Bull Selection across Age Classes and Variable Female Reproductive Rates in an Open Nucleus Breeding Scheme for Dairy Cattle

Different bull selection strategies and female reproductive rates were simulated under various selection intensities and mating strategies in a nucleus with testing capacity of 80 cows. In all schemes, donor cows were selected after first lactation and bulls were progeny tested. In some schemes, non-progeny tested nucleus bulls could be selected. The nucleus was open on the male side but closed on the female side after nucleus born cows were available. Pedigrees of animals born outside the nucleus were sampled from the Finnish Ayrshire population. Female reproduction rate was either constant or variable. Schemes were compared according to genetic response, and risks measured by rate of inbreeding and coefficient of variation in genetic response between simulation years 5 and 20. Inclusion of one- or three-year-old bulls increased genetic response by 9% and rate of inbreeding up to 81%. Variation in female reproductive rate reduced genetic response by at most 8%. Increase in risks was averted by limiting the number of female full-sibs. Schemes with low selection intensity and factorial mating provided the best results.     

Assessing genetic gain, inbreeding, and bias attributable to different flock genetic means in alternative sheep sire referencing schemes

Flocks participating in sire referencing schemes can achieve greater genetic gains than those achievable by within-flock selection. However, requirements for joining these schemes can be prohibitive to some producers. The objectives of this study were to determine whether less restrictive schemes or schemes of shorter duration could achieve rates of gain and reduce inbreeding as efficiently as continuous sire referencing schemes (SRS) and to investigate whether bias from different genetic means could be reduced by these alternative schemes. Pedigree and performance data for a single trait with a within-flock heritability of 0.25 were simulated (50 replications) for 15 flocks with 40 to 140 ewes per flock. Founder genetic means for each flock were sampled from a normal distribution with mean 0 and SD equal to the trait's genetic SD. After 10 yr of random mating, flocks had the opportunity to join an SRS and begin selection for the simulated trait. Yearling rams were chosen as reference sires randomly from the top one-sixth of the population ranked on BLUP EBV. Every year, in each flock, 3 reference sires were mated to 10 ewes. Six sire referencing scenarios were considered, in which all flocks participated in a SRS for 1) 15 yr; 2) 5 yr before discontinuing the scheme; 3) 10 yr before discontinuing the scheme; 4) 2 out of every 3 yr; 5) 15 yr with reference sire mating by natural service; and 6) no years (no use of SRS). Ewes not mated to reference sires were mated either to their own home-bred sires exclusively or to a mixture of homebred and unrelated purchased rams of unknown merit. Genetic gain was equivalent whether the SRS used AI or natural service matings, although inbreeding was lower with natural service. Across all scenarios, genetic gain and inbreeding were greater when excess ewes were mated exclusively to homebred sires. Genetic gains without SRS were 80 to 82% lower than when the scheme operated for 15 yr, whereas inbreeding was considerably greater. Other scenarios were intermediate in both gain and inbreeding levels. In all SRS scenarios, bias in EBV attributable to differing flock genetic means rapidly decreased in the first 5 yr of sire referencing. Levels of bias did not substantially increase when flocks discontinued SRS after 5 or 10 yr, suggesting that further participation in an SRS may not be necessary to manage risk. Natural service and noncontinuous SRS are viable options to continuous AI SRS in terms of genetic gain, inbreeding, and bias reduction.     

Optimized testing schemes using nucleus progeny, adult MOET siblings, or juvenile MOET pedigrees in dairy cattle closed populations

