Estimation of Genetic Parameters and Variance Components for Growth Traits of Nguni Cattle in Limpopo Province,South Africa

Estimates of (co)variance and genetic parameters of birth, weaning (205 days) and yearling (365 days) weight were obtained using single-trait animal models. The data were analysed by restricted maximum likelihood, fitting an animal model that included direct and maternal genetic and permanent environmental effects. The data included records collected between 1976 and 2001. The pedigree information extended as far back as early 1960s. The heritabilities for direct effects of birth, weaning and yearling weights were 0.36, 0.29 and 0.25, respectively. Heritability estimates for maternal effects were 0.13, 0.16 and 0.15 for birth, weaning and yearling weights, respectively. The correlations between direct and maternal additive genetic effects were negative for all traits analysed. The results indicate that both direct and maternal effects should be included in a selection programme for all the traits analysed.     

Estimates of parameters between direct and maternal genetic effects for weaning weight and direct genetic effects for carcass traits in crossbred cattle

Estimates of heritabilities and genetic correlations were obtained for weaning weight records of 23,681 crossbred steers and heifers and carcass records from 4,094 crossbred steers using animal models. Carcass traits included hot carcass weight; retail product percentage; fat percentage; bone percentage; ribeye area; adjusted fat thickness; marbling score, Warner-Bratzler shear force and kidney, pelvic and heart fat percentage. Weaning weight was modeled with fixed effects of age of dam, sex, breed combination, and birth year, with calendar birth day as a covariate and random direct and maternal genetic and maternal permanent environmental effects. The models for carcass traits included fixed effects of age of dam, line, and birth year, with covariates for weaning and slaughter ages and random direct and maternal effects. Direct and maternal heritabilities for weaning weight were 0.4 +/- 0.02 and 0.19 +/- 0.02, respectively. The estimate of direct-maternal genetic correlation for weaning weight was negative (-0.18 +/- 0.08). Heritabilities for carcass traits of steers were moderate to high (0.34 to 0.60). Estimates of genetic correlations between direct genetic effects for weaning weight and carcass traits were small except with hot carcass weight (0.70), ribeye area (0.29), and adjusted fat thickness (0.26). The largest estimates of genetic correlations between maternal genetic effects for weaning weight and direct genetic effects for carcass traits were found for hot carcass weight (0.61), retail product percentage (-0.33), fat percentage (0.33), ribeye area (0.29), marbling score (0.28) and adjusted fat thickness (0.25), indicating that maternal effects for weaning weight may be correlated with genotype for propensity to fatten in steers.     

Genotype by region and season interactions on weaning weight in United States Angus cattle

The objective of this study was to determine if weaning weight performance is genetically consistent across different environments in the United States. The American Angus Association provided weight and pedigree data. Weaning weights observed in the Southeast (SoE) and Northwest (NW) were the focus of this study, as these regions are perceived as opposite extremes in climate. The 2 most represented calving seasons in each region were fall and winter in the SoE and winter and spring in the NW. The original data were edited to remove weaning weight records outside of 3 SD from the respective region-season mean, contemporary groups smaller than 20, and single-sire contemporary groups. The final dataset included 884,465 weaning weight records with 64,907 from fall-born calves in the SoE, 74,820 from winter-born calves in the SoE, 346,724 from winter-born calves in the NW and 398,014 from spring-born calves in the NW. Weaning weights of calves born in different region-season classes adjusted to 205 d of age were considered different but genetically correlated traits in a multivariate analysis. The sole fixed effect was weaning contemporary group and random effects included direct, maternal, maternal permanent environment, and a residual. Direct heritability estimates differed little across environments: 0.31 and 0.35 for weight in fall- and winter-born calves in the SoE, and 0.29 and 0.32 for winter- and spring-born calves in NW. Maternal heritability estimates ranged from 0.12 in the NW to 0.16 the SoE. Genetic correlations spanned from 0.69 to 0.93 among direct effects and from 0.65 to 0.95 among maternal effects. All heritability estimates had small (0.01 to 0.04) SE. The most distinct environments appeared to be winter in SoE and spring in NW (correlations of 0.69 and 0.65 for the direct and maternal effects). Different choices of sires for different environments might be justified to achieve the growth performance expected.     

