Increased litter size in Rambouillet sheep: I. Estimation of genetic parameters.

The variance and covariance components needed to estimate heritabilities of and genetic correlations among litter size, ovulation rate, scrotal circumference, and BW in a flock of Rambouillet sheep were estimated using REML via an expectation-maximization type algorithm. The heritability estimates from univariate analyses were .14, .21, .25, .36, and .15 for litter size, ovulation rate, scrotal circumference, 180-d BW of females, and 180-d BW of males, respectively, and average heritability estimates from bivariate analyses were .19, .20, .20, .34, and .10 for litter size, ovulation rate, scrotal circumference, 180-d BW of females, and 180-d BW of males, respectively. The genetic correlation between litter size and ovulation rate was near unity. Body weight in ewes had a moderate genetic correlation with both litter size (.22) and ovulation rate (.20) and a low residual correlation with both litter size (.03) and ovulation rate (.09). The genetic correlation between BW in rams and scrotal circumference was 0, whereas the residual correlation was .71. The genetic correlations of scrotal circumference with litter size and ovulation rate were -.25 and +.20, respectively.     

"Quasi-REML" correlation estimates between production and health traits in the presence of selection and confounding: a simulation study

Performance of the "quasi-REML" method for estimating correlations between a continuous trait and a categorical trait, and between two categorical traits, was studied with Monte Carlo simulations. Three continuous, correlated traits were simulated for identical populations and three scenarios with either no selection, selection for one moderately heritable trait (Trait 1, h2 = .25), and selection for the same trait plus confounding between sires and management groups. The "true" environmental correlations between Traits 2 (h2 = .10) and 3 (h2 = .05) were always of the same absolute size (.20), but further data scenarios were generated by setting the sign of environmental correlation to either positive or negative. Observations for Traits 2 and 3 were then reassigned to binomial categories to simulate health or reproductive traits with incidences of 15 and 5%, respectively. Genetic correlations (r(g12), r(g13), and r(g23) and environmental correlations (r(e12), r(e13), and r(e23)) were estimated for the underlying continuous scale (REML) and the visible categorical scales ("quasi-REML") with linear multiple-trait sire and animal models. Contrary to theory, practically all "quasi-REML" genetic correlations were underestimated to some extent with the sire and animal models. Selection inflated this negative bias for sire model estimates, and the sign of r(e23) noticeably affected r(g23) estimates for the animal model, with greater bias and SD for estimates when the "true" r(e23) was positive. Transformed "quasi-REML" environmental correlations between a continuous and a categorical trait were estimated with good efficiency and little bias, and corresponding correlations between two categorical traits were systematically overestimated. Confounding between sires and contemporary groups negatively affected all correlation estimates on the underlying and the visible scales, especially for sire model "quasi-REML" estimates of genetic correlation. Selection, data structure, and the (co)variance structure influences how well correlations involving categorical traits are estimated with "quasi-REML" methods.     

Genetic parameters for racing records in trotters using linear and generalized linear models

Heritability and repeatability and genetic and phenotypic correlations were estimated for trotting race records with linear and generalized linear models using 510,519 records on 17,792 Finnhorses and 513,161 records on 25,536 Standardbred trotters. Heritability and repeatability were estimated for single racing time and earnings traits with linear models, and logarithmic scale was used for racing time and fourth-root scale for earnings to correct for nonnormality. Generalized linear models with a gamma distribution were applied for single racing time and with a multinomial distribution for single earnings traits. In addition, genetic parameters for annual earnings were estimated with linear models on the observed and fourth-root scales. Racing success traits of single placings, winnings, breaking stride, and disqualifications were analyzed using generalized linear models with a binomial distribution. Estimates of heritability were greatest for racing time, which ranged from 0.32 to 0.34. Estimates of heritability were low for single earnings with all distributions, ranging from 0.01 to 0.09. Annual earnings were closer to normal distribution than single earnings. Heritability estimates were moderate for annual earnings on the fourth-root scale, 0.19 for Finnhorses and 0.27 for Standardbred trotters. Heritability estimates for binomial racing success variables ranged from 0.04 to 0.12, being greatest for winnings and least for breaking stride. Genetic correlations among racing traits were high, whereas phenotypic correlations were mainly low to moderate, except correlations between racing time and earnings were high. On the basis of a moderate heritability and moderate to high repeatability for racing time and annual earnings, selection of horses for these traits is effective when based on a few repeated records. Because of high genetic correlations, direct selection for racing time and annual earnings would also result in good genetic response in racing success.     