SUMMARY: Selection response rates are predicted for nucleus progeny testing, adult multiple ovulation and embryo transfer (MOET) sib testing, and juvenile MOET pedigree testing in closed populations. Deterministic models are adapted to adjust predicted genetic gains for the effects of population size and structure, selection disequilibrium, sampling losses, and inbreeding depression. The improvement schemes were optimized for different numbers of sires used and first lactation females recorded per year. The number of nucleus daughters tested per sire, and of females per MOET full sibship, that maximize the predicted response to selection per year, were determined. Annual genetic gains and inbreeding rates were interpolated to the same planning horizon (20 years) to compare the optimized schemes for a wide range of situations. The predicted maximum genetic gain per year is higher for adult MOET than for juvenile MOET (due to the proportional extra time to collect the embryos needed) and for nucleus progeny testing. Average annual inbreeding rates are much higher for MOET schemes than for nucleus progeny testing. The advantages of adult and juvenile over nucleus progeny testing are little affected by planning horizon, but are higher with more females recorded per year, higher heritability, and higher reproductive and MOET success rates. Comparison of the schemes at the same level of inbreeding is fairer for fixed testing resources. At the same inbreeding level, the genetic advantage of adult MOET was generally maintained, but juvenile MOET then lost its advantage over progeny testing in these closed populations. ZUSAMMENFASSUNG: Optimierte Prüfpl?ne für Nukleusnachkommen, adulte MOET Geschwister oder juvenile MOET Pedigrees in geschlossenen Milchviehpopulationen Selektionserfolge werden für Nukleusnachkommenprüfung, adulte multiple Ovulation (MOET) und Embryotransfer, Geschwisterprüfung und juvenile MOET Pedigreeprüfung geschlossener Populationen gesch?tzt. Deterministische Modelle werden modifiziert zur Berücksichtigung gesch?tzter genetischer Fortschritte für die Wirkungen von Populationsgr??e, Struktur, Selektionsungleichgewicht, Stichprobenungenauigkeit und Inzuchtdepression. Die Zuchtpl?ne werden für verschiedene Zahlen von Stieren und Erstlaktationskühe pro Jahr optimiert. Die Zahl der geprüften Nukleust?chter je Stier und Kühe je MOETVollgeschwistergruppe, die den gesch?tzten Erfolg maximieren, werden bestimmt. Um die optimierten Pl?ne über einen weiten Bereich zu vergleichen, werden j?hrlicher Zuchtfortschritt und Inzuchtzuwachs für den gleichen Planungshorizont von 20 Jahren interpoliert. Der gesch?tzte maximale Zuchtfortschritt pro Jahr ist für adultes MOET h?her als bei juvenilem (wegen zus?tzlicher Zeit zur Embryonengewinnung) und bei Nukleusnachkommenschaftsprüfung. Durchschnittliche j?hrliche Inzuchtraten sind viel h?her für MOET Pl?ne als für das Nachkommenschaftsprüfsystem. Die Vorteile des adulten und juvenilen MOET über Nukleusnachkommenprüfung werden durch den Planungshorizont nur geringfügig tangiert, werden aber h?her, wenn mehr weibliche Tiere je Jahr geprüft werden bei h?herer Heritabilit?t, h?herer Reproduktions- und Erfolgsrate. Der Vergleich der Pl?ne beim gleichen Inzuchtniveau ist für gegebene Testresourcen angemessener.     

Optimization of selection and mating schemes in closed broiler lines

Minimum coancestry mating (MC) is a simple mating system to reduce inbreeding in populations, in which matings are allocated so as to minimize the average inbreeding coefficient of progeny. This system was compared with random mating (RM) in simulated broiler lines. The population structure and genetic parameters were determined on the basis of an existing broiler line. Comparison of mating systems was made under two selection methods. The first method (DIS) was based on selection index for achieving desired genetic gains. In the second method (LPS), a combination of the family index and linear programming technique was applied to obtain the desired genetic gains. The selected traits were body weight at 6 weeks of both sexes and age at sexual maturity of hen. Four schemes by all the possible combinations of selection and mating methods (DIS + RM, DIS + MC, LPS + RM and LPS + MC) were compared in terms of genetic gains and inbreeding during 15 generations of selection and mating. The results obtained are summarized as follows: (i) the four schemes produced similar genetic gains averaged over replicates; (ii) the variations of genetic gains under LPS + RM and LPS + MC schemes were much smaller than under DIS + RM and DIS + MC schemes; (iii) irrespective of the selection methods, MC reduced the average inbreeding coefficients to about 80% of RM and; (iv) the inbreeding coefficients of individuals in the schemes with RM were distributed in a wide range, while the inbreeding coefficients in the schemes with MC showed a high uniformity. From these results, the LPS + MC scheme was recommended as a selection and mating strategy in closed broiler lines.     