Genetic analysis of litter size in Targhee, Suffolk, and Polypay sheep

Data on litter size, weaning weights at 60, 90, and 120 d, postweaning gains from weaning to 120 or 365 d of age, fleece weight, and fiber diameter from Targhee, Suffolk, and Polypay flocks participating in the U.S. National Sheep Improvement Program were used to estimate genetic parameters for litter size and genetic relationships between early-life traits and future litter size. Records on 7,591 lambings by 3,131 Targhee ewes, 10,295 lambings by 5,038 Suffolk ewes, and 6,061 lambings by 2,709 Polypay ewes were used. Heritability estimates for litter size ranged from .09 to .11 across breeds; repeatability ranged from .09 to .13. Additive genetic effects on litter size were generally positively, and occasionally significantly, correlated with animal additive genetic effects on weaning weights and postweaning gains. Genetic correlations (r(a)) ranged from .08 to .48 in Targhee and from .17 to .43 in Suffolk but were close to 0 in Polypay (-.14 to .09). Additive maternal effects on weaning weight were positively associated with litter size in Suffolk and Polypay; this correlation was negative (-.23 to -.35), but not significant, in Targhee. Fleece weight was not strongly associated with litter size; (r(a) = -.09 to .21). However, fiber diameter had a significant undesirable correlation with litter size (.30) in Targhee. Estimates of phenotypic correlations of litter size with early-life traits were uniformly small (-.02 to .08). Thus, although occasional genetic antagonisms between litter size and early-life traits were observed in these data, none appeared large enough to prevent simultaneous genetic improvement in both traits.     

Relationships between growth and productivity of range ewes

The relationships between various measures of growth and productivity of range sheep were investigated, utilizing records of 1,109 range ewes sired by 269 rams. Body weights and degree of maturity of body weight at birth, weaning, 12 mo, 18 mo, 30 mo and absolute growth rate, absolute maturing rate and relative growth rate over various age intervals were studied relative to their relationship with productivity characters. Measures of ewe productivity were average annual production for the 4-yr period, 2 through 5 yr of age, for grease fleece weight, number of lambs born, number of lambs weaned and weight of lambs weaned. Heritability estimates were .31 +/- .11 for grease fleece weight, .42 +/- .12 for number of lambs born, .08 +/- .10 for number of lambs weaned and .03 +/- .10 for weight of lambs weaned. All production characters had positive phenotypic correlations (.04 to .22) with body weight at all ages. Both number of lambs born and weight of lambs weaned had small positive phenotypic correlations with growth rates over the 12- to 18-mo age interval. The genetic correlations between ewe productivity and weights at different ages were variable, ranging from -.71 between weaning weight and grease fleece weight to values greater than 1.00 for correlations between weight of lambs weaned and weights at birth, weaning and 18-mo. Degree of maturity at 12 mo had positive genetic correlations with all production characters. Estimated genetic correlations between number of lambs born and absolute growth rate, relative growth rate and absolute maturing rate over the 12- to 18-mo age interval were positive.     

Synthesis of direct and maternal genetic components of economically important traits from beef breed-cross evaluations

