Maternal Heritability Estimates Research Articles

Estimates of genetic parameters for direct and maternal effects on birth weight of local sheep in United Arab Emirates

Genetic parameters for birth weight were estimated for two sets of purebred and crossbred lambs in United Arab Emirates, using animal model methods. Data were analyzed by restricted maximum likelihood (REML). Five different animal models were fitted. Model 1 considered the animal as the only random effect. Models 2 and 3 included in addition to the additive direct effect of the animal, the additive maternal and the permanent maternal environmental effects, respectively. Model 4 fitted both the additive maternal and permanent environmental effects. Model 5 was the same as model 4, except that a covariance between the direct and the maternal additive effects was included. Estimates of direct heritability were substantially higher when maternal effects were ignored. Introducing the additive maternal effect to model 2 reduced the estimate of additive heritability by 28 and 14% of σ ̂ p 2 for the purebred and crossbred lambs, respectively. Estimates of additive direct and additive maternal heritabilities with model 4 were 0.10 and 0.33, and 0.45 and 0.10 for purebred and crossbred lambs, respectively. The correlation between direct and maternal genetic effects for the combined (purebred+crossbred lambs) data set was large and negative. These results indicate that in addition to additive direct effect, additive maternal effect for birth weight was important.

Estimates of covariance functions for growth from birth to 630 days of age in Nelore cattle.

Weight records of Brazilian Nelore cattle, from birth to 630 d of age, recorded every 3 mo, were analyzed using random regression models. Independent variables were Legendre polynomials of age at recording. The model of analysis included contemporary groups as fixed effects and age of dam as a linear and quadratic covariable. Mean trends were modeled through a cubic regression on orthogonal polynomials of age. Up to four sets of random regression coefficients were fitted for animals' direct and maternal, additive genetic, and permanent environmental effects. Changes in measurement error variances with age were modeled through a variance function. Orders of polynomial fit from three to six were considered, resulting in up to 77 parameters to be estimated. Models fitting random regressions modeled the pattern of variances in the data adequately, with estimates similar to those from corresponding univariate analysis. Direct heritability estimates decreased after birth and tended to be lowest at ages at which maternal effect estimates tended to be highest. Maternal heritability estimates increased after birth to a peak around 110 to 120 d of age and decreased thereafter. Additive genetic direct correlation estimates between weights at standard ages (birth, weaning, yearling, and final weight) were moderate to high and maternal genetic and environmental correlations were consistently high.

Estimação de parâmetros genéticos de características reprodutivas em suínos

Com o objetivo de estimar os parâmetros genéticos e fenotípicos de características reprodutivas de suínos, foram utilizados dados de peso da leitegada ao nascimento (PLN), peso da leitegada ajustado para 21 dias (PL21), tamanho de leitegada ao nascimento (TLN), tamanho de leitegada ao desmame (TLD) e taxa de mortalidade (TM), de três raças de suínos, Duroc, Landrace e Large White. Variâncias e covariâncias genéticas e fenotípicas foram estimadas pelo Método da Máxima Verossimilhança Restrita (REML), usando modelo que inclui os efeitos genéticos direto e materno e comum de leitegada. Estes componentes foram usados para calcular as herdabilidades direta (<img src="http:/img/fbpe/rbz/v29n6/5698fr7.gif">), materna (<img src="http:/img/fbpe/rbz/v29n6/5698fr8.gif">) e total (<img src="http:/img/fbpe/rbz/v29n6/5698fr9.gif">), o efeito comum de leitegada (c²) e as correlações genéticas e fenotípicas. As herdabilidades direta, materna e total apresentaram valores baixos a médios: 0,00 a 0,17, 0,00 a 0,14 e 0,00 a 0,15, respectivamente, destacando a importância da seleção com base nas informações de parentes para o melhoramento genético destas características. As correlações entre os efeitos genéticos aditivos direto e materno foram, de modo geral, altas e negativas, evidenciando antagonismo entre estes efeitos. As estimativas de c² foram em geral baixas para todas as características. As correlações genéticas entre PLN, PL21, TLN e TLD tenderam a ser altas e positivas, e as correlações entre estas características e TM apresentaram-se ora positivas, ora negativas.