Effect of sire mating patterns on future genetic merit and inbreeding in a closed beef cattle population

Summary Alternative breeding strategies were simulated based on the population structure of the Tajima strain of Japanese Black cattle. An analysis of the population structure revealed that some sires up to 20 years of age have been used in Tajima. In addition, 95% of newborn calves were the progeny of only 20 sires, and their mating frequencies were significantly skewed. The current average inbreeding coefficient and founder genome equivalents of the strain were estimated to be 0.199 and 2.25, respectively. Average inbreeding coefficient is expected to reach 0.394 within 27 years. Thus, different breeding strategies were assessed for their effect on the level of inbreeding and average genetic merit. We compared strategies that (1) halve the sire service period, (2) double the number of mating sires and (3) lower the skewed sire mating frequency and optimize the frequency for weighted genetic merit and diversity. Reducing the service period yielded a 7.0–12.0% reduction in the rate of inbreeding while maintaining almost the same genetic gain. Increasing the number of sires resulted in a 19.3–21.3% reduction in inbreeding with a corresponding 1.6–8.4% reduction in gain. The rates of inbreeding from the optimized strategies decreased as the weight on genetic diversity increased. However, a strategy that emphasized only genetic gain yielded lower gain than other strategies because the strategy allowed only one sire to mate, resulting in reduced genetic variance and low accuracy of genetic evaluation. In contrast, a strategy with no emphasis on genetic gain when determining mating frequency resulted in reductions of 16.0% and 63.2% in genetic gain and inbreeding, respectively. The strategies examined here are easily applicable and can be expected to reduce immediate loss of genetic diversity.     

Bull Selection in MOET Nucleus Breeding Schemes with Limited Testing Capacity

Centralized multiple ovulation and embryo transfer (MOET) nucleus breeding schemes with limited testing capacity were compared with a conventional artificial insemination (AI) scheme using a simulation. The donor cows were selected after their first lactation. In the hybrid MOET schemes, bulls were progeny tested in the AI population. In comparison, two other schemes used nucleus-born adult bulls only. The best hybrid scheme gave 77% or 40% better genetic response in milk protein yield than that estimated in the national AI scheme when the assumed genetic progress in the AI scheme was low or high, respectively. The best scheme had acceptable coefficients of variation of genetic response, although the rate of inbreeding was 2.5 times higher than in the national AI scheme. The schemes using adult bulls had lower responses and higher rates of inbreeding than the hybrid schemes. The outstanding performance of the hybrid schemes was due to more successful cow selection path than in a conventional AI scheme. A high accuracy of selection of bulls was also important.     

公母畜间有不同的年龄组数目条件下控制近交最大化选择反应

一种扩展的动态选择规则能够在公母畜间有不同的年龄组数目的世代重叠群体内约束年近交速率为一个预定义值，逐年最大化遗传反应。该规则考虑在世代重叠群体中按性别一年龄分组，通过限制父母亲群体性别一年龄组的平均加性遗传相关的增加，从而限制新生后代平均近交系数的增加。动态选择程序通过输入候选个体的BLUP估计育种值、所有个体的加性遗传相关矩阵和所有性别一年龄组的长期遗传贡献，给出最适宜的选留个体数及其每个选留个体最适宜的后代数。猪核心群随机模拟结果显示该动态选择规则能够获得预定义的近交速率。在相同的近交速率条件下，动态选择比截断选择获得高达10％的更多年遗传进展。     

Optimum contribution selection using traditional best linear unbiased prediction and genomic breeding values in aquaculture breeding schemes

