight ◽  
Staple Length

Means and variances of several economic characters in Welsh Mountain sheep are given. The repeatabilities of, and phenotypic correlations between, these characters are generally within the range of similar estimates given for other breeds. Heritabilities, calculated from parent-offspring correlations, were : birth weight 0.39, weaning weight 0.68, 18-month weight 0.59, greasy fleece weight 0.61, and staple length 0.73. These values are in general higher than similarly derived estimates from other breeds. A method of correcting heritability estimates to remove the error due to correlation between maternal environment, and the character as measured in the dam, is described. This reduces the estimate for weaning weight to 0.48, and that for 18-month weight to 0.16, but does not change that for fleece weight. The use of such estimates in predicting the effect of selection is discussed, and it is concluded that accurate selection for the chosen economic characters will result in improvement at the present genetic stage of the breed.

scholarly journals GENETIC TRENDS IN PERFORMANCE OF THE ROMNELET SHEEP DURING THE PERIOD OF BREED DEVELOPMENT

1961 ◽  
Vol 41 (1) ◽  
pp. 126-133 ◽  
Author(s):  
H. F. Peters ◽  
S. B. Slen ◽  
H. J. Hargrave
Keyword(s):  
Birth Weight ◽  
Early Years ◽  
Weaning Weight ◽  
Significant Change ◽  
Fleece Weight ◽  
F2 Generation ◽  
Genetic Trends

Performance records on the Romnelet sheep, developed from the Romney X Rambouillet cross [with introductions of Targhee and Romeldale in the early years], were analysed to determine genetic trends in birth weight, weaning weight, 18-month weight of ewes and yearling clean fleece weight from the F1 to the F7 generation.There were statistically significant (P < 0.01) reductions of 1.3 pounds in birth weight, 7.5 pounds in weaning weight at an average age of 136 days, 7.0 pounds in 18-month weight of ewes and 0.6 pound in yearling clean fleece weight from the first-cross to the F2 generation. There was a further significant (P < 0.05) decline of 0.6 pound in birth weight and a significant (P < 0.01) decline of 0.5 pound in clean fleece weight after the F2 generation, but no further significant change occurred in 18-month weight of ewes. There was a significant (P < 0.05) increase of 7.8 pounds in weaning weight in the later generations.

scholarly journals Differential response from selection for high calving ease vs. low birth weight in American Simmental beef cattle

2020 ◽  
Vol 98 (7) ◽  
Author(s):  
Hamad M Saad ◽  
Milton G Thomas ◽  
Scott E Speidel ◽  
Richard K Peel ◽  
W Marshall Frasier ◽  
...  
Keyword(s):  
Birth Weight ◽  
Low Birth Weight ◽  
Selection Index ◽  
Differential Response ◽  
Direct Selection ◽  
Weaning Weight ◽  
Calving Ease ◽  
Selection For ◽  
Maternal Grandsire ◽  
Genetic Trends

Abstract Data on calving ease (CE) and birth, weaning weight (WW), and yearling weight (YW) were obtained from the American Simmental Association (ASA) and included pedigree and performance information on 11,640,735 animals. Our objective was to quantify differential response from selection for high CE vs. low birth weight (LBW) in first-calf Simmental heifers. We hypothesized that direct selection for CE should be used as the primary approach to reduce dystocia and mitigate losses in growth-related traits. WW and YW were adjusted to 205 and 365 d of age, respectively. Sire and maternal grandsire (co)variance components for CE, birth weight (BW), and 205-d weaning weight (205-d WW), and sire covariance components for 160-d postweaning gain (160-d gain) were estimated using a sire-maternal grandsire model. Direct and maternal expected progeny differences (EPD) for CE, BW, and 205-d WW and direct EPD for 160-d gain and 365-d yearling weight (365-d YW) for first-calf Simmental heifers population (465,710 animals) were estimated using a threshold-linear multivariate maternal animal model. This population was used to estimate genetic trends and as a selection pool (control) for various selection scenarios. Selection scenarios were high CE (HCE), LBW, the all-purpose selection index (API = −1.8 BW + 1.3 CE + 0.10 WW + 0.20 YW) of the ASA and its two derived subindices: (API1 = 1.3 CE + 0.20 YW) and (API2 = −1.8 BW + 0.20 YW), and lastly Dickerson’s selection index (DSI = −3.2 BW + YW). Data for each selection scenario were created by selecting sires with EPD greater than or equal to the average along with the top 75% of dams. Comparison between selection scenarios involved evaluating the direct and maternal genetic trends from these scenarios. Direct heritabilities for CE, BW, 205-d WW, 160-d gain, and 365-d YW of Simmental cattle were 0.23, 0.52, 0.28, 0.21, and 0.33, respectively. The single trait, HCE, selection scenario, as opposed to LBW, increased the intercept for CE by 57.7% and the slopes (P &lt; 0.001) for BW, 205-d WW, 160-d gain, and 365-d YW by 27.9%, 37.5%, 16%, and 28%, respectively. Comparisons of various selection scenarios revealed that the CE-based selection scenarios (HCE, API, and API1) had a greater response for CE and growth traits.

