Effects of inbreeding and heterosis in Hereford females on fertility, calf survival and preweaning growth

Effects of inbreeding and heterosis and the difference between them were estimated by comparing linecross (L), topcross (T), inbred (I) and control line (C) Hereford females for reproductive and preweaning growth traits of their progeny. Inbred females (average inbreeding coefficient = 26.5%) originated from four single-sire inbred lines. Control females (average inbreeding coefficient = 6.9%) were produced by a four-sire, 60-cow line. Linecross females were produced from all possible reciprocal crosses of the I lines. Topcross females were produced by mating I bulls to C cows. Differences in pregnancy rate among these lines were not detected. Effects of maternal heterosis were positive for both prenatal and postnatal survival. The weaning rate by L females exceeded the weaning rate by I females as a result. Prenatal survival was reduced in calves from I females relative to those from C females, resulting in corresponding differences in birth and weaning rates. Differences in the magnitudes of maternal heterosis and inbreeding effects were not detected, except for birth weight. For birth weight the effect of maternal inbreeding was of greater magnitude than the effect of maternal heterosis. Within the I and C lines regressions of pregnancy rate, prenatal survival, birth rate, postnatal survival, weaning rate, weaning weight/cow exposed, birth weight and weaning weight on the inbreeding coefficients of the cows indicated significant inbreeding depression on all traits except pregnancy rate and postnatal survival.     

正反反复选择下近交对褐壳蛋鸡饲料利用率和繁殖性状的影响

本文估计了褐壳蛋鸡洛岛红(AA)和浅花苏赛克斯(BB)在正反反复选择(RRS)下的近交系数,分析了近交对选择标准饲料利用率及其相关性状和繁殖性状的影响。试验群体由两纯种及其正反交组合和相应的对照组组成。经过7个世代的RRS和近交试验,试验组AA和BB(括弧里为对照组1AA和1BB)用系谱材料计算出的平均累积近交系数分别为2.58％和3.23％(9.33和8.17%)或每代为0.43%(1.35%),用有效群体含量估计出的AA与BB的相应数值为2.91％与2.83％(5.84%与5.92％)或每代为0.42％(0.86％)。1％近交系数导致的孵化率和饲料利用率的近交衰退较严重(0.5％和0.4％),其次是产蛋性状(约0.3％),而体重和蛋重只有0.1％左右。在本研究中,通过连续7代的RRS与合适的留种率等措施,成功地将闭锁群体的近交系数控制在3%以下的低水平,消除或减轻了近交对饲料利用率等重要经济性状的不利影响。     

A diallel crossing experiment with two breeds of laying fowl

Light Sussex and Brown Leghorn flocks were concurrently bred pure and crossed in both directions for 6 years in an experiment to test for genetic interactions (“nicking”) between individual sires and dams. The traits measured in survivors to 450 days of age were (i) egg production, 126–250 days, (ii) egg production, 250–450 days, (iii) egg production, 126–450 days, (iv) mature egg weight, (v) age at sexual maturity and (vi) pullet weight at 18 weeks.

There was little response to selection in the primary trait, egg production to 450 days. Crossbreds showed a degree of heterosis in averages of egg production and there were consistent reciprocal differences between crossbreds in egg weight and pullet weight. It was impossible to distinguish between sex linkage and maternal effects in the determination of these differences.

Analyses of variance were complicated by the breed difference and by heterogeneity of variances, but yielded little evidence of interaction in egg production either between sires and breed of dams or between dams and sires. Some significant interactions were noted in egg weight and pullet weight. A weighted covariance technique yielded high positive correlations between purebred and crossbred sire family means, and confirmed that genetic interactions were unimportant. Thus reciprocal recurrent selection would not have been advantageous for improving egg production of crossbreds from the two flocks.     