The aim of this study was to compare genetic gain for a traditional aquaculture sib breeding scheme with breeding values based on phenotypic data (TBLUP) with a breeding scheme with genome-wide (GW) breeding values. Both breeding schemes were closed nuclei with discrete generations modeled by stochastic simulation. Optimum contribution selection was applied to restrict pedigree-based inbreeding to either 0.5 or 1% per generation. There were 1,000 selection candidates and a sib test group of either 4,000 or 8,000 fish. The number of selected dams and sires to create full sib families in each generation was determined from the optimum contribution selection method. True breeding values for a trait were simulated by summing the number of each QTL allele and the true effect of each of the 1,000 simulated QTL. Breeding values in TBLUP were predicted from phenotypic and pedigree information, whereas genomic breeding values were computed from genetic markers whose effects were estimated using a genomic BLUP model. In generation 5, genetic gain was 70 and 74% greater for the GW scheme than for the TBLUP scheme for inbreeding rates of 0.5 and 1%. The reduction in genetic variance was, however, greater for the GW scheme than for the TBLUP scheme due to fixation of some QTL. As expected, accuracy of selection increased with increasing heritability (e.g., from 0.77 with a heritability of 0.2 to 0.87 with a heritability of 0.6 for GW, and from 0.53 and 0.58 for TBLUP in generation 5 with sib information only). When the trait was measured on the selection candidate compared with only on sibs and the heritability was 0.4, accuracy increased from 0.55 to 0.69 for TBLUP and from 0.83 to 0.86 for GW. The number of selected sires to get the desired rate of inbreeding was in general less in GW than in TBLUP and was 33 for GW and 83 for TBLUP (rate of inbreeding 1% and heritability 0.4). With truncation selection, genetic gain for the scheme with GW breeding values was nearly twice as large as a scheme with traditional BLUP breeding values. The results indicate that the benefits of applying GW breeding values compared with TBLUP are reduced when contributions are optimized. In conclusion, genetic gain in aquaculture breeding schemes with optimized contributions can increase by as much as 81% by applying genome-wide breeding values compared with traditional BLUP breeding values.     

基于基因组和系谱信息的不同选配方案效果模拟研究

基因组选配（genomic mating,GM）是利用基因组信息进行优化的选种选配,可以有效控制群体近交水平的同时实现最大化的遗传进展。但基因组选配是对群体中所有个体进行选配,这与实际的育种工作有点相悖。本研究模拟了遗传力为0.5的9 000头个体的基础群数据,每个世代根据GEBV选择30头公畜、900头母畜作为种用个体,而后使用基因组选配、同质选配、异质选配、随机交配4种不同的选配方案。其中基因组选配中分别选取遗传进展最大的解、家系间方差最大的解、近交最小的解所对应的交配方案进行选育。每种方案选育5个世代,比较其后代群体的平均GEBV、每世代的遗传进展、近交系数、遗传方差,并重复5次取平均值。结果表明,3种基因组选配方案的ΔG均显著高于随机交配和异质选配（P<0.01）,而且,选取遗传进展最大的基因组选配方案的ΔG比同质选配还高出4.3%。3种基因组选配的方案的ΔF比同质选配低22.2%~94.1%,而且选取近交最小的基因组选配方案ΔF比异质选配低11.8%。同质选配的遗传方差迅速降低,在第5世代显著低于除基因组选配中选择遗传进展最大的方案以外的所有方案（P<0.05）,3种基因组选配方案的遗传方差比同质选配高10.8%~32.2%。这表明基因组选配不仅可以获得比同质选配更高的遗传进展,同时有效的降低了近交水平,并且减缓了遗传方差降低速度,保证了一定的遗传变异。基因组选配作为一种有效的可持续育种方法,在畜禽育种中开展十分有必要。     

近交与贴现对优化群体规模的影响

小群体的闭锁选育不可避免产生近交及遗传方差下降，导致近期与远期选择效果的矛盾。本文通过考察猪核心群育种方案中群体规模及公母比例对近交增量（％）及累积育种产出（元）的作用，分析遗传方差下降以及育种产出的贴现等因素对选择方案评估效果的影响。群体有效规模主要受每世代选择公猪头数的影响，为了控制群体近交增量必须维持一定的公猪头数。在所模拟的１６种方案中，１５代的贴现累积选择进展以每代选择８头公猪为最高；而母猪规模越大，累积选择进展越高。不考虑近交引起遗传方差的下降，或不进行选择进展的贴现，都造成过高估计选择方案的效果，且导致选择不适当的方案；对各世代选择进展进行贴现时，需要考虑较大的世代数，否则也会影响各选择方案的比较结果。     

Stochastic simulation of Manchega sheep breed selection scheme. Impact of artificial insemination, progeny testing system and nucleus size on genetic progress and inbreeding

Manchega is a local Spanish sheep breed located in the region of Castilla la Mancha, Actually there are 0.8 million of milked ewes. The selection scheme of Manchega breed (ESROM) started in 1988, involving a selection nucleus composed by 103,887 ewes distributed in 106 flocks. Results obtained from the ESROM has been moderate in comparison with other similar European schemes. By this and other reasons, to develop a specific tool to study the ESROM system seems to be necessary.