Genetic correlations between osseous fragments in fetlock and hock joints, deforming arthropathy in hock joints and pathologic changes in the navicular bones of Warmblood riding horses

The results of a standardized radiological examination of 5231 Hanoverian Warmblood horses were used to investigate heritability of and genetic correlations between prevalent radiographic findings in the equine limbs. Radiographic findings were categorized by joint location and type of visible alterations and analyzed as all-or-none traits. Heritabilities and correlations were estimated multivariately for most prevalent radiographic findings in equine limbs using Residual Maximum Likelihood (REML) and Gibbs Sampling (GS). Linear animal models and linear sire models were used for REML; sire threshold models were used for GS analyses. Heritabilities and residual correlations from linear model analyses were transformed from observed scale to underlying liability scale. Osseous fragments were seen in fetlock joints (OFF) of 23.5% and in hock joints (OFH) of 9.2% of investigated horses. Deforming arthropathy in hock joints (DAH) was diagnosed in 12.0% and pathologic changes in navicular bones (PCN) in 25.8% of investigated horses. Heritabilities differed little between analyses with animal and sire models and with REML and GS. Ranges of heritability estimates were h² = 0.16–0.44 with REML and h² = 0.07–0.43 with GS. Genetic correlation estimates were larger in GS than in REML analyses. Additive genetic correlation between OFF and DAH was positive (r_g = 0.25 to 0.77). Negative additive genetic correlations were determined between OFF and OFH (r_g = − 0.17 to − 0.82), between OFH and DAH (r_g = − 0.14 to − 0.81), and between OFH and PCN (r_g = − 0.19 to − 0.26). No relevant additive genetic correlations were estimated between PCN and OFF, and between PCN and DAH. The results of the present study indicate that the prevalences of common radiographic findings in the limbs of young riding horses are relevantly influenced by genetics and probably caused by different genes. Genetic correlations between radiological health traits therefore deserve closer attention in horse breeding. The quantitatively most important radiographic findings should be concurrently considered as individual traits in order to provide for general improvement of radiological health of the limbs of young Warmblood riding horses.     

Heritabilities and genetic correlations of growth and reproductive measurements in Hereford bulls

Weight, hip height, heart girth, pelvic height, pelvic width and scrotal circumference were measured at 403 and 490 d on 427 Hereford bulls. The bulls were members of a random-selection herd so estimates of genetic parameters should have a minimum of bias due to selection. Heritabilities and genetic correlations were estimated by normal paternal half-sib (PHS) correlation procedures. In addition, 256 son-sire pairs (RSS) were used to estimate heritabilities and genetic correlations by regression and covariance methods. The PHS method produced heritability estimates in the range of .41 to .58 for all measures at both ages, with the exceptions of hip height at 403 d (.24) and pelvic height at 490 d (.23). The estimates derived in the RSS method ranged from .10 to .60. The RSS relationship would contain a portion of any maternal X direct covariance effects. A difference in heritability estimated by the two methods could be a reflection of this covariance. Genetic correlations tended to be larger than phenotypic and, in several cases, were negative. The difference in the correlation between two measurements taken at 403 d vs the same correlation estimated at 490 d was not readily explainable but may be evidence for differences in maturation rates or maternal effects. Scrotal circumference had a positive genetic correlation with weight and heart girth and near 0 or negative genetic correlations with pelvic measures. Hip height had positive genetic correlations with weight and heart girth at 403 and 490 d and with pelvic measurements at 403 d, but the correlations were not as large at 490 d.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differences in heritability estimates from multiple-trait and repeated-records models.