Production benefits of the crossbreeding of indigenous and non-indigenous ducks—growing and laying period body weight and production performance

To evaluate different crosses and purebreds ducks in respect to various economic traits and to estimate different crossbreeding genetic parameters, a 3?×?3 complete diallel cross involving indigenous duck (DD), Khaki Campbell (KK) and White Pekin (WW) were used to produce three purebreds (DD, KK, WW) three crossbreds (DK, DW, KW) and three reciprocals (KD, WD, WK). A total of 609 ducklings produced were reared on deep litter and the females (316 in number) were evaluated for growing and laying period body weight along with the production performance traits. Different crossbreeding genetic parameters were estimated for different traits. All the traits in respect to body weight gain during growing and laying period and different production traits including laying house mortality rate showed significant (p?≤?0.05) difference between different genetic groups. In general, crossbreds perform better than the purebreds for most of the traits studied. General combining ability (GCA), specific combining ability (SCA) and reciprocal effect (RE) were significant (p?≤?0.01) for body weight and production traits. Egg weight showed significant (p?≤?0.01) difference in respect to GCA, SCA and RE for all the ages of measurement except RE for 30th week egg weight. Laying period mortality rate was only significant (p?≤?0.05) for SCA. Most of the crossbreds recorded heterosis rate in desirable direction for majority of the traits. Overall results revealed that the crossbreds perform well in respect to different traits than the purebreds and may be used to take advantage of heterosis. DW performs well in respect to majority of the traits measured and is of importance for commercial exploitation. Further, pure line selection with development of specialised sire and dam line followed by crossing may be of importance to enhance the performances in the crosses.     

Postpartum performance in a diallel cross among lines of mice selected for litter size and body weight

Postpartum dam performance was studied in a complete diallel design involving five lines of mice. The selection criterion in each line was: large litter size at birth (L+); large 6-wk body weight (W+); an index for large litter size and small 6-wk body weight (L+W-); the complementary index (L-W+) and random (K). Females from the five lines and 20 reciprocal F1 crosses were mated to sires of a randomly selected control line (CC). Correlated responses in average direct genetic and average maternal genetic effects for dam body weight and litter size at parturition persisted throughout lactation, indicating important pleiotropic effects. Major correlated responses occurred for litter weight, feed intake and litter feed efficiency, primarily due to average direct genetic effects. Using general combining ability and net line effects as criteria for choosing among lines, L+ had a distinct advantage if the objective was to increase litter size in a crossing program. If the objective was to maximize litter weaning weight, then W+ would be favored for net line effects, while L+ and W+ would be about equivalent for general combining ability. None of the lines had an advantage for litter feed efficiency. Direct heterosis for dam weight at 12 and 21 d of lactation averaged 2.7 and 1.9%, while for litter size the respective averages were 7.4 and 7.3%. The W+ X L+W- cross exhibited overdominance for litter size. Direct heterosis was moderate for feed intake and litter weight, but was negligible for litter feed efficiency because of the mathematical relationship among the three traits. Maternal heterosis for preweaning progeny growth was suppressed because of heterosis for litter size in the dam. Grand-maternal effects on growth of the young were small and would not be an important consideration in choosing among these lines in a crossbreeding program.     

Maternal heterosis and grandmaternal effects in beef cattle: preweaning traits

Crossbred progeny from females, 3 yr old and older, representing Brown Swiss (B), Red Poll (R), Hereford (H) and Angus (A) maternal grandsires and maternal granddams in a diallel crossing experiment were evaluated to estimate breed mean maternal heterosis (mean hMi) for each breed, maternal heterosis for specific breed cross females (hMij), average maternal heterosis for all crosses (mean hM) and breed grandmaternal effects (gM'i) for preweaning calf traits. Estimates of mean hM were significant for birth date and weight, 200-d weight and 200-d weight/cow exposed. Even though calves with crossbred dams weighed more at birth, they did not differ from calves with straightbred dams in frequency of calving assistance. The estimates of hMij were similar for most crosses and most traits, except 200-d weight and 200-d weight/cow exposed. The largest heterotic advantage was exhibited by progeny of BH reciprocal cross females, which exceeded crossbred progeny from BB and HH females for 200-d weight/cow exposed by 35.9 kg. The smallest heterotic effect was exhibited by crossbred progeny of RA reciprocal cross females. Progeny with R maternal granddams exhibited a higher (P less than .05) live calf born and weaned percentage than progeny with H maternal granddams. Progeny with B maternal granddams were born later (P less than .05) in the calving season than progeny with R maternal granddams. Progeny with A maternal granddams exhibited a lower frequency of calving assistance than progeny with H maternal granddams, and progeny with H maternal granddams were heavier (P less than .05) at 200 d than progeny with R maternal granddams. There was a tendency for estimates of breed grandmaternal effects (gMi) to exhibit an inverse relationship with estimates of breed maternal effects (gMi).     