The objectives of this work were to develop a genetic simulation model based on the ESROM real system and to study the effects on genetic progress and inbreeding level achieved from different rates of AI used, the progeny test system and the selection nucleus size.

An additive infinitesimal model was assumed for the trait 120 days Total Milk Yield (TMY). Five alternatives selection criteria (two per each group of animals to be selected), differentiated on their selection intensities, were associated to the selection of lambs for future artificial insemination rams, natural mating rams and ewes. All selection decisions were based on periodical genetic evaluations (BLUP), using an animal model with repeated measures. 60 specific cases were studied, each one with 20 replicates.

An average true genetic progress per year ranging from 1.04% to 2.10% in AI rams and 0.59% to 2.11% in ewes were observed. Results of phenotypic progress varied from 0.44% to 1.83% per year. True inbreeding levels of ewes at year 17 were between 0.218% and 1.879%.

The model used had the expected behavior. In general, the studied selection scheme had its better results (maximum genetic progress), when AI rate was equal or greater than 50%, a greater number of new rams were tested per year (75 and 44) and a selection nucleus size equal or greater than 9000 ewes (30 flocks). Selection intensity of natural mating rams had a great impact on the genetic progress, especially when the use of AI was low. The greater the nucleus size, the higher the genetic progress, but an operative scheme from around 9000 initial ewes could be established.

Results observed demonstrate the existence of some critical areas, which could be verified on the real system in order to improve their effectiveness. In this framework, the ESROM could develop two complementary strategies: to improve the selection system of Natural Mating Rams (selecting only sons of AI rams) and/or to increase the levels of AI until 50%.     

A mating system to reduce inbreeding in selection programmes: Theoretical basis and modification of compensatory mating

Increased rate of inbreeding in selection programmes may have an important effect on mid- and long-term selection response and reproductive performance through reduction in genetic variance and inbreeding depression. Selection on an inherited trait inflates the rate of inbreeding and reduces the effective population size (R obertson 1961; S antiago and C aballero 1995). This can be particularly important in selection based on index with information from relatives (L ush 1947) or best liner unbiased prediction (BLUP) with an animal model (H enderson 1984). In recent years, various methods have been proposed to reduce the rates of inbreeding in selection programmes while keeping genetic gains at the same level. These methods assume various selection and mating strategies. G rundy et al. (1994) showed that the use of biased heritability estimates for BLUP evaluation is one of the simplest and most efficient methods. A direct reduction in the weight on family mean in index selection (T oro and P erez -E nciso 1990), selection for weighted ancestral Mendelian sampling estimates (W oolliams and T hompson 1994; G rundy et al. 1998) and limited use of selected parents (T oro and N ieto 1984; W ei 1995) have also been shown to be efficient methods. Other methods include nonrandom matings of selected parents, such as factorial mating designs (W oolliams 1989), minimum coancestry mating (T oro et al. 1988) and compensatory mating (S antiago and C aballero 1995). Simultaneous optimization of the selection of candidates and their mating allocations has been also considered through mate selection with linear programming techniques (T oro and P erez -E nciso 1990). Among these methods, compensatory mating is a very simple and efficient method (G rundy et al. 1994; S antiago and C aballero 1995; C aballero et al. 1996). This mating system was derived from the theoretical consideration on effective population size under selection (S antiago and C aballero 1995). Although S antiago and C aballero (1995) considered that implementation of this mating could counteract the cumulative effect of selection on the effective population size, the theoretical basis has been little studied. In this paper, the author gives the theoretical basis of compensatory mating. A modification to enhance the effect of compensatory mating is also proposed and the efficiency is examined by stochastic simulation.     