Published information on relative performance of beef breed crosses was used to derive combined estimates of purebred breed values for predominant temperate beef breeds. The sources of information were largely from the United States, Canada, and New Zealand, although some European estimates were also included. Emphasis was on maternal traits of potential economic importance to the suckler beef production system, but some postweaning traits were also considered. The estimates were taken from comparison studies undertaken in the 1970s, 1980s and 1990s, each with representative samples of beef breeds used in temperate agriculture. Weighting factors for breed-cross estimates were derived using the number of sires and offspring that contributed to that estimate. These weights were then used in a weighted multiple regression analysis to obtain single purebred breed effects. Both direct additive and maternal additive genetic effects were estimated for preweaning traits. Important genetic differences between the breeds were shown for many of the traits. Significant regression coefficients were estimated for the effect of mature weight on calving ease, both maternal and direct additive genetic, survival to weaning direct, and birth weight direct. The breeds with greater mature weight were found to have greater maternal genetic effects for calving ease but negative direct genetic effects on calving ease. A negative effect of mature weight on the direct genetic effect of survival to weaning was observed. A cluster analysis was done using 17 breeds for which information existed on nine maternal traits. Regression was used to predict breed-cross-specific heterosis using genetic distance. Only five traits, birth weight, survival to weaning, cow fertility, and preweaning and postweaning growth rate had enough breed-cross-specific heterosis estimates to develop a prediction model. The breed biological values estimated provide a basis to predict the biological value of crossbred suckler cows and their offspring.     

Correlated responses of pre- and postweaning growth and backfat thickness to six generations of selection for ovulation rate or prenatal survival in French Large White pigs

Correlated effects of selection for components of litter size on growth and backfat thickness were estimated using data from 3 pig lines derived from the same base population of Large White. Two lines were selected for 6 generations on either high ovulation rate at puberty (OR) or high prenatal survival corrected for ovulation rate in the first 2 parities (PS). The third line was an unselected control (C). Genetic parameters for individual piglet BW at birth (IWB); at 3 wk of age (IW3W); and at weaning (IWW); ADG from birth to weaning (ADGBW), from weaning to 10 wk of age (ADGPW), and from 25 to 90 kg of BW (ADGT); and age (AGET) and average backfat thickness (ABT) at 90 kg of BW were estimated using REML methodology applied to a multivariate animal model. In addition to fixed effects, the model included the common environment of birth litter, as well as direct and maternal additive genetic effects as random effects. Genetic trends were estimated by computing differences between OR or PS and C lines at each generation using both least squares (LS) and mixed model (MM) methodology. Average genetic trends for direct and maternal effects were computed by regressing line differences on generation number. Estimates of direct and maternal heritabilities were, respectively, 0.10, 0.12, 0.20, 0.24, and 0.41, and 0.17, 0.33, 0.32, 0.41, and 0.21 (SE = 0.03 to 0.04) for IWB, IW3W, IWW, ADGBW, and ADGPW. Genetic correlations between direct and maternal effects were moderately negative for IWB (-0.21 +/- 0.18), but larger for the 4 other traits (-0.59 to -0.74). Maternal effects were nonsignificant and were removed from the final analyses of ADGT, AGET, and ABT. Direct heritability estimates were 0.34, 0.46, and 0.21 (SE = 0.03 to 0.05) for ADGT, AGET, and ABT, respectively. Direct and maternal genetic correlations of OR with performance traits were nonsignificant, with the exception of maternal correlations with IWB (-0.28 +/- 0.13) and ADGPW (0.23 +/- 0.11) and direct correlation with AGET (-0.23 +/- 0.09). Prenatal survival also had low direct but moderate to strong maternal genetic correlations (-0.34 to -0.65) with performance traits. The only significant genetic trends were a negative maternal trend for IBW in the OR line and favorable direct trends for postweaning growth (ADGT and AGET) in both lines. Selection for components of litter size has limited effects on growth and backfat thickness, although it slightly reduces birth weight and improves postweaning growth.     

Age of dam and sex of calf adjustments and genetic parameters for gestation length in Charolais cattle