Genetic study of embryonic mortality in White Leghorn lines selected for egg production traits

The present study compares embryonic mortality between lines selected for different production traits, assesses the effects of inbreeding of the hen and embryo on embryonic mortality, and estimates genetic parameters of embryonic mortality. The experiment covered 10 generations of selection for increased egg number (EN), egg weight (EW), egg mass (EM) and a control line (C). The data included age at 1st egg, egg number and egg weight. Percent fertile eggs (PF), percent hatched of fertile eggs (PHF) and percent dead chick at hatch (PDH) were also recorded for the selected parents. PDH was higher in the selected lines than in the control line. Among the selected lines, the EW line had the highest embryonic mortality. Inbreeding of the hen and embryo had no significant effect on PDH in any of the lines. Estimates of heritability for PDH were 0.10+/-0.05, 0.02+/-0.02, 0.03+/-0.02 and 0.02+/-0.02 for lines EN, EW, EM and C, respectively. There was a positive genetic correlation between egg weight and PDH in line EW indicating that selection for increased egg weight was associated with high embryonic mortality. A negative genetic correlation between PDH and reproductive traits in line EN was observed, which is favourable.     

Long-term egg production and heterosis in quail lines after within-line or reciprocal recurrent selection for high early egg production

1. Four Japanese quail lines were developed using 13 generations of reciprocal recurrent (lines AA and BB) or within-line selection (lines DD and EE) for high egg number until 98 d of age. In these lines and their reciprocal crosses, egg production, egg weight and mortality were monitored for up to 21 months to evaluate the impact of selection method and line origin on long-term production and heterosis. 2. Both hen-housed total egg number (EN) and hen-day egg laying rate (ELR) were consistently lower in recurrent lines than in lines under within-line selection: after 13 months of test, the difference was -47.1 eggs for EN and -20% for ELR%, whereas mortality was similar at around 20%. 3. Line EE was the best pure line for early egg production (55.2 eggs at 98 d of age) and also gave eggs which were consistently about 2 g larger than those from line DD but it had the highest overall mortality (78.5%) of all lines. On average, line DD laid 399 eggs (EN) over the whole experiment, 84 more than Line EE. 4. Crossbreds from the 2 types of pure lines and line DD had similar patterns and rates of egg production during the whole experiment, as indicated by the similarity of the curves adjusted for those lines by using the monomolecular model for EN and the modified compartmental model for ELR. 5. However, heterosis was higher from recurrent selection lines and it increased more with time than did heterosis from within-line selection lines.     

Cumulative inbreeding in commercial White Leghorn lines under long‐term reciprocal recurrent selection

1. Cumulative inbreeding attributable to selection in a finite population after long‐term reciprocal recurrent selection (RRS) and modified RRS (MRRS) was studied in two White Leghorn lines.

2. Pedigree information was analysed for a period of 24 generations. In one generation, progeny of full‐sib, half‐sib and unrelated pure‐line as well as reciprocal cross‐line matings were produced.

3. The structure of the two pure lines, which have been consistently used as part of the commercial cross, was documented in terms of numbers of sires and dams mated to produce sons and daughters, and variance of family size. On average, 87 sires and 870 dams per generation were mated to produce offspring.

4. Cumulative inbreeding values determined from pedigree data were compared with estimates from effective population size and variation of family size.

5. The increase in average inbreeding over 23 generations was 11.9% for line A and 10.8% for line B or 0.49% per generation, based on pedigree data.