Pre-weaning growth traits of the Hereford breed in a multibreed composite beef cattle population

Data from a multibreed composite beef cattle population, managed under intensive irrigated grazing conditions,were used to estimate direct additive heritabilities (h2a), maternal heritabilities (h2m) and maternal permanent environmental effects (c2) for birth weight (BW) and weaning weight (WW) of the calf and cow efficiency of the dam (CE: WW/dam weight0.75 x 100). Calves born between 1968 and 1993 (n = 52628) had varying levels of Hereford genes, ranging from 0% to 100%, with an average of 19.3%. Direct heritabilities, fitting unitrait models, were 0.72, 0.54 and 0.19 for BW, WW and CE, respectively, with corresponding estimates of maternal heritabilities being 0.14, 0.21 and 0.42. Genetic correlations between direct and maternal effects (ram) were negative for all three traits, varying from -0.40 to -0.65. Maternal permanent environmental effects were 0.06, 0.12 and 0.11 for BW, WW and CE, respectively. Direct breeding values and maternal breeding values for BW and WW decreased with increasing proportion of Hereford. Direct breeding value for CE increased, while maternal breeding value for CE reached a minimum value at 0.62 proportion of Hereford. (South African Journal of Animal Science, 2000, 30(3): 220-229)

Genetic studies on the South African Mutton Merino: growth traits

Genetic parameters were estimated for 36-, 42-, 50-, 100- and 150-day weight in the South African Mutton Merino breed. The direct heritability estimates obtained were 0.270, 0.366, 0.278, 0.185 and 0.115 respectively. The maternal heritability estimates for the respective weights were 0.494, 0.249, 0.129, 0.091 and 0.080. The correlation between the animal effects (direct and maternal) varied between -1.000 for 36-day weight to -0.376 for 150-day weight. Very little selection progress was made over the period (1980-1999) in the breed. (South African Journal of Animal Science, 2000, 30(3): 172-177)

Variance and covariance components for weaning weight for Herefords in three countries.

Records from the Hereford Associations of the United States (USA), Canada, and Uruguay were used to estimate genetic and phenotypic variances and covariances for weaning weight. Estimation was done using a complete animal model, relatively large data sets, and the same methodology for the three countries in order to determine whether genetic parameters for weaning weight were homogeneous across environments. Data were composed of 2,322,722, 487,661, and 102,986 edited weaning weight records for USA, Canada, and Uruguay, respectively. Ten samples were obtained from each country by eliminating data from small herds with fewer than 500 records, selecting herds at random from the entire data set after removing the small herds, and then retaining the direct-sire-connected contemporary groups within each sample. The final sample sizes ranged from 9,832 to 46,377 records. An accelerated EM-REML algorithm was used in estimating the (co)variance components in each sample. The estimates were pooled by calculating the arithmetic mean of the 10 samples from within each country. Direct and maternal (in parentheses) heritability estimates were .24 (.16), .20 (.16), and .23 (.18) for USA, Canada, and Uruguay, respectively. Maternal heritabilities reported here are nearly 50% smaller than the values currently used in national genetic evaluation for the breed, which were estimated using sire-maternal grandsire models. Covariance between direct and maternal was negative in all countries, accounting for 6, 8, and 10% of the total phenotypic variation, and the total dam effect was 32.5, 37.0, and 34.0% in USA, Canada, and Uruguay, respectively. Total heritabilities were similar among the countries, with values of .19, .19, and .17 for the three respective countries. The similarity of genetic and environmental parameters across the three countries suggests that joint genetic evaluation is feasible across environments provided that the genotype x environment interaction is negligible and can be ignored.

Estimates of direct, maternal and grandmaternal genetic effects for growth traits in Gobra cattle

