Maternal Breed Research Articles

Genotype × Environment Interactions in Horn Fly (Diptera:Muscidae) Resistance in Angus, Brahman, and F1 Reciprocal Crossbred Cows on Common Bermudagrass or Endophyte-Infected Tail Fescue

Weekly horn fly (Diptera:Muscidae) counts were recorded on 125 Angus, Brahman, and F1 reciprocal crossbred heifers grazing endophyte-infected tall fescue or common bermudagrass during the fly seasons in 1990 and 1991. Direct heterosis, maternal breed, and direct breed effects for average fly infestation were estimated as linear contrasts among sire breed × dam breed least squares means in these heifers. Heterosis differed between forages (P<.05) and averaged –16.8 (P<.01) and –.9 (P=.88) flies per head per d on common bermudagrass and tall fescue, respectively. Maternal breed effects were not significant on either forage. Direct breed effects favored the Brahman, were larger on common bermudagrass compared to tall fescue (P<. 10), and averaged –213.0 (P<.01) flies per head per d on common bermudagrass and –167.5 (P<.01) flies per head per d on tall fescue. The results suggested that utilization of heterosis and direct breed effects in Bos indicus × Bos taurus crossbreeding systems was effective in substantially lowering horn fly infestation, but the efficacy of the genetic effects depended on the forage environment.

Efficiency of an approximate animal model for maternal and direct genetic effects of litter size in swine

A simulated population of 120 sows and 24 boars in service per year was used to compare genetic evaluations for first-parity litter size and selection response when approximate and complete animal models were used. The complete animal model included maternal and direct effects. The approximate model did not account for covariances between maternal breeding values, or between maternal and direct breeding values, but included a random litter effect of birth of sow. After 10 yr of selection, the overall response (maternal plus direct) was 2.94, 1.61, and .77 pigs using the approximate model and 3.11, 1.65, and .67 pigs using the complete model with equal weighting of maternal and direct genetic effects in the aggregated breeding value for genetic correlations between maternal and direct effects of 0, -.5, and -.9, respectively. Higher reduction was obtained in direct genetic response that was 5, 8, and 19% lower using the approximate model than the complete model for genetic correlations of 0, -.5, and -.9, respectively. Use of the approximate model over 10 yr of selection resulted in a bias of estimation of direct genetic trend of .24, .54, and .48 pigs and in bias in estimated overall response (maternal plus direct) of -.49, .67, and 1.28 pigs for genetic correlations between maternal and direct effects of 0, -.5, and -.9, respectively. Bias in environmental trend estimated from year-season effects was of the same magnitude as the bias in estimated overall response but with an opposite sign. With the approximate model, maternal genetic response was due to a correlation between maternal genetic effects and direct EBV, which for an embedded trait such as maternal genetic effects occurred even when there was no correlation between their true genetic effects. Findings suggested that over the short term the approximate model can be used without substantial loss of overall response but the use of the complete model was recommended because of unbiased estimates in genetic and environmental trend and higher direct genetic response.

Fixed effects in the formation of a composite line of beef cattle: I. Experimental design and reproductive performance

Red Angus (RA) dams were mated to Charolais (C) or Tarentaise (T) sires to produce crossbred (F1) progeny. Members of the F1 generation, differing in breed direct effects, were mated to produce an F2 generation with an expected breed composition of 1/2 RA, 1/4 C, and 1/4 T. Two breed groups within the F2 generation differing in breed maternal effect ([C x RA] x [T x RA] and [T x RA] x [C x RA]) were identified separately. These breed groups were crossed to produce an F3 generation and, likewise, the two resulting F3 generation breed groups were crossed to produce an F4 generation. No distinction was made among breed groups subsequent to the F3 generation. Pregnancy rates averaged 90.9% over 11 yr, with 82.0% of cows exposed weaning a calf. Among formative generations of this composite population, F2 had greatest pregnancy, calving, and weaning rates. Age of dam significantly affected pregnancy rate, calving difficulty, and gestation length. Older cows tended to express higher pregnancy rates and longer gestation lengths than did younger cows (P < .01). Males calves had a 1.7% greater weaning rate than female calves (P < .05), but matings producing male calves had longer gestation lengths (P < .05) and were 8.5% more likely to experience calving difficulty (P < .01). Individual breed additive effects (calves from C or T sires mated to RA dams) were important for calving difficulty only (P < .05), where C-sired matings experienced greater calving difficulty. Differences between C x RA and T x RA dams, indicative of maternal breed additive effects, were not detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Fixed effects in the formation of a composite line of beef cattle: II. Pre- and postweaning growth and carcass composition