To estimate adjustment factors and genetic parameters for gestation length (GES), AI and calving date records (n = 40,356) were extracted from the Canadian Charolais Association field database. The average time from AI to calving date was 285.2 d (SD = 4.49 d) and ranged from 274 to 296 d. Fixed effects were sex of calf, age of dam (2, 3, 4, 5 to 10, > or = 11 yr), and gestation contemporary group (year of birth x herd of origin). Variance components were estimated using REML and 4 animal models (n = 84,332) containing from 0 to 3 random maternal effects. Model 1 (M1) contained only direct genetic effects. Model 2 (M2) was G1 plus maternal genetic effects with the direct x maternal genetic covariance constrained to zero, and model 3 (M3) was G2 without the covariance constraint. Model 4 (M4) extended G3 to include a random maternal permanent environmental effect. Direct heritability estimates were high and similar among all models (0.61 to 0.64), and maternal heritability estimates were low, ranging from 0.01 (M2) to 0.09 (M3). Likelihood ratio tests and parameter estimates suggested that M4 was the most appropriate (P < 0.05) model. With M4, phenotypic variance (18.35 d2) was partitioned into direct and maternal genetic, and maternal permanent environmental components (hd2 = 0.64 +/- 0.04, hm2 = 0.07 +/- 0.01, r(d,m) = -0.37 +/- 0.06, and c2 = 0.03 +/- 0.01, respectively). Linear contrasts were used to estimate that bull calves gestated 1.26 d longer (P < 0.02) than heifers, and adjustments to a mature equivalent (5 to 10 yr old) age of dam were 1.49 (P < 0.01), 0.56 (P < 0.01), 0.33 (P < 0.01), and -0.24 (P < 0.14) d for GES records of calves born to 2-, 3-, 4-, and > or = 11-yr-old cows, respectively. Bivariate animal models were used to estimate genetic parameters for GES with birth and adjusted 205-d weaning weights, and postweaning gain. Direct GES was positively correlated with direct birth weight (BWT; 0.34 +/- 0.04) but negatively correlated with maternal BWT (-0.20 +/- 0.07). Maternal GES had a low, negative genetic correlation with direct BWT (-0.15 +/- 0.05) but a high and positive genetic correlation with maternal BWT (0.62 +/- 0.07). Generally, GES had near-zero genetic correlations with direct and maternal weaning weights. Results suggest that important genetic associations exist for GES with BWT, but genetic correlations with weaning weight and postweaning gain were less important.     

An analysis of body weights and maturing patterns in western range ewes

The objectives were to determine the association of maturing patterns with growth rates and body weights and to estimate heritabilities and genetic and phenotypic correlations among these characters of sheep. Records of 1,109 range ewes from the Montana Agricultural Experiment Station Red Bluff Research Ranch at Norris were analyzed. Body weight and degree of maturity of body weight at birth, weaning, 12 mo of age, 18 mo of age and maturity (body weight only), and absolute growth rate (AGR), absolute maturing rate (AMR) and relative growth rate (RGR) over various age intervals were examined. Mature weight, required to calculate degree of maturity and AMR, was estimated by the average of the fall weights taken at 42, 54, 66 and 78 mo of age. Heritability estimates were .53 +/- .12 for mature weight and from .26 to .46 for immature weights. Genetic correlations among body weights at all ages were positive and generally large between immature weights and mature weights. Heritability estimates for degree of maturity ranged from .63 +/- .12 at 12 mo of age to .19 +/- .11 at 30 mo of age, at which time maturity was being approached. Genetic correlations between degree of maturity and body weight at the same age were positive; however, degree of maturity at all ages was negatively correlated with mature weight. Animals more mature at any age or stage during growth tended to be more mature at later stages, to be lighter at maturity, and to grow faster and weigh more up to 12 mo of age. Heritability estimates for AGR, RGR and AMR were moderate to high and were similar for the same age intervals. Selection for any one of the measures of growth rate would tend to expand the shape of the growth curve toward heavier weights and lower degree of maturity for any interval.     

Estimation of direct, maternal, and grandmaternal genetic effects for weaning weight in several breeds of beef cattle.