Estimates of genetic parameters for birth (N = 3909), weaning (N = 3425), yearling (N = 2764) and final (N = 2144) weights were obtained from the records of Gobra cattle collected at the Centre de Recherches Zootechniques de Dahra, Senegal. Three animal models were fitted to obtain estimates by REML using an average information (AI) approach. Model 1 considered random direct, maternal genetic and maternal permanent environmental effects. In model 2, a general grandmaternal effect was added to the random effects considered in model 1, and in model 3, the general grandmaternal effect was divided into grandmaternal genetic and grandmaternal permanent environmental effects. All models allowed covariances among genetic effects. The inclusion of grandmaternal effects in models 2 and 3 did not change the estimates of the genetic parameters compared to model 1. Variances attributable to grandmaternal effects became negative and were set close to zero, except for yearling weight for which grandmaternal heritability was 0.03 ± 0.03. The estimates for direct and maternal heritabilities were, respectively, 0.08 ± 0.03 and 0.03 ± 0.02 for birth, 0.20 ± 0.05 and 0.21 ± 0.05 for weaning, 0.26 ± 0.07 and 0.16 ± 0.07 for yearling and 0.14 ± 0.06 and 0.16 ± 0.06 for final weights. The estimates of the genetic correlation between direct and maternal effects for birth, weaning, yearling and final weights were -0.17 ± 0.40, -0.58 ± 0.32, -0.52 ± 0.34 and -0.34 ± 0.37, respectively. For yearling weight with grandmaternal heritability estimated to be only 0.03, model 3 gave estimates of the genetic correlation between direct and grandmaternal effects and between maternal and grandmaternal effects of 0.28 ± 0.48 and -0.33 ± 0.67, respectively. Estimates of direct and maternal heritabilities were unchanged when grandmaternal effects were not included in the model.

Genetic parameters for growth traits for a composite terminal sire breed of sheep.

Records of 9,055 lambs from a composite population originating from crossing Columbia rams to Hampshire x Suffolk ewes at the U.S. Meat Animal Research Center were used to estimate genetic parameters among growth traits. Traits analyzed were weights at birth (BWT), weaning (7 wk, WWT), 19 mo (W19), and 31 mo (W31) and postweaning ADG from 9 to 18 or 19 wk of age. The ADG was also divided into daily gain of males (DGM) and daily gain of females (DGF). These two traits were analyzed with W19 and with W31 in three-trait analyses. (Co)variance components were estimated with REML for an animal model that included fixed effects of sex, age of dam, type of birth or rearing, and contemporary group. Random effects were direct and maternal genetic of animal and dam with genetic covariance, maternal permanent environmental, and random residual. Estimates of direct heritability were .09, .09, .35, .44, .19, .16, and .23 for BWT, WWT, W19, W31, ADG, DGM, and DGF, respectively. Estimates of maternal permanent environmental variance as a proportion of phenotypic variance were .09, .12, .03, .03, .03, .06, and .02, respectively. Estimates of maternal heritability were .17 and .09 for BWT and WWT and .01 to .03 for other traits. Estimates of genetic correlations were large among W19, W31, and ADG (.69 to .97), small between BWT and W31 or ADG, and moderate for other pairs of traits (.32 to .45). The estimate of genetic correlation between DGM and DGF was .94, and the correlation between maternal permanent environmental effects for these traits was .56. For the three-trait analyses, the genetic correlations of DGM and DGF with W19 were .69 and .82 and with W31 were .67 and .67, respectively. Results show that models for genetic evaluation for BWT and WWT should include maternal genetic effects. Estimates of genetic correlations show that selection for ADG in either sex can be from records of either sex (DGM or DGF) and that selection for daily gain will result in increases in mature weight but that BWT is not correlated with weight at 31 mo.

Variance components and breeding values for growth traits from different statistical models.

Estimates of genetic parameters resulting from various analytical models for birth weight (BWT, n = 4,155), 205-d weight (WWT, n = 3,884), and 365-d weight (YWT, n = 3,476) were compared. Data consisted of records for Line 1 Hereford cattle selected for postweaning growth from 1934 to 1989 at ARS-USDA, Miles City, MT. Twelve models were compared. Model 1 included fixed effects of year, sex, age of dam; covariates for birth day and inbreeding coefficients of animal and of dam; and random animal genetic and residual effects. Model 2 was the same as Model 1 but ignored inbreeding coefficients. Model 3 was the same as Model 1 and included random maternal genetic effects with covariance between direct and maternal genetic effects, and maternal permanent environmental effects. Model 4 was the same as Model 3 but ignored inbreeding. Model 5 was the same as Model 1 but with a random sire effect instead of animal genetic effect. Model 6 was the same as Model 5 but ignored inbreeding. Model 7 was a sire model that considered relationships among males. Model 8 was a sire model, assuming sires to be unrelated, but with dam effects as uncorrelated random effects to account for maternal effects. Model 9 was a sire and dam model but with relationships to account for direct and maternal genetic effects; dams also were included as uncorrelated random effects to account for maternal permanent environmental effects. Model 10 was a sire model with maternal grandsire and dam effects all as uncorrelated random effects. Model 11 was a sire and maternal grandsire model, with dams as uncorrelated random effects but with sires and maternal grandsires assumed to be related using male relationships. Model 12 was the same as Model 11 but with all pedigree relationships from the full animal model for sires and maternal grandsires. Rankings on predictions of breeding values were the same regardless of whether inbreeding coefficients for animal and dam were included in the models. Heritability estimates were similar regardless of whether inbreeding effects were in the model. Models 3 and 9 best fit the data for estimation of variances and covariances for direct, maternal genetic, and permanent environmental effects. Other models resulted in changes in ranking for predicted breeding values and for estimates of direct and maternal heritability. Heritability estimates of direct effects were smallest with sire and sire-maternal grandsire models.