Generation, age of dam, sex of calf, and certain covariates were studied to elucidate their effect on traits related to growth and carcass characters measured on individuals from a stabilized three-breed composite (1/2 Red Angus [RA], 1/4 Charolais [C], 1/4 Tarentaise [T]). There was evidence that sires had been selected for yearling weight. Thus, an animal model was fitted to the data to estimate the effects free of bias due to selection. Differences between generations were not different from zero (P > .05) for birth weight, weaning weight, and preweaning ADG. There were few important differences between generations for carcass traits as well. This may have been caused by confounding of individual and maternal heterotic effects with direct and maternal components of the model, or the partial confounding of years, age of dam, and generation. Birth weight was curvilinear with respect to calving day (P < .01). Age of dam was important for all growth traits except postweaning ADG. In general, growth of calves increased with increasing age of dam, as did carcass weight and predicted retail product. Individual breed additive effects (differences between calves sired by C and T sires mated to RA dams) were positive for birth weight (P < .01), weaning weight (P < .05), carcass weight (P < .05), and predicted retail product (P < .05). Maternal breed additive effects (differences between calves out of C x RA or T x RA dams) were also positive for weaning weight (P < .05), carcass weight (P < .05), and fat depth (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Sire x herd interactions for weaning weight in beef cattle.

Weaning weight records of 44,357 Australian Angus calves produced by 1,020 sires in 90 herds were used to evaluate the importance of sire x herd interactions. Models fitted fixed effects of contemporary group (herd-year-date of weighing subclass), sex, calf age, and dam age and random effects of sire or of sire and sire x herd interaction using REML. Effects of standardizing the data, including sire relationships and including dam maternal breeding values (MBV) as a covariate were also investigated. Sire x herd interactions were found (P less than .05) in all cases and, in the most complete model, accounted for 3.3% of phenotypic variance. Across-herd heritabilities ranged from .19 to .28. Differential nonrandom mating among herds seemed to occur in the data. Significant sire x herd effects were observed for dam MBV, and adjustment for dam MBV yielded the smallest estimates of interaction variance and across-herd heritability. If sire x herd interactions were due only to genotype x environment interaction, within-herd heritabilities would range from .33 to .49. These estimates are larger than previously reported estimates. Thus, unreported environmental effects common to progeny of individual sires may also be involved in the observed interaction but could not be disentangled from true genotype x environment interaction effects using these data. Results of these analyses suggest that some accommodation of sire x herd interaction effects on weaning weight may be needed in beef cattle genetic evaluations, but a compelling case for development of herd-specific breeding value prediction cannot be made.