Predicting rates of inbreeding for livestock improvement schemes

This article presents a deterministic method to predict rates of inbreeding (deltaF) for typical livestock improvement schemes. The method is based on a recently developed general theory to predict rates of inbreeding, which uses the concept of long-term genetic contributions. A typical livestock breeding population was modeled, with overlapping generations, BLUP selection, and progeny testing of male selection candidates. Two types of selection were practiced: animals were either selected by truncation on estimated breeding values (EBV) across age classes, or the number of parents selected from each age class was set to a fixed value and truncation selection was practiced within age classes. Bulmer's equilibrium genetic parameters were obtained by iterating on a pseudo-BLUP selection index and deltaF was predicted for the equilibrium situation. Predictions were substantially more accurate than predictions from other available methods, which ignore the effect of selection on deltaF. Predictions were accurate for schemes with up to 20 sires. Predicted deltaF was somewhat too low for schemes with more than 20 sires, which was due to the use of simple linear models to predict genetic contributions. The present method provides a computationally feasible (i.e., deterministic) tool to consider both the rate of inbreeding and the rate of genetic gain when optimizing livestock improvement schemes.     

Multiple ovulation and embryo manipulation in the improvement of beef cattle: relative theoretical rates of genetic change

Theoretical rates of annual genetic responses to selection in beef cattle were compared for conventional and multiple ovulation and embryo transfer (MOET) breeding schemes. Several combinations of replacement policy, mating ratio and type of selection were considered for both schemes with low, medium and high heritabilities. For MOET, four rates of embryo transfers per donor were used to represent low to moderate MOET levels. The results indicated that annual genetic responses to selection could be up to 1.3, 1.6 and 1.8 times as great for MOET compared with conventional breeding for traits of low, medium and high heritability, respectively; however, the annual inbreeding rates also were high for the MOET schemes considered. Embryo splitting, or cloning, was shown to increase accuracy of selection by 8 to 35% through the production of identical genotypes. The use of MOET in conjunction with embryo splitting in elite nucleus units could substantially increase genetic improvement for traits with low, medium and high heritabilities in beef cattle populations.     

The joint regulation of genetic gain and inbreeding under mate selection

SUMMARY: Stochastic simulation was used to evaluate a range of selection strategies with respect to both additive genetic response and inbreeding. Strategies involving selection on BLUP ebvs or individual phenotype, followed by random mating, were compared with mate selection strategies which used portfolio analysis to give joint consideration to genetic merit and inbreeding. An adapted Mean Of Total Absolute Deviations (MOTAD) method was used in a mate selection model to define optimal matings with regard to aggregate genetic merit and inbreeding for a base population h(2) of 0.2. Compared with random mating following selection on BLUP ebvs, inbreeding levels after 10 years of selection were able to be reduced under BLUP plus mate selection from ～.23 to as little as .11. Additive genetic gain was either little compromised or increased. The results suggest that information linking expected levels of genetic merit and inbreeding can be used to find the preferred selection strategy. ZUSAMMENFASSUNG: Gemeinsame Kontrolle von Zuchtfortschritt und Inzucht bei Partnerselektion Es wurde stochastische Simulation zur Auswertung einer Reihe von Selektionsstrategien hinsichtlich Zuchtwertzuwachs und Inzucht verwendet. Strategien mit Selektion auf der Basis von BLUP ebvs oder individuellem Ph?notyp mit nachfolgender Zufallspaarung wurden mit Partnerselektionsstrategien verglichen, die Portfolioanalyse zur gemeinsamen Beachtung von Zuchtwert und Inzucht verwendeten. Eine Methode adaptierter MITTELWERTE TOTALER ABSOLUTER ABWEICHUNGEN (MOTAD) Methode wurde beim Partnerselektionsmodell zur Definition optimaler Paarungen in Hinblick auf Gesamtzuchtwert und Inzucht bei einer Populationsheritabilit?t von 0,2 verwendet. Verglichen mit Zufallspaarung nach Selektion auf BLUP ebvs waren die Inzuchtgrade nach 10 Selektionsjahren von 0,23 auf 0,11 reduziert und additiver Zuchtfortschritt war dabei wenig beeintr?chtigt oder nahm sogar zu. Die Ergebnisse weisen darauf hin, da? Information, die Zuchtwert und Inzucht verbindet, zur Identifikation erwünschter Selektionsstrategien führen kann.     