6. Estimates from family structure were slightly higher: 12.6% for line A and 12.0% for line B or 0.54% per generation.

7. The increase in inbreeding appeared to be linear and independent of the selection method (MRRS compared to RRS).     

Heterosis, maternal and direct effects in double-muscled and normal cattle: I. Reproduction and growth traits

Data from a two-breed group diallel experiment involving double-muscled (DM) and normal (N) cattle were analyzed to evaluate the importance of heterosis, maternal and direct effects for reproduction and growth traits. The DM cattle were from a composite of primarily Angus, Charolais, Galloway and Hereford breeds, and N cattle were crossbred cattle with at least 50% Hereford breeding. The data comprised a total of 491 matings and 389 calvings in four breeding seasons. Records on calving performance, calving date, calf crop born and weaned, sex ratio of progeny and weight of calves were analyzed using least squares procedures. Significant heterosis of 5 to 12% was observed for all the calf crop and growth traits, except for birth weight. Heterosis resulted in 24% reduction in the incidence of dystocia and perinatal calf mortality (P less than .05). The significant heterosis was due mainly to poor production in DM X DM crosses. The DM cows were superior (P less than .05) to N cows in reciprocal crossing (maternal effect) for all the calf crop traits, but had higher incidence of calving difficulty and a higher proportion of male progeny. Significant direct effect was observed for all the traits except calving date and sex ratio among progeny. The N sires were superior for all the calf crop traits and caused less incidence of dystocia and perinatal mortality compared with the DM sires. Significant differences were obtained between the straightbreds for all the traits except calving date. The N straightbreds were superior to the DM straightbreds for all the significant traits.     

Selection for heterosis from crossbred populations: comparison of the F3 and backcross populations

An experimental evaluation of HI-BET (heterosis inheritance backcross evaluation technique) involving the comparison of the performance of F3 and backcross (BC) families with common sires is described. These crossbred populations were derived from an F1 cross between Australorp and White Leghorn fowls with substantial heterosis for egg production variables. There was considerable evidence for the presence of a statistically significant sire family by population type interaction for survivor's total egg mass. The ranking of sires varied substantially depending upon whether they were being assessed on the performance of their F3 or their BC daughters. The BC population yielded substantially higher sire component heritability estimates for egg weight, egg production and total egg mass than did the F3 population. For the latter two traits, this improvement in the correlation between genotype and phenotype is in accordance with the expectations of HI-BET. It is concluded the HI-BET should be effective strategy for selectively focussing upon the non-additive genes that are only present in one ancestral line at a high frequency, whilst ignoring non-additive genes unique to the other ancestral line.     

Inbreeding and inbreeding depression on reproduction and production traits of White Leghorn lines selected for egg production traits.

1. The rate of inbreeding and its effect on reproduction and egg production traits were studied in White Leghorn lines selected for egg production traits. The experiment was carried out for 10 generations in a control line (C) and in lines selected for increased egg number (EN), egg weight (EW) and egg mass (EM). 2. Data were available on reproduction traits, such as percent fertile eggs (PF), percent hatched of fertile eggs (PHF) and percent hatched of total eggs set (PHT), and on egg production traits such as age at 1st egg (AFE), egg number and egg weight. 3. The rate of increase in average inbreeding per generation was 1.50, 1.24, 1.14 and 0.18% for the line EN, EW, EM and C, respectively. The effect of inbreeding on reproduction and production traits was estimated by including the inbreeding coefficient of the hen (Fh), embryo (Fe) and mate (Fs) as a partial linear regression in the model. 4. There was a significant effect of inbreeding on reproduction traits in line EW attributable to the inbreeding of the hen, embryo and mate. No such effect was observed in the other lines. 5. In all lines inbreeding tended to reduce egg number and delay sexual maturity. In general, all lines reacted differently to inbreeding.     