Direct and maternal breed effects on growth and milk intake of piglets: Meishan versus Dutch breeds

Cross fostering techniques were used to evaluate pre-natal (direct genetic and maternal) and post-natal (maternal) breed effects in Meishan and Dutch breeds on milk intake and growth of piglets during the suckling period and growth after weaning. Meishan as well as Dutch sows nursed mixed litters of Meishan and Dutch piglets. Birth weight of Dutch as compared to Meishan piglets was 56% higher. The effects of this birth weight difference on milk intake and growth of piglets were studied. Data on 44 mixed litters nursed by 21 Dutch and 23 Meishan sows were available. At an average birth weight difference, growth rate from birth to 21 and 21–35 d was 25 and 31% higher for Dutch than for Meishan piglets respectively, while milk intake per piglet at days 13 and 30 of lactation was 38 and 36% higher, respectively. Differences between Dutch and Meishan sows were small. Higher growth during the suckling period of Dutch as compared to Meishan piglets was mainly caused by their higher birth weight. Results indicate that Meishan sows have good maternal characteristics, i.e. significantly lower piglet mortality and the ability to raise also the heavier, more demanding Dutch piglets.

Bayesian inference about dispersion parameters of univariate mixed models with maternal effects: theoretical considerations

Summary - Mixed linear models for maternal effects include fixed and random elements, and dispersion parameters (variances and covariances). In this paper a Bayesian model for inferences about such parameters is presented. The model includes a normal likelihood for the data, a flat prior for the fixed effects and a multivariate normal prior for the direct and maternal breeding values. The prior distribution for the genetic variancecovariance components is in the inverted Wishart form and the environmental components follow inverted prior distributions. The kernel of the joint posterior density of the dispersion parameters is derived in closed form. Additional numerical and analytical methods of interest that are suggested to complete a Bayesian analysis include MonteCarlo Integration, maximum entropy fit, asymptotic approximations, and the TierneyKadane approach to marginalization. maternal effect / Bayesian method / dispersion parameter

Heterose em suínos na fase de aleitamento

Visando avaliar o ganho de produtividade, advindo da heterose, no peso de suínos em fase de aleitamento, analisaram-se os pesos ao nascimento(PO), 21 dias de idade (P21) e desmama (PD) de 746leitões, sendo 201 da raça Landrace, 136 Wessex-Saddleback e 409 mestiços, pelo método dos quadrados mínimos, considerando-se, ainda, os efeitos fixos de época e ano de nascimento, ordem do parto, sexo do leitão e tamanho da leitegada, além de raças paterna e materna e suas interações. Os efeitos não genéticos tiveram influência significativa em quase todas as características. Os mestiços mostraram, em geral, pesos superiores aos puros, com estimativas de heterose de 2,6% para PO, 9,7% para P21 e 13,9% para PD, indicando a importância da herança não aditiva à medida que os leitões ficam menos dependentes de suas mães. Os efeitos de interação entre as raças paterna e materna foram cada vez maiores com o avançar da idade. Os resultados indicam haver ganho de produtividade coma utilização deste tipo de cruzamento.

Maternal breed of sire effects on postweaning performance of heifer and steer progeny: postweaning growth and carcass characteristics

Heifer and steer progeny of 2-yr-old first-cross (F1) heifers and 3- to 6-yr-old F1 cows, from Hereford dams and five sire breeds, were evaluated for postweaning feedlot growth and carcass composition. Breeds of sire of dam were Angus (A), Red Poll (RP), Tarentaise (T), Simmental (Sm), and Pinzgauer (P). Calves from 2-yr-old heifers were sired by Shorthorn, and calves from 3- to 6-yr-old dams were sired by Charolais. Breed of sire of dam was significant (P less than .05 to P less than .01) for total gain and final weight for female progeny from 2-yr-old dams. At all weights, Sm, P, and T ranked above A and RP. Progeny of A, P, Sm, and T F1 2-yr-old dams were not significantly different but were higher (P less than .05) than RP heifers in total feedlot gain. Breed of sire of dam was significant (P less than .05) for carcass weight and longissimus muscle area; T ranked highest and RP lowest. Breed was not significant for any growth traits of steer progeny of 2-yr-old dams. Breed was significant for marbling score; A ranked highest and exceeded (P less than .01) both RP and Sm steers. Breed was significant (P less than .05) for most growth traits in the heifer progeny of the 3- to 6-yr-old dams bred to Charolais sires. Heifer calves of the Sm group were heavier (P less than .05) than all other groups for most weights and total gain. For total gain, P and T were intermediate and A and RP lowest. For heifer carcass traits from 3- to 6-yr-old dams, breed was significant (P less than .05 to P less than .01) for carcass weight, longissimus muscle area, percentage of cutability, and estimated kidney, heart, and pelvic fat. Heifers from Sm-sired dams were heavier (P less than .05) than those from all other groups but ranked second to heifers from P for percentage of cutability. Marbling scores of RP heifer carcasses ranked highest of all groups. Breed was not significant (P greater than .05) for any of the weights or gains in steer progeny of 3- to 6-yr-old dams; however, the Sm and P groups ranked above A and RP for all feedlot test weights.(ABSTRACT TRUNCATED AT 250 WORDS)