Weaning weights from nine parental breeds and three composites were analyzed to estimate variance due to grandmaternal genetic effects and to compare estimates for variance due to maternal genetic effects from two different models. Number of observations ranged from 794 to 3,465 per population. Number of animals in the pedigree file ranged from 1,244 to 4,326 per population. Two single-trait animal models were used to obtain estimates of covariance components by REML using an average information method. Model 1 included random direct and maternal genetic, permanent maternal environmental, and residual environmental effects as well as fixed sex x year and age of dam effects. Model 2 in addition included random grandmaternal genetic and permanent grandmaternal environmental effects to account for maternal effects of a cow on her daughter's maternal ability. Non-zero estimates of proportion of variance due to grandmaternal effects were obtained for 7 of the 12 populations and ranged from .03 to .06. Direct heritability estimates in these populations were similar with both models. Existence of variance due to grandmaternal effects did not affect the estimates of maternal heritability (m2) or the correlation between direct and maternal genetic effects (r(am)) for Angus and Gelbvieh. For the other five populations, magnitude of estimates increased for both m2 and r(am) when estimates of variance due to grandmaternal effects were not zero. Estimates of the correlation between maternal and grandmaternal genetic effects were large and negative. These results suggest that grand-maternal effects exist in some populations, that when such effects are ignored in analyses maternal heritability may be underestimated, and that the correlation between direct and maternal genetic effects may be biased downward if grandmaternal effects are not included in the model for weaning weight of beef cattle.     

Genetic parameters for individual birth and weaning weight and for litter size of Large White pigs

Data from a French experimental herd recorded between 1990 and 1997 were used to estimate genetic parameters for individual birth and weaning weight, as well as litter size of Large White pigs using restricted maximum likelihood (REML) methodology applied to a multivariate animal model. In addition to fixed effects the model included random common environment of litter, direct and maternal additive genetic effects. The data consisted of 1928 litters including individual weight observations from 18 151 animals for birth weight and from 15 360 animals for weaning weight with 5% of animals transferred to a nurse. Estimates of direct and maternal heritability and proportion of the common environmental variance for birth weight were 0.02, 0.21 and 0.11, respectively. The corresponding values for weaning weight were 0.08, 0.16 and 0.23 and for litter size 0.22, 0.02 and 0.06, respectively. The direct and the maternal genetic correlations between birth and weaning weight were positive (0.59 and 0.76). Weak positive (negative) genetic correlations between direct effects on weight traits and maternal effects on birth weight (weaning weight) were found. Negative correlations were found between direct genetic effect for litter size and maternal genetic effects on all three traits. The negative relationship between litter size and individual weight requires a combined selection for litter size and weight.     

Genetic parameters for individual birth and weaning weight and for litter size of Large White pigs

Data from a French experimental herd recorded between 1990 and 1997 were used to estimate genetic parameters for individual birth and weaning weight, as well as litter size of Large White pigs using restricted maximum likelihood (REML) methodology applied to a multivariate animal model. In addition to fixed effects the model included random common environment of litter, direct and maternal additive genetic effects. The data consisted of 1928 litters including individual weight observations from 18151 animals for birth weight and from 15360 animals for weaning weight with 5% of animals transferred to a nurse. Estimates of direct and maternal heritability and proportion of the common environmental variance for birth weight were 0.02, 0.21 and 0.11, respectively. The corresponding values for weaning weight were 0.08, 0.16 and 0.23 and for litter size 0.22, 0.02 and 0.06, respectively. The direct and the maternal genetic correlations between birth and weaning weight were positive (0.59 and 0.76). Weak positive (negative) genetic correlations between direct effects on weight traits and maternal effects on birth weight (weaning weight) were found. Negative correlations were found between direct genetic effect for litter size and maternal genetic effects on all three traits. The negative relationship between litter size and individual weight requires a combined selection for litter size and weight.     