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 direct and maternal effects on weights and ultrasonic muscle and fat depth of lambs

Genetic parameters were estimated for liveweights, total weight gains and ultrasonic muscle and fat depth of lambs at two different ages using a single trait animal model including direct and maternal genetic effect, and an environmental effect. Records of 972 lambs descending from 60 rams and 295 ewes were analysed by DFREML procedures. The approximate sampling correlation between the estimates indicated that the variance components of the maternal genetic effect and the covariance between the direct and maternal genetic effects were the most difficult parameters to estimate precisely. The correlation between the direct and maternal genetic effects was close to zero (−0.10–0.04) for all traits. Direct heritability estimates for weight declined slightly according to age from 0.22 at birth to 0.12 at weaning. The heritability estimate on maternal effect was very high for birth weight (0.42), and slightly lower for pre-weaning weight (0.14) than for weaning weight (0.17). The direct and maternal heritability estimates for ultrasonic measurements were generally low, except for the direct heritability for muscle depth at weaning (0.32). The results indicate that selection for maternal ability will not be more efficient by including pre-weaning traits in the selection index.

Estimates of genetic parameters for growth traits of Gobra cattle

AbstractEstimates of (co)variance components and genetic parameters were obtained for birth (no. = 3909), weaning (no. = 3425), yearling (no. = 2763), and final weight (no. = 2142) for Gobra cattle at the Centre de Recherches Zootechniques de Dahra (Senegal), using single trait animal models. Data were analysed by restricted maximum likelihood. Four different animal models were fitted for each trait. Model 1 considered the animal as the only random effect. Model 2 included in addition to the additive direct effect of the animal, the environmental effect due to the dam. Model 3 added the maternal additive genetic effects and allowed a covariance between the direct and maternal genetic effects. Model 4 fitted both maternal genetic and permanent environmental effects. Inclusion of both types of maternal effects (genetic and environmental) provided a better fit for birth and weaning weights than models with one maternal effect only. For yearling and final weights, the improvement was not significant. Important maternal effects werefound for all traits. Estimates of direct heritabilities were substantially higher when maternal effects were ignored. Estimates of direct and maternal heritabilities with model 4 were 0·07 (s.e. 0·03) and 0·04 (s.e. 0·02), 0·20 (s.e. 0·05) and 0·21 (s.e. 0.05), 0·24 (s.e. 0·07) and 0·21 (s.e. 0·06), and 0·14 (s.e. 0·06) and 0.16 (s.e. 0·06) for birth, weaning, yearling and final weights, respectively. Correlations between direct and maternal genetic effects were negative for all traits, and large for weaning and yearling weights with estimates of -0·61 (s.e. 0·33) and -0·50 (s.e. 0·31), respectively. There was a significant positive linear phenotypic trend for weaning and yearling weights. Linear trends for additive direct and maternal breeding values were not significant for any trait except maternal breeding value for yearling weight.

Familial resemblance for VO2max in the sedentary state: the HERITAGE family study.

This study investigates the familial resemblance of maximal oxygen uptake (VO2max) based on data from 86 nuclear families of Caucasian descent participating in the HERITAGE Family Study. In the current study, VO2max was measured twice on a cycle ergometer in 429 sedentary individuals (170 parents and 259 of their offspring), aged between 16 and 65 yr. The VO2max was adjusted by regression procedures for the effects of 1) age and sex; 2) age, sex, and body mass; and 3) age, sex, body mass, fat mass, and fat-free mass, as determined by underwater weighing. Evidence for significant familial resemblance was observed for each of the three VO2max phenotypes. Spouse, sibling, and parent-offspring correlations were significant, suggesting that both genetic and environmental factors contribute to the familial resemblance for VO2max. Maximal heritability estimates were at least 50%, a value inflated to an undetermined degree by nongenetic factors. The hypothesis of maternal inheritance, with the father's contribution being environmental, was also found to fit the data with estimates of maternal heritability, potentially associated in part with mitochondrial inheritance, reaching about 30%. These results suggest that genetic and nongenetic factors as well as maternal influences contribute to the familial aggregation of VO2max in sedentary individuals.