Maternal breed of sire effects on postweaning performance of first-cross heifers and production characteristics of 2-year-old heifers

Postweaning growth rates from weaning to 18 mo, fall condition score, pregnancy rates, and production to 2 yr of age were evaluated in a study of Angus (A)-, Pinzgauer (P)-, Red Poll (R)-, Simmental (S)-, and Tarentaise (T)-sired females from Hereford dams. First-cross heifers from the different sire breeds did not differ (P greater than .10) in initial weight. During a 140-d feed test, S gained 98.6 kg, exceeding (P less than .05) gains of P, 92.3; A, 91.4; and R, 87.3 kg but not T, 94.1 kg. Red Poll-sired heifers weighed less at the end of the 140-d test (P less than .05) than the other crosses, which did not significantly differ from each other. No breed of sire differences were found in gain from 140 d to fall weight. Simmental-sired heifers weighed more (P less than .05) than A- and R-sired heifers at 18 mo. Breed of sire and year interacted to affect pregnancy rate of the yearling heifers when mated to Shorthorn sires for 45 d. Percentage of dystocia varied from a low of 26.3 and 28.9% for T- and A-sired heifers, respectively, to 54.4 and 60.8% for P- and S-sired heifers, respectively (P less than .05). Age of dam of heifers affected (P less than .05) weight at the different period end points but not gains after weaning. Age of dam also affected incidence of dystocia. Two-year-old heifers from young dams had more dystocia than heifers from older dams. Shorthorn-sired calves from 2-yr-old heifers with different sire breeds differed in birth weight (P less than .05) but not survival from birth to weaning, ADG from birth to weaning, weaning age, or weaning condition score. Average 200-d weight of calves from P-, S- and T-sired heifers exceeded those from A- and R-sired heifers by 10.7 kg, or 5.7%.

Effects of breed, heterosis, age of dam, litter size, and birth weight on lamb mortality1

Sources of individual plus maternal effects on lamb mortality were studied in data collected at the U.S. Meat Animal Research Center from 1980 to 1985 for paternal and maternal breeds lambing yearly and for maternal breeds lambing at 8-mo intervals. Records included 16,881 lambs born. Breeds included were Finnsheep (F), Dorset (D), Rambouillet (R), Suffolk (S), Targhee (T), Composite 1 (C1 = F/2, D/4, R/4), Composite 2 (C2 = F/2, S/4, T/4), and Composite 3 (C3 = Columbia/2, S/4, Hampshire/4), Traits analyzed were perinatal, postnatal, and total mortality to 60 d of age and postnatal respiratory, digestive, starvation, injury, and other or unknown causes of mortality. The least squares analyses included breed, year, sire within breed-year, sex, linear and quadratic season and age of dam covariates (Model 1), plus litter size (Model 2), plus birth weight (Model 3), and significant two-way interactions. Age of dam, litter size, and birth weight all had important, often quadratic, effects that differed among breeds. Models 1, 2, and 3, respectively, reduced variation by 8, 10, and 16% for perinatal, 7, 8, and 12% for postnatal, and 9, 11, and 20% for total mortality. In Model 1, breed means ranged from 3.5 to 16.2% for perinatal, 7.2 to 21.1% for postnatal, and 16.7 to 32.8% for total mortality. Respiratory and starvation problems were major causes of postnatal mortality. Heterosis for lamb survival retained in composites was 9% for C1 and 18% for C2. Mortality was 1 to 5% higher for males than for females.(ABSTRACT TRUNCATED AT 250 WORDS)