Analyses of ovulation rates in consecutive estrous cycles with multiple-trait and repeated-records animal models resulted in different estimates of heritability. The estimate from the repeated-records model was seen to be approximately the product of the average genetic correlation and the average heritability from the multiple-trait procedure. A simple model is used to show algebraically that such a result is expected, particularly if the environmental correlations are small among records of the same animal. Comparison of results of the two types of analyses of 10 replications of 10 combinations of underlying heritabilities and genetic correlations confirms this explanation.     

Estimation of genetic parameters for wool fiber diameter measures.

Genetic and phenotypic correlations and heritability estimates of side, britch, and core diameters; side and britch CV; side and britch diameter difference; and clean fleece weight were investigated using 385 western white-faced ewes produced by 50 sires and maintained at two locations on a selection study. Data were analyzed using analysis of variance procedures, and effects in the final model included breed of sire-selection line combination, sire within breed-selection line, and location. Heritabilities were estimated by paternal half-sib analysis. Sires within breed-selection line represented a significant source of variation for all traits studied. Location had a significant effect on side diameter, side and britch diameter difference, and clean fleece weight. Age of ewe only affected clean fleece weight. Phenotypic and genetic correlations among side, britch, and core diameter measures were high and positive. Phenotypic correlations ranged from .68 to .75 and genetic correlations ranged from .74 to .89. The genetic correlations between side and britch diameter difference and side diameter or core diameter were small (-.16 and .28, respectively). However, there was a stronger genetic correlation between side and britch diameter difference and britch diameter (.55). Heritability of the difference between side and britch diameter was high (.46 +/- .16) and similar to heritability estimates reported for other wool traits. Results of this study indicate that relatively rapid genetic progress through selection for fiber diameter should be possible. In addition, increased uniformity in fiber diameter should be possible through selection for either side and britch diameter difference or side or britch CV.     

Genotypic expression at different ages: I. Prolificacy traits of sheep.

Genetic parameters for prolificacy traits for Columbia (COLU), Polypay (POLY), Rambouillet (RAMB), and Targhee (TARG) breeds of sheep were estimated with REML using animal models. Traits were number of live births (LAB), litter size at birth (LSB) and weaning (LSW), and litter weight weaned (LWW). Numbers of observations ranged from 5,140 to 7,095 for prolificacy traits and from 5,101 to 8,973 for litter weight weaned for the four breeds. For single-trait analyses, ewes were classified as young (1 yr old), middle-aged (2 and 3 yr old), or older (> 3 yr old). After single-trait analyses, three-trait analyses were done for each characteristic with traits defined by age class. Generally, heritability estimates from single-trait analyses were low and ranged from .01 to .17 for LAB and LSB and from .00 to .10 for LSW. Heritability estimates obtained for LWW ranged from low to moderate (.00 to .25) and were less for older ewes. Heritability estimates from the three-trait analyses were generally similar to estimates from single-trait analyses. Heritabilities for LAB and LSB were similar, and, for three-trait analyses, they ranged across age groups from .07 to .13 for COLU, .13 to .16 for POLY, .10 to .16 for RAMB, and .01 to .16 for TARG. Estimates for LSW from three-trait analyses ranged from .07 to .12 for COLU, .04 to .09 for POLY, .01 to .11 for RAMB, and .03 to .11 for TARG. For LWW, heritabilities ranged from .00 to .21 for COLU, .05 to .08 for POLY, .12 to .15 for RAMB, and .18 to .29 for TARG. Genetic correlations for LAB, LSB and LSW among age-defined traits ranged from .25 to 1.00. Genetic correlations for LAB and LSB between young and middle and between young and older age classes were less than .80 in COLU, POLY, and RAMB breeds. Only genetic correlations between middle and older age classes for these breeds were greater than .80. For TARG, genetic correlations among all age classes were greater than .80 (.88 to 1.00) for those traits. All genetic correlations among ages for LSW were greater than .80 for POLY and TARG. For RAMB, only the correlation between young and older age classes for LSW was less than .80 (.45). None was greater than .80 for COLU. For LWW, genetic correlations among all age classes in POLY and RAMB were greater than .80 (.82 to 1.00). For COLU, genetic correlation between young and middle was low (.07), between young and older was high (.88), and between middle and older classes was moderately high (.54). For TARG, genetic correlations were .49, .65, and .98 for young-middle, young-older, and middle-older age classes, respectively. Results indicate that more progress could be made in selection programs for prolificacy traits in some sheep breeds by considering age of ewe as a part of the trait rather than by simply adjusting for ages of ewes.     