Genetic parameters of cross‐ and purebred poultry

Heritabilities were estimated from sire and dam components for egg production traits in four generations of two pure‐lines and their reciprocal crosses. Heritabilities in cross‐breds, as estimated from the sire components of variance, were larger than in pure‐breds for production and sexual maturity. Heritabilities estimated from dam components were larger than the sire estimates, thus indicating the presence of maternal and/or dominance effects. Again, heritabilities in cross‐breds were larger than in pure‐breds for production and sexual maturity as well as for specific gravity. Heritabilities were also estimated for disease traits in material from one generation. Cross‐line values were as large or larger than those estimated from pure‐lines but the standard errors of the estimates were quite large.

Genetic correlations were estimated between pure‐line and cross‐line performance using both sire and dam covariances. These approached unity for body weight, egg quality traits and adult mortality but were considerably less than unity for production, sexual maturity, blood spots and mortality during growth and mortality due to Marek's disease.

The possible bias due to genotype x environment interaction is discussed and it is concluded that such a bias, if present, is small, and that in spite of possible G × E interaction effect the genetic correlations between pure‐line and cross‐line performance for production and sexual maturity are less than one. The same holds true of mortality during growth and to Marek's disease although these estimates are much less precise.

The genetic correlation between pure‐breds and cross‐breds appears to decrease over the span of the five generations.

Use of cross‐line performance will permit more efficient selection for traits when the genetic correlations are much less than one.     

Inbreeding depression on growth and prolificacy traits in two lines of rabbit

Inbreeding depression in closed populations impairs animal fitness, health, and productivity. However, not all inbreeding is expected to be equally damaging. Recent inbreeding is thought to be more harmful than ancient inbreeding because selection decreases the frequency of unfavourable alleles with time. Accordingly, selection efficiency is improved by inbreeding in a process called purging. This research aimed to quantify inbreeding depression on growth and prolificacy traits in two lines of rabbits selected for just one growth (Caldes line) or prolificacy (Prat line) trait, and also to find some evidence of purging of deleterious alleles by selection. Caldes line comprised 51 generations and 124,371 animals in the pedigree. Prat line comprised 34 generations and 161,039 animals in the pedigree. The effects of old, intermediate, and new inbreeding (Fold, Fint, and Fnew), as well as total cumulated classical inbreeding (F) and 3 measurements of ancestral inbreeding (AHC, Fa.K, and Fa.B) were estimated for average daily gain (ADG), slaughter weight (SW), weaning weight (WW), born alive (BA), the total number of kits (NT), and the number of weaned kits (NW). There was a clear inbreeding depression for all growth and prolificacy traits in the Caldes line (−7.19 g/d, −0.45 kg, −0.25 kg, −6 kits, −4 kits, and −4 kits per unit of increase in F for ADG, SW, WW, BA, NT, and NW, respectively) and also in Prat line (−7.48 g/d, −0.31 kg, −0.11 kg, −4 kits, −5 kits, and −4 kits per unit of increase in F for ADG, SW, WW, BA, NT, and NW, respectively). The inbreeding partition appears to be a reliable alternative for assessing inbreeding depression and purging. Thus, for example, in the Caldes line and for ADG the regression coefficients were −7.61, −5.41, and 7.76 g/d per unit of increase in Fnew, Fint, and Fold, respectively. In addition, AHC and Fa.B may provide more accurate evidence of purging than Fa.K. This study confirms the existence of inbreeding depression for growth and prolificacy traits in both lines of rabbits and shows evidence of purging of deleterious recessive alleles involved both in growth and prolificacy, independently of the selection criteria established in the line.     