Estimates of direct and maternal (co)variance components as well as genetic parameters of growth traits in Nellore sheep

In the present study, (co)variance components and genetic parameters in Nellore sheep were obtained by restricted maximum likelihood (REML) method using six different animal models with various combinations of direct and maternal genetic effects for birth weight (BW), weaning weight (WW), 6-month weight (6MW), 9-month weight (9MW) and 12-month weight (YW). Evaluated records of 2075 lambs descended from 69 sires and 478 dams over a period of 8 years (2007–2014) were collected from the Livestock Research Station, Palamaner, India. Lambing year, sex of lamb, season of lambing and parity of dam were the fixed effects in the model, and ewe weight was used as a covariate. Best model for each trait was determined by log-likelihood ratio test. Direct heritability for BW, WW, 6MW, 9MW and YW were 0.08, 0.03, 0.12, 0.16 and 0.10, respectively, and their corresponding maternal heritabilities were 0.07, 0.10, 0.09, 0.08 and 0.11. The proportions of maternal permanent environment variance to phenotypic variance (Pe²) were 0.07, 0.10, 0.07, 0.06 and 0.10 for BW, WW, 6MW, 9MW and YW, respectively. The estimates of direct genetic correlations among the growth traits were positive and ranged from 0.44(BW-WW) to 0.96(YW-9MW), and the estimates of phenotypic and environmental correlations were found to be lower than those of genetic correlations. Exclusion of maternal effects in the model resulted in biased estimates of genetic parameters in Nellore sheep. Hence, to implement optimum breeding strategies for improvement of traits in Nellore sheep, maternal effects should be considered.     

Analyses of growth curves of nellore cattle by multiple-trait and random regression models

The purpose of this study was to compare estimates of genetic parameters for sequential growth of beef cattle using two models and two data sets. Growth curves of Nellore cattle were analyzed using body weights measured at ages 1 (birth weight) to 733 d. Two data samples were created, one with 71,867 records sampled from all herds (MISS), and the other with 74,601 records sampled from herds with no missing traits (NMISS). Records preadjusted to a fixed age were analyzed by a multiple-trait model (MTM), which included the effects of contemporary group, age of dam class, additive direct, additive maternal, and maternal permanent environment. Analyses were by REML, with five traits at a time. The random regression model (RRM) included the effects of age of animal, contemporary group, age of dam class, additive direct, additive maternal, permanent environment, and maternal permanent environment. All effects were modeled as cubic Legendre polynomials. These analyses were also by REML. Shapes of estimates of variances by MTM were mostly similar for both data sets for all except late ages, where estimates for MISS were less regular, and for birth weight with MISS. Genetic correlations among ages for the direct and maternal effects were less smooth with MISS. Genetic correlations between direct and maternal effects were more negative for NMISS, where few sires were maternal grandsires. Parameter estimates with RRM were similar to MTM cept that estimates of variances showed more artifacts for MISS; the estimates of additive direct-maternal correlations were more negative with both data sets and approached -1.0 for some ages with NMISS. When parameters of a growth model obtained by used for genetic evaluation, these parameters should be examined for consistency with parameters from MTM and prior information, and adjustments may be required to eliminate artifacts.     

Estimation of additive and non-additive genetic parameters for reproduction, growth and survival traits in crosses between the Moroccan D'man and Timahdite sheep breeds

Genetic breed differences, heterosis, recombination loss, and heritability for reproduction traits, lamb survival and growth traits to 90 days of age were estimated from crossing D'man and Timahdite Moroccan breeds. The crossbreeding parameters were fitted as covariates in the model of analysis. The REML method was used to estimate (co)variance components using an animal model. The first estimation of crossbreeding effects for Timahdite and D'man breeds shows that breed differences in litter traits are mainly of maternal genetic origin: +1.04 lambs, +1.88 kg, +0.60 lambs, and +2.23 kg in favour of D'man breed for litter size at lambing, litter weight at lambing, litter size at weaning, and litter weight at 90 days, respectively. The breed differences in lamb growth and survival are also of maternal genetic origin for the majority of traits studied, but in favour of the Timahdite breed: +3.48 kg, +45 g day⁻¹ and +0.19 lambs for weight at 90 days, for average daily gain between 30 and 90 days of age, and for lamb survival to 90 days, respectively. The D'man direct genetic effect was low and negative for survival and birth weight of lambs during the first month of life. All traits studied showed positive heterosis effects. Recombination loss effects were not significant. Therefore, crossbreeding of Timahdite with D'man breeds of sheep can result in an improved efficiency of production of saleable lambs. Heritability estimates were medium for litter size but low for the other reproduction traits. Direct heritabilities were low for body weights and lamb survival at 90 days and the corresponding maternal heritabilities showed, however, low to moderate estimates. For litter traits, the estimates of genetic and phenotypic correlations were positive and particularly high for genetic correlations.     