Genetic parameter estimates for growth traits in Horro sheep

Variance components and genetic parameters were estimated for growth traits: birth weight (BWT), weaning weight (WWT), 6‐month weight (6MWT) and yearling weight (YWT) in indigenous Ethiopian Horro sheep using the average information REML (AIREML). Four different models: sire model (model 1), direct animal model (model 2), direct and maternal animal model (model 3) and direct–maternal animal model including the covariance between direct and maternal effects (model 4) were used. Bivariate analysis by model 2 was also used to estimate genetic correlation between traits. Estimates of direct heritability obtained from models 1–4, respectively, were for BWT 0.25, 0.27, 0.18 and 0.32; for WWT, 0.16, 0.26, 0.1 and 0.14; for 6MWT 0.18, 0.26, 0.16 and 0.16; and for YWT 0.30, 0.28, 0.23, and 0.31. Maternal heritability estimates of 0.12 and 0.23 for BWT; 0.19 and 0.24 for WWT; 0.09 and 0.09 for 6MWT and 0.08 and 0.14 for YWT were obtained from models 3 and 4, respectively. The correlations between direct and maternal additive genetic effects for BWT, WWT, 6MWT and YWT were –0.64, –0.42, 0.002 and –0.46, respectively. On the other hand, the genetic correlations between BWT and the rest of growth traits (WWT, 6MWT and YWT, respectively) were 0.45, 0.33 and 0.31, whereas correlations between WWT and 6MWT, WWT and YWT and 6MWT and YWT were 0.98, 0.84 and 0.87, respectively. The medium to high direct and maternal heritability estimates obtained for BWT and YWT indicate that in Horro sheep faster genetic improvement through selection is possible for these traits and it should consider both (direct and maternal) h² estimates. However, since the direct‐maternal genetic covariances were found to be negative, caution should be made in making selection decisions. The high genetic correlation among early growth traits imply that genetic improvement in any one of the traits could be made through indirect selection for correlated traits.     

Genetic parameters for intramuscular fat percentage, marbling score, scrotal circumference, and heifer pregnancy in Red Angus cattle