山下黑猪与鲁莱黑猪正反交F1代杂种优势的估计

旨在估计山下黑猪和鲁莱黑猪正反交F₁代杂种优势，筛选出合适的杂交方式，以提高优质肉猪的生产效率，满足人们对于优质猪肉的需求。本研究在山下黑猪（164头）和鲁莱黑猪（69头）及其正（6头山下黑猪♂×25头鲁莱黑猪♀）、反（3头鲁莱黑猪♂×35头山下黑猪♀）交4个群体中测定了生长肥育、体尺外貌（75～110 kg）、繁殖和胴体肉质（90～115 kg）4大类共43个性状，比较了这些性状在群体间的差异，并估计了正反交F₁代的杂种优势。结果表明，山下黑猪的生长肥育和体尺性状较好，鲁莱黑猪的繁殖和肉质性状较好，正反交群体介于它们之间。正交群体的繁殖性能优于反交群体，但生长肥育性能比反交差。由于这4个群体的母猪都是纯种，因此繁殖性状没有表现出明显杂种优势。除膘厚、胸椎数、45 min pH和剪切力无显著的杂种优劣势外，大部分胴体性状和肉质性状有明显的杂种劣势。生长肥育性状的杂种优势在正反交群体中的表现不一致，反交群体表现出显著杂种优势，而正交则无明显的杂种优势。本研究估计了山下黑猪和鲁莱黑猪正反交的杂种优势，为筛选山下黑猪和鲁莱黑猪的最佳杂交方式奠定基础。     

Factors affecting direct and correlated responses in a White Leghorn population under long term selection for egg number

1. Data on 13,773 pullets, the progeny of 30 to 50 sires and about 135 to 220 dams per generation of a strain of White Leghorn under long term selection for part period egg production over 16 generations, were examined. 2. Realised genetic gain per generation was highly significant for egg production (2.55 eggs), egg weight (- 0.51 g), age at sexual maturity (- 2.30 d) and 40 week body weight (- 11.73 g). 3. The significant genetic response of 4.46 to 4.72 eggs per generation was realised in the first 8 generations only, which was accompanied by a marked decline in egg weight (- 1.67 and- 0.79 g per generation) and in age at sexual maturity (- 4.63 and- 6.39 d per generation). The 20 and 40 week body weights showed significant improvement in the last 4 generations. 4. Realised heritabilities were much lower in the last 8 than in the first 8 generation. 5. The additive genetic variance for most traits, except 20 week body weight and genetic covariances of egg production with egg weight and age at sexual maturity, declined significantly. 6. Natural selection did not seem to play any major role. No appreciable change in fitness traits was observed in the selected line. 7. The time trends were non-significant for all the traits in the control line, indicating its stability over generations.     

Performance of purebred and crossbred progeny of White Leghorn and New Hampshire sires

Data from a reciprocal recurrent selection (RRS) programme involving a White Leghorn and a New Hampshire flock were analysed to determine whether there were genetic differences in the purebred population that came to expression primarily in the crossbred progeny. The RRS programme had been in use for four years. The White Leghorn flock had previously been the subject of long‐continued and intensive family selection. The New Hampshire flock was less highly selected. Egg number, egg weight and body weight were the primary traits under selection. Each year the programme involved about 10 sires and 80 females of each breed, and about 400 offspring of each type of cross.

The overall economic value of the crossbreds consistently exceeded the mid‐parent mean, the difference increased steadily during the RRS programme. Heritabilities of the various traits were higher when calculated on the basis of crossbred offspring than when calculated on the basis of purebred offspring. For egg production in the White Leghorns there was a fairly low correlation between purebred and crossbred offspring of the same male. For other traits in both breeds the correlation between purebred and crossbred offspring was moderately high. There was a significant interaction between males and breed of females for all traits and breeds, except for egg number in the New Hampshire. These results are consistent with the notion that there were genetic differences between the purebred males (particularly the White Leghorn males) that affected the production characteristics of their crossbred progeny differently than their purebred progeny.     

Yearling trait comparisons among inbred lines and selected noninbred and randomly bred control groups of Rambouillet, Targhee and Columbia ewes