Additive and Nonadditive Genetic Effects on Milk Production in Dairy Cattle: Evidence for Major Individual Heterosis

Coefficients for individual and maternal breed composition and the expected contributions of individual and maternal heterosis and breed source of cytoplasm were assigned to 42,554 primiparous Holstein-Friesian, Jersey, and crossbred cows. The individual additive genetic breed effect influenced all milk production traits. Highly significant maternal additive genetic breed effects equivalent to 3% of the mean were identified for milk yield and milk fat percentage. Individual heterosis was highly significant for milk yield and milk fat yield. A primiparous first cross cow produced 6.1% more milk and 7.2% more milk fat than the average of straightbred cows of both breeds. For milk fat yield, the individual heterosis effect was higher than the individual additive genetic breed difference between Jersey and Holstein-Friesian. A small negative maternal heterosis and a small effect of breed source of cytoplasm were estimated for milk fat percentage. Results suggest that individual heterosis is a major genetic effect for milk yield and milk fat yield. This heterosis could be utilized through a stratified breeding scheme in which high genetic merit nucleus herds maintain genetic progress in the two straightbred populations, and commercial dairy herds employ a rotational crossbreeding scheme to take advantage of both the additive genetic progress and nonadditive genetic effects.

Genetic and environmental trends for litter size in swine.

Best linear unbiased predictors (BLUP) of breeding values for additive direct and additive maternal genetic effects were estimated from 3,944 purebred Yorkshire and Landrace first-parity litters recorded on the Quebec Record of Performance Sow Productivity Program and born between 1977 and 1987. Breeding values for gilts, dams, and sires were estimated using an individual animal model for measures of litter size of total number born (NOBN), number born alive (NOBA), and number weaned (NOWN). Environmental trends were estimated from average herd-year solutions, and genetic trends were estimated by regression of estimated breeding value on year of birth. Environmental trends were positive for all traits in both breeds but were significant only for NOWN in Landrace (.051 +/- .021 pigs/yr). Genetic trends were very small but were mainly negative for direct breeding value and combined direct and maternal breeding value. Significant estimates of genetic trends (P less than .05) were observed only within the Yorkshire breed, and these ranged from -.012 +/- .004 to .004 +/- .002 pigs/yr.

Absorption of equations for non-parents for an animal model with maternal effects and genetic groups

Rules for forming the mixed-model equations for the reduced animal model with all relationships and including maternal effects have been set out by Quaas and Pollak. They also have shown how to simplify the mixed-model equations when genetic group effects are included in the model with what has become known as the Q-P transformation. Westell has given rules for calculating the coefficients for the Q-P transformed equations that are associated with the inverse of the numerator relationship matrix and genetic group effects. Those rules can be extended to include maternal effects and genetic groups for maternal as well as direct effects. As with the rules of Quaas and Pollak for the equations for the reduced animal model, a similar set of rules can be obtained for the genetic groups model after the Q-P transformation. The rules are derived easily by examining the algebraic results of absorbing the direct and maternal breeding value equations for non-parents into the parent breeding value, group and fixed effects equations. These rules involve Westell's rules and the inverse elements of the genetic (co)variance matrix for direct and maternal additive genetic effects. The rules make calculation of breeding values for parents for models including direct and maternal genetic group effects nearly as easy as for models without genetic group effects. Back solution for direct and maternal breeding values of non-parents similarly is as simple as when genetic group effects are not in the model.