Approaches to the management of inbreeding and relationship in the German Holstein dairy cattle population

The aim of this study was to estimate the current level of inbreeding in the German cow population and for bull dams born in Germany, to find out sires most related to different subsets of their breed and to demonstrate the negative effect of homozygosity in the case of complex vertebral malformation (CVM). Further on, the application of optimum genetic contribution (OGC) theory for the selection of bull dams and bull sires in different breeding scenarios was investigated. Levels of inbreeding for the cow population were in a low range from 0.97% to 1.70% evaluating birth years from 1996 to 1999 in a total dataset of 244,427 registered Holstein cows. The inbreeding coefficient of 8030 bull dams was much higher, i.e. 3.71%, for the birth year 1999. Increases in inbreeding of 0.19% per year indicated an effective population size of only 52 animals. Individual sires like R.O.R.A. Elevation and Hannoverhill Starbuck were highly related to potential bull dams with coefficients of relationship of 13.4% and 12.9%, respectively, whereas P.F. Arlinda Chief (16.3%) and Carlin-M Ivanhoe Bell (16.1%) were highest related to the best available AI sires. Coefficients of relationship were calculated by classes of estimated breeding values (EBV) for production traits showing highest values above 7% in the two highest EBV-classes. The optimum genetic contribution theory using official EBVs and approximative, for zero inbreeding corrected EBVs, was applied for elite matings in a breeding program embracing 30 young bulls per year to find the optimal allocations of bull sires and bull dams. Compared with the actual breeding program applied in practice, OGC-theory has the potential to increase genetic gain under the same constraint for the increase of average relationship by 13.1%. A more relaxed constraint on increase in inbreeding allowed even higher expected genetic gain whereas a more severe constraint resulted in more equal contributions of selected bull sires. Contributions from 21 selected bull sires and 30 selected bull dams for a scenario at 5% constrained relationship were used to develop a specific mating plan to minimise inbreeding in the short term in the following generation applying a simulated annealing algorithm. The expected coefficient of inbreeding of progeny was 66.3% less then the one resulting from random mating. Mating programs can address inbreeding concerns on the farm, at least in the short term, but long-term control of inbreeding in a dairy population requires consideration of relationships between young bulls entering AI progeny test programs. Significantly better EBVs of CVM-free bulls compared with CVM-carriers for the paternal fertility justify the application of OGC for elite matings.     

Optimal village breeding schemes under smallholder sheep farming systems

Despite challenges in the implementation of livestock genetic improvement programs in developing regions, including centralized nucleus breeding schemes, these programs can contribute to the improvement of the livelihood of smallholder farmers. In this paper, we present a community- or village-based breeding scheme in which breeding activities are carried out by communities of smallholder farmers. We evaluated genetic responses and the rate of inbreeding from alternative village sheep breeding schemes that were based on a survey of existing flock structure and breeding management in a sheep-barley system in Ethiopia. This survey showed that individual flock sizes were small, and that the majority of farmers practiced mixed grazing and uncontrolled mating of their flocks in communal grazing lands within villages. Here we evaluated within-village schemes (selection across flocks within a village) and across-village schemes (selection across villages) at different intensities of ram selection (i.e. proportions of rams selected, P). Our results showed that under within-village schemes, intensity of selection could not be increased (i.e. P could not be decreased below 0.149) when the rate of inbreeding was constrained to an acceptable level of 0.01, resulting in low genetic gain. The most optimal scheme was found to be across-village selection with at least three villages cooperating and P = 0.05. Our results also indicated that genetic gain from village breeding schemes with mass selection and BLUP selection is comparable. Village breeding schemes can make a significant contribution to the genetic improvement of livestock in Ethiopia and other developing countries.     