Selection criteria for yearling bulls commonly include indicators of fertility and carcass merit, such as scrotal circumference (SC) and intramuscular fat percentage (IMF). Genetic correlation estimates between ultrasound traits such as IMF and carcass marbling score (MS) with fertility traits SC and heifer pregnancy (HP) have not been reported. Therefore, the objective of this study was to estimate the genetic parameters among the indicator traits IMF and SC, and the economically relevant traits MS and HP. Records for IMF (n=73,051), MS (n=15,260), SC (n=43,487), and HP (n=37,802) were obtained from the Red Angus Association of America, and a 4-generation ancestral pedigree (n=10,460) was constructed from the 8,915 sires represented in the data. (Co)variance components were estimated using a multivariate sire model and average information REML to obtain estimates of heritability and genetic correlations. Fixed effects included contemporary group and the linear effect of age at measurement for all traits, and an additional effect of age of dam for both HP and SC. The random effect of sire was included to estimate additive genetic effects, which were assumed to be continuous for IMF, MS, and SC, but a probit threshold link function was fitted for HP. Generally moderate heritability estimates of 0.29 ± 0.01, 0.35 ± 0.06, 0.32 ± 0.02, and 0.17 ± 0.01 were obtained for IMF, MS, SC, and HP on the underlying scale, respectively. The confidence interval for the estimated genetic correlation between MS and HP (0.10 ± 0.15) included zero, suggesting a negligible genetic association. The genetic correlation between MS and IMF was high (0.80 ± 0.05), but the estimate for HP and SC (0.05 ± 0.09) was near zero, as were the estimated genetic correlations of SC with MS (0.01 ± 0.08) and IMF (0.05 ± 0.06), and for HP with IMF (0.13 ± 0.09). These results suggest that concomitant selection for increased fertility and carcass merit would not be antagonistic.     

Genetic factors contributing to variation in littersize in British Large White gilts

The number of ova released (ovulation rate) by 516 Large White gilts born between 1986 and 1989 was recorded. The weight of the gilt at birth, weaning and time of ovulation rate measurement and her number of teats were also recorded. Parrowing data (number born alive and litter weight at birth) corresponding to the ovulation rate were recorded from 382 of the gilts, enabling calculation of prenatal survival (number born alive/ovulation rate). The data were analysed using univariate and multivariate restricted maximum likelihood (REML) techniques with an individual animal model. The additive genetic direct and maternal components of variance and the common family and residual environmental components of variance and the additive genetic and residual environmental covariances between traits were estimated. The univariate REML analyses showed that the additive genetic direct component was a significant source of variation for gilt weight at birth and weaning, teat number, ovulation rate on the left hand side, total ovulation rate and litter weight at birth. Common family environmental effects were significant sources of variation for gilt weights and teat number. The multivariate REML analyses indicated that the genetic correlations between total ovulation rate and ovulation rate from the left and right ovaries were close to unity, with an estimate of the heritability of total ovulation rate of 0.37±0.09. In the data from gilts that farrowed, the heritabilities of ovulation rate, number born alive and prenatal survival were 0.30±0.10, 0.09±0.06 and 0.00±0.00, respectively. The genetic correlation between ovulation rate and litter size was close to unity, suggesting that genetic variation in ovulation rate explains virtually all of the genetic variation in number born alive in the population of Large White gilts understudy.     

Estimation of genetic parameters and prediction of breeding values for multivariate threshold and continuous data in a simulated horse population using Gibbs sampling and residual maximum likelihood

Simulated horse data were used to compare multivariate estimation of genetic parameters and prediction of breeding values (BV) for categorical, continuous and molecular genetic data using linear animal models via residual maximum likelihood (REML) and best linear unbiased prediction (BLUP) and mixed linear-threshold animal models via Gibbs sampling (GS). Simulation included additive genetic values, residuals and fixed effects for one continuous trait, liabilities of four binary traits, and quantitative trait locus (QTL) effects and genetic markers with different recombination rates and polymorphism information content for one of the liabilities. Analysed data sets differed in the number of animals with trait records and availability of genetic marker information. Consideration of genetic marker information in the model resulted in marked overestimation of the heritability of the QTL trait. If information on 10,000 or 5,000 animals was used, bias of heritabilities and additive genetic correlations was mostly smaller, correlation between true and predicted BV was always higher and identification of genetically superior and inferior animals was - with regard to the moderately heritable traits, in many cases - more reliable with GS than with REML/BLUP. If information on only 1,000 animals was used, neither GS nor REML/BLUP produced genetic parameter estimates with relative bias 50% for all traits. Selection decisions for binary traits should rather be based on GS than on REML/BLUP breeding values.     

Genetic evaluation of meat quality traits and their correlation with growth and carcase composition in Japanese quail

1. Estimates of heritability, genetic and phenotypic correlations of performance and meat quality traits were obtained in a population of Japanese quail using restricted maximum likelihood (REML) procedures.