Genetic parameters for body weight, fleece weight and fibre diameter in South African Angora goats

Abstract Data obtained through the Angora goat performance testing pilot scheme, run by the Department of Agriculture at the Grootfontein Agricultural Development Institute, were analyzed. Data of kids born from 1990 until 1993 in 17 studs were used in the analysis. Traits analyzed were body weight (BW; n = 6240), greasy fleece weight (FW; n = 6239) and mean fibre diameter (FD; n = 6195). Heritability estimates were obtained for each trait employing REML-procedures under univariate animal models. By ignoring or including maternal genetic or environmental effects, four different models of analysis were fitted for each trait. Log likelihood ratio tests indicated that the model including a direct as well as a maternal genetic effect was the most suitable model for all traits. For the estimation of correlations between traits, bivariate analysis was carried out fitting direct effects only. Direct heritability estimates for BW [0.292 (with SE 0.047)] and FD [0.257 (0.046)] were higher than that estimated for FW [0.192 (0.038)]. Maternal heritability estimates of 0.090 (0.071), 0.049 (0.075) and 0.083 (0.068) were obtained for BW, FW and FD, respectively. Positive phenotypic correlations were obtained between BW and FW [0.572 (0.010)], BW and FD [0.548 (0.010)] and FW and FD [0.568 (0.010)]. Estimates of genetic correlations were 0.668 (0.058) between BW and FW, 0.558 (0.057) between BW and FD and 0.551 (0.068) between FW and FD.

REML estimates of variance and covariance components for production traits in Australian Merino sheep, using an animal model. 1. Body weight from birth to 22 months

Variance components for direct additive genetic, maternal additive genetic, and maternal environmental effects, and the covariance between direct and maternal additive genetic effects, were estimated by restricted maximum likelihood (REML) procedures, using an animal model, for body weight between birth and 22 months of age in Australian Merino sheep. Direct heritability was estimated to be 0.30 for birth weight, 0.28 for weaning weight, 0.24 for body weight at 10 months, 0.34 for body weight at 16 months, and 0.34 for body weight at 22 months. Maternal heritability estimates were 0.29, 0.41, 0.14, 0.07, and 0.07 for the same performances, respectively. Our results suggested that for birth weight and weaning weight, maternal additive genetic effects and the covariance between direct and maternal additive genetic effects were important. Following weaning, maternal additive genetic effects were the only significant maternal effects. Genetic correlations between direct and maternal additive effects were -0.43, -0.59, and -0.29 for birth weight, weaning weight, and body weight at 10 months, respectively. Direct and maternal additive genetic correlations between birth weight and body weight performances at later ages were positive and moderate, ranging from 0.17 to 0.52 and from 0.06 to 0.65, respectively, whereas they were positive and high between weaning weight and later weights, ranging from 0.59 to 0.77 and from 0.61 to 0.85, respectively. A carry-over of maternal influence after weaning was shown. Early (indirect) selection for body weight at weaning or 10 months will achieve a substantial proportion (between 53 and 81%) of direct response for performance at later ages (16 and 22 months).

Direct and maternal (co) variance components and heritability estimates for body weight at different ages and fleece traits in Afrino sheep

Abstract Data, consisting of 4325 lamb records, the progeny of 146 sires and 946 dams, collected on the Carnarvon Afrino flock over the period 1975 to 1992, were used for this study. Variance components resulting from direct additive genetic effects, maternal additive genetic effects, maternal permanent environmental effects, as well as the relationship between direct and maternal effects for birth weight, monthly body weight from weaning at 4 months to 12 months of age, 18 month body weight, 16 month clean fleece weight and 16 month mean fibre diameter were estimated by REML procedures. By ignoring or including maternal genetic or environmental effects, five different models of analysis were fitted in order to determine the most effective model for each trait. The direct heritability estimate for body weight increased from birth (0.22 ± 0.04) up to 8 months of age (0.59 ± 0.06), where it seemed to stabilise. Maternal heritability estimates for body weight, on the other hand, increased from birth (0.09 ± 0.04) to 5 months of age (0.17 ± 0.02), whereafter it decreased gradually. The maternal permanent environmental effect was significant only for birth weight (0.12 ± 0.03). Direct heritability estimates of 0.62 ± 0.04 and 0.73 ± 0.03 were obtained for clean fleece weight and mean fibre diameter, respectively. Maternal effects had no significant influence on clean fleece weight or mean fibre diameter.