Inbreeding with concurrent selection was used to develop 26 Rambouillet, 20 Targhee and 10 Columbia inbred lines of sheep. Inbreeding coefficients averaged 30, 29 and 30% for the three breeds, respectively, at the conclusion of the study. A selected noninbred control group and a randomly bred unselected control group were maintained for each breed. Yearling traits were evaluated for 545 Rambouillet, 572 Targhee and 411 Columbia yearling ewes, each belonging to one of the inbred lines or control groups. In each breed, the selected controls were generally of greatest overall merit, the unselected controls intermediate and the inbred lines of least merit. Only a few yearling traits of only a few inbred lines were superior (P less than .05) to those of their appropriate selected control groups. Selection within inbred lines was generally ineffective in offsetting inbreeding depression. However, single trait selection for traits of high heritability, notably yearling weight, clean fleece weight and staple length, appeared to compensate for inbreeding effects on those traits. Deleterious consequences of inbreeding were particularly apparent in yearling weight, average daily gain, type and condition scores, grease and clean fleece weights and index of overall merit. Inbreeding also resulted in fewer neck folds among inbreds of all three breeds. Correlations between the rankings of inbred lines at weaning and yearling ages were high for traits of higher heritability. Superiority of the selected controls in most traits was of about the same magnitude at weaning and yearling ages. In no case did the final overall merit (index value) of an inbred line of any of the three breeds significantly exceed the overall merit of its respective selected control group.     

Effect of mate selection on fuzzy selective mating criteria in closed dairy multiple ovulation and embryo transfer nucleus programs

In order to control rates of response and inbreeding, mate selection using fuzzy selective mating criteria (FMC) was investigated in adult multiple ovulation and embryo transfer nucleus schemes for dairy cattle. Stochastic simulation was used to model the closed nucleus scheme. This mate selection was examined in four alternative mating and male selection schemes: (i) a hierarchical scheme; (ii) a hierarchical sibship scheme (two males per sibship); (iii) a factorial scheme (two sires per dam); and (iv) a factorial sibship scheme (two males per sibship and two sires per dam). Genetic response and inbreeding rate tended to be reduced by increasing the trade-off parameter of FMC between the expected breeding value and inbreeding of progeny. Inbreeding rates in all schemes were reduced by reducing the variance of family size through selection and the average coancestry of mating pairs through mate allocation.     

Genetic analyses of growth, real-time ultrasound, carcass, and pork quality traits in Duroc and Landrace pigs: I. Breed effects.

Knowledge of breed effects on carcass and pork quality traits is required to develop commercial crossbreeding programs that emphasize product quality. A 2 x 2 diallel mating system involving Landrace and Duroc pigs was used to estimate individual heterosis, direct breed effects and reciprocal cross differences for post-weaning growth, real-time ultrasound, carcass, and pork quality traits. Data from 5,649 pigs and 960 carcasses representing 65 and 49 sires, respectively, were analyzed assuming animal models. Duroc-sired pigs had 2.1 cm shorter carcasses with 7.3 mm less 10th rib backfat (BF), 4.4 cm2 larger longissimus muscle area (LMA), yielded 2.1 kg more estimated fat standardized lean (FSL), gained 16.5 g more estimated lean per day of age (LDOA), and had 1.0% less water (PWAT) and 1.9% more intramuscular fat (IMF) in the longissimus muscle than did Landrace-sired pigs (P less than .01), adjusted to an off-farm live weight of 111 kg. Reciprocal cross differences were detected for BF, LMA, FSL, LDOA and for subjective marbling, firmness, and muscling scores (P less than .01). Durocsired F1 barrows had 6.3 mm less BF and 5.9 cm2 larger LMA, yielded 3.2 kg more FSL, gained 22.3 g more LDOA, and had less marbling in the longissimus muscle and heavier ham muscling than reciprocal cross barrows. Heterosis estimates (P less than .05) were 27.6 g/d (3.2%) for ADG, -5.8 d (-3.6%) for off-test age, 2.7 cm (3.4%) for carcass length, 1.5 kg (7.2%) for FSL, 14.7 g (5.7%) for LDOA, -.07 (-3.6%) for muscle color, -.5% (-13.2%) for IMF, and .3% (.3%) for PWAT. Breed effects were not detected (P greater than .10) for muscle pH, cooking loss, shear value, and water-holding capacity or for eating quality traits. Reciprocal cross differences suggest an advantage in using the Duroc as a terminal sire, but improved carcass composition and higher intramuscular fat did not seem to affect eating quality traits.