Bayesian analysis of selection for greater weaning weight while maintaining birth weight in beef cattle

2009 ◽  
Vol 87 (10) ◽  
pp. 3089-3096 ◽  
Author(s):  
L. M. Melucci ◽  
A. N. Birchmeier ◽  
E. P. Cappa ◽  
R. J. C. Cantet
Keyword(s):  
Birth Weight ◽  
Beef Cattle ◽  
Bayesian Analysis ◽  
Weaning Weight ◽  
Selection For

Estimates of genetic parameters for pre-weaning and post-weaning growth traits of Chios lambs

1980 ◽  
Vol 30 (2) ◽  
pp. 271-276 ◽  
Author(s):  
A. P. Mavrogenis ◽  
A. Louca ◽  
O. W. Robison
Keyword(s):  
Body Weight ◽  
Birth Weight ◽  
Genetic Parameters ◽  
Growth Traits ◽  
Genetic Correlations ◽  
Heritability Estimate ◽  
Weaning Weight ◽  
Phenotypic Correlations ◽  
Selection For ◽  
Daily Gain

ABSTRACTData on 792 Chios lambs born during the 1972/73 and 1973/74 lambing seasons were used to estimate genetic and phenotypic parameters for birth weight, weaning weight, age at weaning, pre-weaning daily gain, body weight at 5, 10, 15 and 20 weeks of age, and postweaning daily gain. Body weight at 15 weeks of age had the highest heritability estimate (0·73 ± 0·17) and that of post-weaning daily gain was also high (0·56 ± 0·15). Selection for either weight at 15 weeks or post-weaning daily gain would be expected to yield a greater response than selection for pre-weaning daily gain or weaning weight. Genetic correlations among weights and/or gains were positive (approximately 0·20). Phenotypic correlations among weights and gains were generally higher than genetic correlations. However, the correlation between pre— and post-weaning daily gain was small (0·08). Likewise, post-weaning daily gain had low correlations with all weights before 10 weeks. Age at weaning had moderate negative associations with all weights but a very low positive correlation with post-weaning daily gain.

Genetic trends for weaning weight during development of a multibreed population of beef cattle in two contrasting environments

2000 ◽  
Vol 80 (1) ◽  
pp. 191-193
Author(s):  
J. J. Tosh ◽  
R. A. Kemp
Keyword(s):  
Natural Selection ◽  
Beef Cattle ◽  
Key Words ◽  
Genetic Component ◽  
Weaning Weight ◽  
Common Base ◽  
The Difference ◽  
Selection Differentials ◽  
Genetic Trends

Genetic trends for weaning weight were determined in two herds of multibreed beef cattle that originated from a common base and were subject to mutual breeding policies in separate environments. The herds diverged for the direct though not the maternal genetic component of weaning weight within the 13-yr period examined; in the final year, the difference (P < 0.001) between the herds was almost 3 kg. This could have been partly due to unequal selection differentials and generation intervals. Results suggested the extent of natural selection also differed between the two environments. Key words: Beef cattle, crossbreeding, genetic trends, selection, weaning weight

MASS SELECTION FOR POST-WEANING GROWTH IN SWINE. V. CORRELATED RESPONSE OF REPRODUCTIVE TRAITS AND PRE-WEANING GROWTH

1976 ◽  
Vol 56 (4) ◽  
pp. 791-801
Author(s):  
I. GARNETT ◽  
G. W. RAHNEFELD
Keyword(s):  
Birth Weight ◽  
Average Daily Gain ◽  
Reproductive Traits ◽  
Correlated Response ◽  
Mass Selection ◽  
Gestation Length ◽  
Control Line ◽  
Weaning Weight ◽  
Selection For ◽  
Daily Gain

Female reproductive performance and pre-weaning survival and growth were examined in a population of swine over 11 generations of selection for post-weaning average daily gain (ADG). Three separate breeding groups were used: (1) a Lacombe (L) line selected each generation for ADG, (2) a Yorkshire control (Y) line, and (3) a crossbred Lacombe × Yorkshire group (LY) generated each generation from the L and Y lines. Breeding group differences were evident for litter size, perinatal mortality, pre-weaning mortality, gestation length, birth weight, pre-weaning average daily gain (PreADG) and weaning weight. Selection did not affect number born, number born alive, number weaned or birth weight. When the values for the L line were expressed as a deviation from the control, pre-weaning mortality showed an increase. The increase appeared to be due to a decrease in the control rather than an increase in the L line. Gestation length showed a negative response to selection. As in the case of pre-weaning mortality, the response appeared to be a reflection of the instability of the control line. Genetic gains in PreADG of 0.004 kg/day/generation were realized in both the L line and LY group. Correspondingly, responses of 0.18 and 0.19 kg/generation were realized for weaning weight in the L line and LY group.