2. The heritability estimates for body weight (BW) traits ranged from 0·15 at hatch to 0·42 at six weeks. For carcase composition traits, heritability estimates ranged from 0·12 for carcase yield to 0·26 for abdominal fat yield and for meat quality traits they ranged from 0·18 for drip loss to 0·54 for yellowness of the meat.

3. Negative genetic correlations were found between BW and carcase traits with ultimate pH and drip loss ranging from ?0·01 (BW at hatch) to ?0·40 (skin yield). Redness and yellowness showed negative genetic correlations with BW and carcase traits, whereas the genetic correlations with lightness were positive (from 0·04 to 0·43).

4. Shear force and cooking loss showed positive genetic correlations with carcase, breast, abdominal and skin yield.

5. In conclusion, meat quality traits have the potential to be improved through genetic selection but selection for higher BW and carcase composition may reduce the meat quality of Japanese quail through reducing redness, ultimate pH and intramuscular fat and increasing lightness, shear force and cooking loss of the meat.     

Genetic and phenotypic variation in sources of preweaning lamb mortality

Information on causes of mortality to 8 wk weaning for 16,881 lambs of 10 line-breed groups by 594 sires born over a 5-yr period was analyzed by least squares procedures to estimate sire variance and covariance components within line and year-season. Heritability estimates were approximately 5% for total mortality in the binomial scale and near 10% when converted to a normal scale. Average heritability estimates in the binomial and normal scale were, respectively, 4 and 12% for perinatal and 3 and 7% for postnatal mortality. The heritability estimates for respiratory problems were inconsistent; binomial-scale estimates ranged from 0 to 7% in different populations. Regression adjustment for effects of variation in litter size and birth weight caused only minor changes in the heritability estimates. Comparison of covariances among half-sibs vs full-sibs indicated very large maternal effects on perinatal mortality but smaller and less consistent effects on sources of postnatal mortality. Phenotypic correlations among sources of mortality indicated a 26% greater influence of postnatal than perinatal mortality on variation in total mortality, but both the genetic and phenotypic correlations between those two components were slightly negative. These results suggest that the use of family and progeny test selection for transmitted effects on both perinatal and postnatal lamb viability should be effective.     

Genetic, phenotypic, and environmental parameter estimates of calving difficulty, weight, and measures of pelvic size in beef heifers.

The heritabilities for and the genetic, phenotypic, and environmental correlations among calving difficulty scores (CDS) and measures of size of the pelvic inlet were estimated using 547 records of 2-yr-old heifers from three synthetic breed groups. Calving difficulty score was treated first as a trait of the dam and then as a trait of the calf and was analyzed on three scales: raw scores from 0 to 3 (0 = normal birth, 3 = most difficult delivery requiring a hard pull, veterinary assistance, or surgical intervention), Snell-transformed scores, and a binary (0, 1) scale. Estimates of heritability for CDS as a trait of the dam were similar to those when it was considered a trait of the calf. Heritability estimates for CDS on the raw and transformed scales were similar and moderate in magnitude (.36 +/- .15 to .47 +/- .18) but were higher than most reported estimates. However, on the binary scale the estimates were lower (.26 +/- .17, .28 +/- .14). Estimates of heritability for the horizontal and vertical pelvic diameters and the pelvic area were high, implying that pelvic size in heifers might be readily modified by selection. The genetic and phenotypic correlations between CDS as a dam trait and pelvic dimensions were low, whereas the correlations between CDS and dam weight at calving were moderate. As a calf trait, CDS was highly correlated genetically with calf birth weight, but the phenotypic correlations were moderate.     