Effects of dietary energy planes on growth and heritability estimates for postweaning growth traits in young beef bulls

Records of young AN and young HE bulls were analyzed to evaluate the influences of dietary energy planes on growth and heritability estimates of growth traits during 168-d postweaning test. Estimates of h2a for end of test weight (WT168), average daily gain on test (ADG 0–168) and relative growth rate on test (RGR 0–168) were much higher in the MED line than in the HED line. Between lines, maternal heritability estimates (h2m) for WT0 and ADG 0–168 were similar. Estimates of h2m for WT168 was much higher in the HED line than in the MED line. All direct-maternal genetic correlations (ram) were negative. These results may indicate that the antagonism between direct and maternal genetic effects for postweaning growth traits in the MED line was much less than that in the HED line. Key words: Beef cattle, energy plane, growth, heritability

Estimation of non-additive genetic variances in three synthetic lines of beef cattle using an animal model2

Dominance and additive x additive genetic variances were estimated for birth and weaning traits of calves from three synthetic lines of beef cattle differing in mature size. Data consisted of 3,992 and 2,877 records from lines of small-, medium-, and large-framed calves in each of two research herds located at Rhodes and McNay, IA, respectively. Variance components were estimated separately by herd and line for birth weight (BWT), birth hip height (BH), 205-d weight (WW), and 205-d hip height (WH) by derivative-free REML with an animal model. Model 1 included fixed effects of year, sex, and age of dam. Random effects were additive direct (a) and additive maternal (m) genetic with covariance (a,m), maternal permanent environmental, and residual. Model 2 also included dominance (d) and model 3 included dominance plus additive x additive (a:a) effects. In general, only slight changes occurred in other variance components estimates when day was included in Model 2. However, large estimates of additive x additive genetic variances obtained with Model 3 for 4 out of 24 analyses were associated with reductions in estimates of direct additive variances. Direct (maternal) heritability estimates averaged across herd-line combinations with Model 2 were .53(.11), .42(.04), .27(.12), and .35(.04) for BWT, BH, WW, and WH, respectively. Corresponding covariance (a,m) estimates as fractions of phenotypic variance (sigma p2) were .00, .01, .01, and .06, respectively. For maternal permanent environmental effects in Model 2, average estimates of variances as fractions of sigma p2 across herd-line combinations were .03, .00, .05, and .02, for BW, BH, WW, and WH, respectively. Dominance effects explained, on average, 18, 26, 28, and 11% of total variance for BWT, BH, WW, and WH, respectively. Most of the estimates for additive x additive variances were negligible, except for one data set for BWT, two for BH, and one for WH, where the relative estimates of this component were high (.21 to .45). These results suggest that most of the non-additive genetic variance in the traits studied is accounted for by dominance genetic effects.

Maternal effects for growth traits in beef cattle

Estimates of direct and maternal heritabilities, the genetic correlation between direct and maternal additive effects, and the permanent environmental variance as a percentage of the phenotypic variance ( c 2) were reported for weights of beef cattle at birth, weaning, yearling and 18 months. The data consisted of one Hereford and two Angus weight selection herds, analysed separately, recorded from 1969 to 1987 with a grand total of 7291 records. A univariate animal model was used. Direct and maternal heritabilities averaged 0.30 and 0.07 respectively for birth weight, 0.14 and 0.13 for weaning weight, 0.29 and 0.04 for yearling weight, and 0.32 and 0.04 for 18-month weight, whilst c 2 terms averaged 0.05, 0.15, 0.03 and 0.01 respectively. Genetic correlations between direct and maternal genetic effects in the Angus data averaged 0.20, 0.03, 0.09 and 0.27, respectively. Genetic correlations in the Hereford data were 0.37, −0.35, 0.97 and 0.95, respectively. Animal models which ignored maternal effects tended to overestimate direct heritability.

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.