Performance of Hereford and crossbred Hereford cattle in the subtropics of New South Wales: genetic analyses of pre-weaning performance of first-cross calves

1980 ◽  
Vol 31 (2) ◽  
pp. 417 ◽  
Author(s):  
R Barlow ◽  
GH O'Neill
Keyword(s):  
Birth Weight ◽  
Genetic Correlations ◽  
Environmental Variation ◽  
Direct Selection ◽  
Gestation Length ◽  
Strongly Correlated ◽  
Weaning Weight ◽  
Selection For ◽  
Sire Breed ◽  
Size At Birth

First-cross calves of Simmental (S), Friesian (F), and Brahman (B) sires were compared with straight-bred calves of Hereford (H) sires over 5 years at Grafton, N.S.W. There was a total of 775 calves sired by 205 bulls with complete records of performance from conception to weaning. Analyses were conducted to determine sire breed and sire breed x environment effects, and to provide paternal half-sib estimates of heritabilities and genetic and phenotypic correlations. Various models were used to ascertain the sensitivity of genetic parameters to the removal of different sources of variation. Among females, S x H were heaviest at birth, while among males, B x H were heaviest. The regression coefficient of birth weight on gestation length was significantly greater for B x H calves than for other crosses. All crosses grew significantly faster to weaning and were significantly heavier at weaning than H x H calves. However, there were a number of significant interactions between sire breed and environmental variables for measures of pre-weaning growth. S x H and F x H calves appeared most sensitive to environmental variation, while B x H appeared least sensitive. The significance of this is discussed. Estimates of heritability for most traits were high. Values derived by using simple models were: gestation length, 0.68; birth weight, 0.56; average daily gain (ADG) to weaning, 0.47; weaning weight, 0.54; eyelid pigmentation, 0.50. Heritabilities of birth weight and ADG during the early pre-weaning period appeared most sensitive to the amount of environmental variation removed in the model. Gestation length was positively correlated with size at birth but negatively correlated with growth to weaning. There were large positive genetic correlations among various measures of size at birth, and among various measures of growth to weaning. When compared with ADG to weaning, weaning weight was more strongly correlated with birth weight, but less strongly correlated with gestation length. The results also indicated that selection for gain over a fixed time period, immediately prior to weaning, would be as efficient as direct selection for total ADG to weaning.

Productivity of classers' grades and sire selection differentials for fleece weight in two Merino studs

1982 ◽  
Vol 22 (117) ◽  
pp. 274
Author(s):  
BJ McGuirk ◽  
M Rose ◽  
R Scott
Keyword(s):  
Fibre Diameter ◽  
Selection Procedure ◽  
The Other ◽  
Average Fibre Diameter ◽  
Average Coefficient ◽  
Average Fibre ◽  
Selection For ◽  
Fleece Weight ◽  
Selection Differentials ◽  
Sire Selection

The normal practice in Merino studs is to class the rams visually into three grades: reserve rams from which the stud sires will be chosen; flock rams for use in commercial flocks; and culls. This study examined the productivity of these grades in three drops of rams from each of two studs. In each drop there were differences between the grades in greasy and clean fleece weight. In stud 1 the relative clean and greasy wool percentages in the reserve, flock and cull grades were 11 6,98 and 86, and 11 6,98 and 87 (P < 0.05), respectively. Clean fleece weights were not available on the visual culls in stud 2. In that stud the relative greasy wool percentages of rams in three grades were 112, 98 and 90, and the reserve rams also cut 15% more clean wool than the flock rams (P< 0.05). The differences between the grades in yield and average fibre diameter were less than they were for fleece weight and generally not statistically significant. In stud 1 the reserve rams were 0.6% higher yielding and 0.2 pm stronger than the drop average. The reserve rams were less variable than the other grades in fleece weights, yield and diameter. The largest differences were for fleece weights, where the differences in variation between the grades were significant. The average coefficient of variation for greasy fleece weight among the reserve rams in the two studs was 10.0% compared with the estimate of 13.2% for the whole drop. Selection differentials for fleece weight were estimated for stud sires selected from these six drops of rams. The efficiency of sire selection for either greasy or clean fleece weight was in excess of 70% of the maximum possible. In the four drops in which all sire replacements were selected exclusively from the reserves, the two steps in the sire selection procedure contribution almost equally to the sire selection differentials achieved.

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