Genomic selection for maternal traits in pigs

The aim of this study was to compare alternative designs for implementation of genomic selection to improve maternal traits in pigs, with a conventional breeding scheme and a progeny testing scheme. The comparison was done through stochastic simulation of a pig population. It was assumed that selection was performed based on a trait that could be measured on females after the first litter, with a heritability of 0.1. Genomic selection increased genetic gain and reduced the rate of inbreeding, compared with conventional selection without progeny testing. Progeny testing could also increase genetic gain and decrease the rate of inbreeding, but because of the increased generation interval, the increase in annual genetic gain was only 7%. When genomic selection was applied, genetic gain was increased by 23 to 91%, depending on which and how many animals were genotyped. Genotyping dams in addition to the male selection candidates gave increased accuracy of the genomic breeding values, increased genetic gain, and decreased rate of inbreeding. To genotype 2 or 3 males from each litter, in order to perform within-litter selection, increased genetic gain 8 to 12%, compared with schemes with the same number of genotyped females but only 1 male candidate per litter. Comparing schemes with the same total number of genotyped animals revealed that genotyping more females caused a greater increase in genetic gain than genotyping more males because greater accuracy of selection was more advantageous than increasing the number of male selection candidates. When more than 1 male per litter was genotyped, and thereby included as selection candidates, rate of inbreeding increased because of coselection of full sibs. The conclusion is that genomic selection can increase genetic gain for traits that are measured on females, which includes several traits with economic importance in maternal pig breeds. Genotyping females is essential to obtain a high accuracy of selection.     

Effects of genotype x environment interaction on genetic gain in breeding programs

Genotype x environment interaction (G x E) is increasingly important, because breeding programs tend to be more internationally oriented. The aim of this theoretical study was to investigate the effects of G x E on genetic gain in sib-testing and progeny-testing schemes. Loss of genetic gain due to G x E was predicted for different values of heritability, number of progeny per dam, number of progeny per sire, proportion of selected sires, and population size in the selection environment. Two environments were considered: a selection environment (SLE) and a production environment (PDE). The breeding goal was only for performance in PDE. A pseudo-BLUP selection index was used to predict genetic gain. Recording of half-sibs or progeny in PDE limited the loss in genetic gain in PDE due to G x E between SLE and PDE. Progeny-testing schemes had less loss in genetic gain than sib-testing schemes. Higher heritability increased the loss in genetic gain, whereas increasing the number of progeny per sire in PDE decreased the loss in genetic gain. The number of progeny per sire required to minimize loss in genetic gain due to G x E was greater for sib-testing schemes than for progeny-testing schemes. More progeny per dam slightly increased the loss in genetic gain. Genetic gains for sex-limited and carcass traits were less affected by G x E than traits measured on both sexes. Loss in genetic gain was due to decreased accuracy of selection in most situations, but it was due to decreased selection intensity in situations with small population size and a low proportion of selected sires. It was concluded that recording performance of relatives in PDE minimizes loss in genetic gain due to G x E, and that progeny-testing schemes rather than sib-testing schemes are preferable in situations with low to moderate heritability (h(2) 相似文献   

Economic efficiency of Japanese Black cattle selection schemes utilizing crossbreeding with the Holstein breed

The economic efficiency of Japanese Black (JB) cattle selection schemes utilizing crossbreeding with the Holstein (H) breed was evaluated in the context of maximizing profitability. Selection schemes were defined that differed in the records available for use as selection criteria. The selection schemes were assessed based on profitability per cow in the JB cattle population. Within each selection scheme, two terminal crossbreeding systems were considered: two‐way crossbreeding without backcrossing (F₁ system) and two‐way crossbreeding with backcrossing (F₁ cross system). The impact on profitability of varying number of sires selected per year and the proportion of H cows that were inseminated by JB semen and of F₁ females that are retained for replacement was examined for all selection schemes. Utilizing crossbreeding with the H breed was less profitable than purebreeding of the JB. Profitability was higher in the F₁ system than in the F₁ cross system in all selection schemes. Profitability was influenced more by changes in the number of sires selected per year than by the proportion H cows that were inseminated by JB semen and of F₁ females that were retained for replacement. Implications of these results for the JB breeding program are discussed.