Alternative animal models with maternal effects and foster dams

Effects of foster dams can be included in genetic evaluations using animal models with maternal effects in several ways. The alternatives discussed involve minor changes in computing strategies from strategies used with reduced animal models that predict breeding values for direct and maternal effects. The easiest alternative is to assign foster dams to groups by breed and time period and add equations for fixed effects of breed-period. Random and, assumed, independent effects of foster dams can be nested in breed-period groups. If foster dams do not repeat, then those effects can be absorbed into equations for other fixed effects, additive direct breeding value and breed-period effects by slightly modifying least squares contributions to coefficients of those equations. A third alternative for foster dams of the same breed is to add breeding values for foster dams for direct and maternal effects to solution vectors for breeding values. Equations are similar to those without foster dams, except that least squares contributions to coefficient matrix and right-hand sides are to equations for maternal breeding values and nongenetic maternal effects of foster dams rather than biological dams. Relationships and covariance between direct and maternal effects contribute mixed-model coefficients to direct and maternal breeding value equations of biological dams. This alternative basically requires only larger solution vectors for direct and maternal breeding values to accommodate foster dams that might not be included. The fourth alternative includes a vector of maternal breeding values for foster dams of each breed of foster dams and would require using rules of Westell to calculate coefficients due to relationships and fixed maternal genetic groups within each breed of foster dam. These alternatives do not require much additional computational effort compared with full or reduced animal model equations when the transformation to predict breeding values is used with Westell's rules to calculate coefficients due to relationships and genetic group effects due to prior genetic selection.

Influence of variations in biological and economical parameters on beef production net returns.

Net returns were defined as a function of the monetary returns (revenue) generated by the outputs less the monetary costs generated by the variable inputs. Outputs included total weaning weights of steers and heifers, weight of cull cows and weight of open heifers. Inputs included both feed and nonfeed costs. The net returns equation was incorporated as the objective function in a linear programming model. By maximizing the objective function, the breeding system that generated the highest net returns could be identified considering certain resource constraints. Breeding systems included purebred Herefords; small rotational dual purpose (SR), utilizing the breeds Angus, Pinzgauer, Gelbvieh and Tarentaise; large rotational (LR), a three-way rotational cross with the breeds Charolais, Simmental and Maine-Anjou; and Angus-sired terminal (AL) utilizing Angus as the sire breed and LR heifers as the maternal breed. Large rotational generally produced the greatest net returns, followed by SR and either AL or HE, depending on specific resource constraints (limited feed supply or herd size), calving rates, management systems, environment, beef to feed price ratios and purchased or farm-produced (inexpensive) feed utilized. Only under the conditions of a herd size constraint and farm-produced feed did AL exceed SR in net returns. Hereford had larger net returns than LR only when the two breeding systems were evaluated in an environment assumed to be reproductively stressful to LR. Ranking of breeding systems were dependent on specific conditions and indicated that one must consider each resource constraint and environment in which cattle are expected to produce before making breeding system recommendations.

Feed intake, weaning weight and net returns comparisons for four breeding systems.

Feed intake, weaning weight and direct and maternal contributions to weaning weight were estimated for four breeding systems using data collected between 1979 and 1986 from 773 cow-calf pairs at the Elora Beef Research Centre. Breeding systems included purebred Hereford (HE), small rotational dual purpose (SR) (a four-way rotational crossing system utilizing Tarentaise, Angus, Gelbvieh and Pinzgauer breeds), large rotational beef (LR) (composed of Maine-Anjou, Simmental and Charolais) and Angus-sired large rotational beef (AL) utilizing Angus as the sire breed and LR as the maternal breed. Large rotational dams had the highest feed intakes for both dry (8.9 kg DM/d) and lactation (11.5 kg DM/d) periods. Conversely, HE calves consumed the greatest amounts of creep feed (309 kg DM), followed by AL, SR and LR. The large rotational system had the highest weaning weights (265 kg) and direct (12.3 kg greater than average of observations) and maternal (9.6 kg greater than average of observations) contributions to weaning weight, followed by AL, SR and HE for all three traits. An equation was derived for net returns that included parameters for feed intake and direct and maternal weaning weight. A linear programming model was designed to incorporate this equation as the objective function and determine the breeding system(s) that maximized net returns under various production conditions. In general, LR produced the greatest net returns, followed by SR and either AL or HE, depending on specific resource constraints (limited feed supply or herd size) included in the model.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of cytoplasmic genetic effects in beef cattle using an animal model.