Estimates of covariances between reproduction and growth in Australian beef cattle

Estimates of covariance components between scrotal circumference, serving capacity, days to calving, and yearling and final weight were obtained for Hereford, Angus, and Zebu cross cattle in temperate and tropical Australia. Analyses were carried out by REML employing a derivative-free algorithm and fitting bivariate animal models. Aspects of modeling and computational requirements related to the use of this method are discussed. Estimates of heritabilities agreed closely with those from univariate analyses, being low for female reproductive performance and moderate to high for male reproduction and growth. Estimates of genetic correlation between male and female fertility traits were low but favorable, being -.25, -.28, and -.41 between scrotal circumference and days to calving for Herefords, Angus, and Zebu crosses, respectively. Genetic correlations between male reproductive traits and weights ranged from .24 to .52 for the temperate breeds and were higher (.65 to .69) for Zebu crosses. Phenotypic correlations between scrotal circumference and weights were similar for all breeds, ranging from .32 to .47, whereas serving capacity and weights were phenotypically unrelated. Estimates of correlations between days to calving and weights were less consistent. Phenotypically, there was little association between the two traits. Genetic correlations for Zebu crosses were negative and low to moderate (-.36 to -.66) and estimates for Angus were close to zero.     

Genetic parameters for fur quality graded on live animals and dried pelts of American mink (Neovison vison)

Fur quality and skin size are integral qualities in the mink industry and are main determinants of sales price and subsequent income for mink fur producers. Parental animals of future generations are selected based on quality grading from live animals, but selection response is obtained from dried skins sold after pelting. In this study, we evaluated traits assessed during live grading and pelt traits examined on dried skins to determine correlation between live and pelt traits. Grading traits and body weight were measured during live animal grading for 9,539 Brown American mink, and pelt quality traits and skin size were evaluated on 8,385 dried mink skins after pelting. Data were sampled from 2 yearly production cycles. Genetic parameters were estimated using the REML method implemented in the DMU package. Heritabilities and proportions of litter variance were calculated from estimated variance components for all traits, and genetic and phenotypic correlations between all traits were estimated in a series of bivariate analyses. Heritability estimates for live grading traits ranged from 0.06 to 0.28, heritability estimates for pelt quality traits ranged from 0.20 to 0.30, and finally heritability estimates for body size traits ranged from 0.43 to 0.48. Skin size and body weight were regarded as different traits for the two sexes and were therefore analysed for each sex separately. Genetic correlations between grading traits exhibited a range of 0.30–0.99 and genetic correlations between pelt quality traits ranged from 0.38 to 0.86. Genetic correlations between quality, wool density and silky appearance evaluated during live animal grading and on dried skin after pelting were 0.74, 0.41 and 0.33, respectively. Skin size and body weight were negatively correlated with pelt quality traits and ranged from −0.55 to −0.25. Using standard selection index theory and combined information from both live grading and skin evaluation increase of reliability of selection ranged from 0.6% to 14%. Due to moderate genetic correlations between traits evaluated during live grading and on dried skins, and negative correlations between pelt quality traits and body size, we concluded that traits should be selected simultaneously.     

A review of genetic parameter estimates for wool, growth, meat and reproduction traits in sheep

Genetic parameters for a range of sheep production traits have been reviewed from estimates published over the last decade. Weighted means and standard errors of estimates of direct and maternal heritability, common environmental effects and the correlation between direct and maternal effects are presented for various growth, carcass and meat, wool, reproduction, disease resistance and feed intake traits. Weighted means and confidence intervals for the genetic and phenotypic correlations between these traits are also presented. A random effects model that incorporated between and within study variance components was used to obtain the weighted means and variances. The weighted mean heritability estimates for the major wool traits (clean fleece weight, fibre diameter and staple length) and all the growth traits were based on more than 20 independent estimates, with the other wool traits based on more than 10 independent estimates. The mean heritability estimates for the carcass and meat traits were based on very few estimates except for fat (27) and muscle depth (11) in live animals. There were more than 10 independent estimates of heritability for most reproduction traits and for worm resistance, but few estimates for other sheep disease traits or feed intake. The mean genetic and phenotypic correlations were based on considerably smaller numbers of independent estimates. There were a reasonable number of estimates of genetic correlations among most of the wool and growth traits, although there were few estimates for the wool quality traits and among the reproduction traits. Estimates of genetic correlations between the groups of different production traits were very sparse. The mean genetic correlations generally had wide confidence intervals reflecting the large variation between estimates and relatively small data sets (number of sires) used. More accurate estimates of genetic parameters and in particular correlations between economically important traits are required for accurate genetic evaluation and development of breeding objectives.     