Comparison of models for estimation of genetic parameters for mature weight of Hereford cattle

Genetic parameters of mature weight are needed for effective selection and genetic evaluation. Data for estimating these parameters were collected from 1963 to 1985 and consisted of 32,018 mature weight records of 4,175 Hereford cows that were in one control and three selection lines that had been selected for weaning weight, for yearling weight, or for an index combining yearling weight and muscle score for 22 yr. Several models and subsets of the data were considered. The mature weight records consisted of a maximum of three seasonal weights taken each year, at brand clipping (February and March), before breeding (May and June), and at palpation (August and September). Heritability estimates were high (0.49 to 0.86) for all models considered, which suggests that selection to change mature weight could be effective. The model that best fit the data included maternal genetic and maternal permanent environmental effects in addition to direct genetic and direct permanent environmental effects. Estimates of direct heritability with this model ranged from 0.53 to 0.79, estimates of maternal heritability ranged from 0.09 to 0.21, and estimates of the genetic correlation between direct and maternal effects ranged from -0.16 to -0.67 for subsets of the data based on time of year that mature weight was measured. For the same subsets, estimates of the proportions of variance due to direct permanent environment and maternal permanent environment ranged from 0.00 to 0.09 and 0.00 to 0.06, respectively. Using a similar model that combined all records and included an added fixed effect of season of measurement of mature weight, direct heritability, maternal heritability, genetic correlation between direct and maternal effects, proportion of variance due to direct permanent environmental effects, and proportion of variance due to maternal permanent environmental effects were estimated to be 0.69, 0.13, -0.65, 0.00, and 0.04, respectively. Mature weight is a highly heritable trait that could be included in selection programs and maternal effects should not be ignored when analyzing mature weight data.     

Genetic parameters for growth traits in Mexican Nellore cattle

The aim of this study was to estimate genetic parameters for growth traits in Mexican Nellore cattle. A univariate animal model was used to estimate (co)variance components and genetic parameters. The traits evaluated were birth weight (BW), weaning weight (WW), and yearling weight (YW). Models used included the fixed effects of contemporary groups (herd, sex, year, and season of birth) and age of dam (linear and quadratic) as a covariate. They also included the animal, dam, and residual as random effects. Phenotypic means (SD) for BW, WW, and YW were 31.4 (1.6), 175 (32), and 333 (70) kg, respectively. Direct heritability, maternal heritability, and the genetic correlation between additive direct and maternal effects were 0.59, 0.17, and −0.90 for BW; 0.29, 0.17, and −0.90 for WW; and 0.24, 0.15, and −0.86 for YW, respectively. The results showed moderate direct and maternal heritabilities for the studied traits. The genetic correlations between direct and maternal effects were negative and high for all the traits indicating important tradeoffs between direct and maternal effects. There are significant possibilities for genetic progress for the growth traits studied if they are included in a breeding program considering these associations.     

Genetic parameter estimation for pre- and post-weaning traits in Brahman cattle in Brazil

Beef cattle producers in Brazil use body weight traits as breeding program selection criteria due to their great economic importance. The objectives of this study were to evaluate different animal models, estimate genetic parameters, and define the most fitting model for Brahman cattle body weight standardized at 120 (BW120), 210 (BW210), 365 (BW365), 450 (BW450), and 550 (BW550) days of age. To estimate genetic parameters, single-, two-, and multi-trait analyses were performed using the animal model. The likelihood ratio test was verified between all models. For BW120 and BW210, additive direct genetic, maternal genetic, maternal permanent environment, and residual effects were considered, while for BW365 and BW450, additive direct genetic, maternal genetic, and residual effects were considered. Finally, for BW550, additive direct genetic and residual effects were considered. Estimates of direct heritability for BW120 were similar in all analyses; however, for the other traits, multi-trait analysis resulted in higher estimates. The maternal heritability and proportion of maternal permanent environmental variance to total variance were minimal in multi-trait analyses. Genetic, environmental, and phenotypic correlations were of high magnitude between all traits. Multi-trait analyses would aid in the parameter estimation for body weight at older ages because they are usually affected by a lower number of animals with phenotypic information due to culling and mortality.     