Mixed model techniques were used to evaluate the importance of cytoplasmic genetic effects on beef cattle performance. Birth weight (BWT), preweaning average daily gain (ADG), weaning weight (WT205), postweaning gain (PG), ultrasonic backfat thickness (FAT) and predicted milk yield (MILK) data were collected in two herds of Hereford cattle located at Plymouth and Raleigh, North Carolina. Cytoplasmic lines were determined based on the foundation female in the maternal lineage of each animal. An animal model was used to account for all nuclear genetic variation among animals within herds. Direct breeding values were estimated for all animals with records and their parents for all traits. For MILK, permanent environmental effects were estimated for animals with multiple records. For preweaning traits, maternal breeding values and permanent maternal environmental effects also were estimated. In all analyses, F-tests for cytoplasmic effects were not significant. Probability values approached significance (P = .15 to P = .10) only for PG and FAT at Plymouth. Assumptions regarding the ratios of genetic and environmental variances and covariances had no effect on F-tests. Results contrast with earlier analyses of the same data in which nuclear genetic effects were accounted for by including sire and maternal grandsire in the statistical model. This study failed to show that cytoplasmic genetic effects were important sources of variation in performance; residual additive genetic effects were confounded with cytoplasmic lines for these herds. Because cytoplasmic sources may be regarded as founder effects, further research is needed in other populations.

Relationships between breeding values for growth of beef sires in purebreeding and crossbreeding

The studies confirmed that genetic variability for various growth traits, recorded in commercial crossbred and purebred progeny of beef sires, is slightly higher in purebred beef cattle. Breeding values were estimated according to the performance of paternal half-sib groups either purebred or commercially crossbred. Their correlation coefficients ranged from r = −0.007 to r = +0.46. The reason for these relatively low correlations may be, among other effects, due to sire × maternal breed interactions. The presence of these interactions indicates, by analogy to studies in poultry breeding, evidence of specific combining ability which should be taken into account in the selection of beef sires. The studies provide confirmatory evidence that recurrent selection of beef bulls to be used in commercial crossbreeding may be accomplished on the basis of fattening crossbred performance.

Comparison of purebred and crossbred dairy cattle for Victoria: estimation of genetic effects for yield

The yield performances of pure and crossbred dairy cattle (bred by artificial insemination) were compared using a sample of 253 422 herd-recorded Victorian dairy cattle. Pure breed groups included Holstein-Friesian (HF), Jersey (Jer), Ayrshire (Ayr), Guernsey (Gue) and Australian Illawarra Shorthorn (AIS), although numbers of Ayr, Gue and AIS were very small. The model analysed included breed additive and maternal effects, as well as heterosis and epistatic effects. Sire's Australian Breeding Value and number of generations of A1 breeding were also included. Purebred HF was found to outproduce all other purebred groups for kilograms of fat and litres of milk. Jer produced 14 kg fat (8%) and 850 L milk (22%) per lactation less than HF. Maternal breed had an effect with Jer and Gue dams being superior to HF (and other) dams. Heterosis for yield was of the order of 3% (or 5 kg fat and 110 L milk). There was no evidence of recombination loss in the crossbred groups. After combining estimates of direct, maternal and heterosis effects, HF x Jer, AIS x HF and Ayr x HF (where the first breed is breed of sire) were all found to compare equally or favourably with purebred HF for yield.