Genetic parameters of ascites-related traits in broilers: effect of cold and normal temperature conditions

(1) Ascites syndrome is a growth-related disorder of broilers that occurs more often in fast-growing birds and at low temperatures. The objective of this study was to estimate genetic and phenotypic correlations among ascites-related traits measured either under cold or under normal temperature conditions, and to estimate genetic correlations between ascites-related traits measured under cold and normal conditions. (2) Several traits related to ascites were measured on more than 4000 chickens under cold conditions and on more than 700 chickens under normal conditions. (3) The heritability estimates for body weight (BW) measured under cold and normal conditions were 0.42 and 0.50, respectively, for haematocrit value 0.46 and 0.17, respectively, and for ratio of right to total ventricular weight 0.45 and 0.12, respectively. (4) The genetic correlation between BW and haematocrit value under cold conditions was -0.23 and between BW and ratio of right to total ventricular weight -0.27. Under normal conditions, however, these genetic correlations were 0.55 and 0.50, respectively. (5) These results demonstrate that the heritability estimates of ascites-related traits as well as genetic correlations between ascites-related traits and BW depend on the temperature conditions under which animals are kept. (6) Strong positive genetic correlations (around 0.8) were observed between total mortality, fluid in the abdomen and ratio of right to total ventricular weight under cold conditions. The genetic correlation between ratio of right to total ventricular weight under cold and normal conditions was 0.91. (7) These results suggest that the ratio of right to total ventricular weight measured under normal temperature conditions might serve as a good indicator trait for ascites.     

Genetic parameters for nuclear and nonnuclear inheritance in three synthetic lines of beef cattle differing in mature size.

Genetic parameters for nuclear and cytoplasmic genetic effects were estimated from preweaning growth data collected on three synthetic lines of beef cattle differing in mature size. Lines of small-, medium-, and large-framed calves were represented in each of two research herds (Rhodes and McNay). Variance components were estimated separately by herd and size line for birth weight and 205-d weight (WW) by REML with an animal mode using an average of 847 and 427 calf records from Rhodes and McNay, respectively. Model 1 included effects of fixed year, sex of calf, age of dam, and random additive direct (a), additive maternal genetic (m), covariance (a,m), permanent environment affecting the dam, and residual error. Model 2 differed from Model 1 by including random cytoplasmic lineage effects and by ignoring permanent environmental effects. Model 1--direct (maternal) heritability estimates for birth weight at Rhodes were .62(.03) for small, .67(.06) for medium, and .30(.11) for large lines. Genetic correlations between direct and maternal effects for birth weight were .67, -.16, and .48 for the respective size groups. For WW at Rhodes, direct (maternal) heritability estimates were .30(.29), .30(.14), and .10(.16) for small, medium, and large lines, respectively, with genetic correlations of -.34 (small), -.12 (medium), and .17 (large). Heritability estimates at McNay were similar to those at Rhodes, except that maternal genetic heritabilities for WW were smaller (.10, small; .01, medium; .00, large). Model 2--estimates for nuclear genetic effects were consistent with the estimates from Model 1. Cytoplasmic variance accounted for 0 to 5% of the total random variance in birth weight. For WW, cytoplasmic variance was negligible at Rhodes and accounted for 4% of the total random variance in the large line at McNay, averaging less than the permanent environment. Results failed to indicate that cytoplasmic variance was important for preweaning performance.