Effects of sire misidentification on estimates of genetic parameters for birth and weaning weights in Hereford cattle

Birth weights (4,155) and weaning weights (3,884) of Line 1 Herefords collected at the Fort Keogh Livestock and Range Research Laboratory in Miles City, MT, between the years of 1935 to 1989 were available. To study the effect of misidentification on estimates of genetic parameters, the sire identification of calf was randomly replaced by the identification of another sire based on the fraction of progeny each sire contributed to a yearly calf crop. Misidentification rates ranged from 5 to 50% with increments of 5%. For each rate of misidentification, 100 replicates were obtained and analyzed with single-trait and two-trait analyses with a restricted maximum likelihood (REML) algorithm. Two different models were used. Both models contained year x sex combinations and ages of dam as fixed effects, calendar birth date as a fixed covariate, and random animal and maternal genetic effects and maternal permanent environment effects. Model 2 also included sire x year combinations as random effects. As the rate of misidentification increased, estimates of the direct-maternal genetic correlation increased for both traits, with both models, for all analyses. With singletrait analyses, estimates of the fraction of variance that were due to sire x year interaction effects increased slightly for birth weight (near zero) and decreased slightly (0.015 to 0.004) for weaning weight as misidentification increased. With two-trait analyses, estimates of fraction of variance that were due to sire x year effects gradually decreased for weaning weight as misidentification increased. With the two-trait analyses, and with both models, as the level of sire misidentification increased, estimates of the genetic correlation between direct effects gradually increased, and estimates of the correlation between maternal effects gradually decreased. Estimates of the direct-maternal genetic correlation were more positive with Model 2 than with Model 1 for all levels of misidentification. Results of this study indicate that misidentification of sires would severely bias estimates of genetic parameters and would reduce genetic gain from selection.     

Bayesian inference for genetic parameter estimation on growth traits for Nelore cattle in Brazil,using the Gibbs sampler

This data set consisted of over 29 245 field records from 24 herds of registered Nelore cattle born between 1980 and 1993, with calves sires by 657 sires and 12 151 dams. The records were collected in south‐eastern and midwestern Brazil and animals were raised on pasture in a tropical climate. Three growth traits were included in these analyses: 205‐ (W205), 365‐ (W365) and 550‐day (W550) weight. The linear model included fixed effects for contemporary groups (herd‐year‐season‐sex) and age of dam at calving. The model also included random effects for direct genetic, maternal genetic and maternal permanent environmental (MPE) contributions to observations. The analyses were conducted using single‐trait and multiple‐trait animal models. Variance and covariance components were estimated by restricted maximum likelihood (REML) using a derivative‐free algorithm (DFREML) for multiple traits (MTDFREML). Bayesian inference was obtained by a multiple trait Gibbs sampling algorithm (GS) for (co)variance component inference in animal models (MTGSAM). Three different sets of prior distributions for the (co)variance components were used: flat, symmetric, and sharp. The shape parameters (ν) were 0, 5 and 9, respectively. The results suggested that the shape of the prior distributions did not affect the estimates of (co)variance components. From the REML analyses, for all traits, direct heritabilities obtained from single trait analyses were smaller than those obtained from bivariate analyses and by the GS method. Estimates of genetic correlations between direct and maternal effects obtained using REML were positive but very low, indicating that genetic selection programs should consider both components jointly. GS produced similar but slightly higher estimates of genetic parameters than REML, however, the greater robustness of GS makes it the method of choice for many applications.