EPD估计的原理与应用

EPD是在BLUP理论的基础上对种用动物遗传值估计的一种参数。EPD值是估计育种值的一半，它是一个容易理解和应用的种畜遗传传递力的值，能很直观地反映种畜价值在其后代中的体现。EPD主要是用在同一品种中2个不同个体间直接遗传效应的比较，从而预测在同一平均遗传值水平上种用动物未来子女的性能差异。EPD适用于动物的出生、发育、母性性状、屠宰性状以及其它特征性状的估计。EPD广泛应用于肉用种公牛价值的评定。对肉牛重要经济性状EPD估计后，以出版物和（或）计算机网络的方式发布，肉牛生产者根据自己的不同需要选用种牛或精液。作者对EPD的估计原理与应用作较为详细的论述。     

肉用公牛选择的关键信息

自60年代起．肉牛生产者开始对肉牛性状如易产性、生长速度、饲料转化率、母性抚育能力和胭体品iff＄行度量和选择。最初是采用个体表型值作为选择指标．如个体的周岁体重这一表型度量值是用于选择肉牛生长速度的指标,当被选择或被比较的个体所处的环境和饲养管理条件相同B4A种选择是有效的。否则就不够准确和公正。为了消除不同环境差异的影响。采取了后裔测定的办法来评价一头公牛的真正的遗传品质。早期的公牛评价结果使用估计育种值（EBV）、今天采取对品种内所有有记录的种畜的后裔资料进行统计分析和遗传评价的预期后裔差异（EPD…     

长白母猪繁殖性状的相关分析

畜牧业生产实践中,种畜种用价值的评定是一个很重要的环节。现代选择理论的发展已为种畜提供了多种评定方案,如育种值估计、合并选择指数、综合选择指数以及最佳线性无偏估计（BLUP）等。     

从应用BLUP到种猪发展

多性状动物模型BLUP(Best Linear UnbiasedPrediction)法是当今世界上先进的育种值估计方法,能消除各种环境因素的影响,利用各种亲属资料,考虑选择近交及性状间遗传相关等因素,准确地同时估计出种畜各性状育种值以及综合育种值,并能比较场内,场间,地区间甚至国家间种畜优劣,可加速优良种畜的推广利用,提高种畜质量。     

复合育种值电算估测

一、前言种畜价值的评定不能停留在表型值,而要通过表型值去估计育种值,因此学术界十分重视估计方法的研究,例如系谱鉴定、个体鉴定、同胞鉴定和后裔鉴定等,但是这些都测重于按单项资料估计,对于如何利用多项资料的信息,进行最优复合估计的问题,以往研究和应用甚少。     

应用优秀种公牛改良中国荷斯坦牛群的效果分析

分析了应用优秀种公牛改良黑龙江省中国荷斯坦奶牛群主要经济性状的效果。结果表明：该地区多年来推广优良种公牛提高了生产水平,改善了奶牛群体型和繁殖力,同时证明了合理利用优秀种公牛仍是目前提高遗传品质,加速牛群育种进展,创造高产长寿奶牛群的有效途径。在种畜遗传评定中分析比较了不同模型育种植的估计结果,论证了采用动物模型进行种畜评定的准确性要高于公畜模型。     

基于EXCEL种畜BLUP育种值的程序设计

采用Excel自带的VBA语言编程,开发出一个依赖Excel运行的应用宏,实现了种畜最佳线性无偏预测法（BLUP）育种值的自动分析功能,增强了种畜育种值估计的准确性,提高了种畜选种的效果。     

BLUP中分子血缘相关矩阵A逆阵的直接计算法

自上个世纪８０年代以来，随着计算技术的发展，BLUP法在动物生产特别是奶牛和肉牛生产上得到广泛应用，使动物的改良效益大幅度提高。畜牧业发达国家，商用种畜的价值评定主要依据BLUP结论。我们知道，BLUP是建立在混合模型基础上的动物育种值的线性评定方法。为了计算模型中动物个体间遗传效应协方差，需要计算分子血缘相关矩阵的逆矩阵。从逆矩阵的常规运算思路出发，是先建立血缘相关矩阵再求它的逆矩阵。然而，当动物个体数量很大时，这种由矩阵而逆矩阵的计算，就目前的计算技术是不可能完成的。BLUP的创始人Henderson（１９７…     

内蒙古优质肉牛生产基地建设的探讨（上）

提出在“十五”期间，内蒙古自治区肉牛业的主攻方向应该是以种畜产业化为突破口，加快肉牛“种子工程”建设步伐，以市场为导，以科技为先导，以资源为依托，以肉牛业发展为主题，以调整肉牛产业结构为主线，以发展生产为重点，以促进农村牧区经济发展、社会繁荣和农牧民增收为目标，实行重点突破、全面推进，转变肉牛业增长方式。     

猪的育种值估计

估计育种值是种猪选育的主要依据，而育种值估计的准确性直接影响猪群的遗传进展。随着育种理论和实践的不断发展．育种值的估计方法也不断的发展和更新。近年来由于数理统计（尤其是线性模型理论）、计算机科学、计算数学等学科领域的迅速发展以及生物技术在动物育种中的应用，动物育种值估计的方法发生了很大的变化。在未来的猪育种工作中，依靠经典理论和先进的科学技术提高育种值估计的准确度，依然是今后育种工作的重点。     

Genetic evaluation of the probability of pregnancy at 14 months for Nellore heifers

To estimate the heritability for the probability that yearling heifers would become pregnant, we analyzed the records of 11,487 Nellore animals that participated in breeding seasons at three farms in the Brazilian states of S?o Paulo and Mato Grosso do Sul. All heifers were exposed to a bull at the age of about 14 mo. The probability of pregnancy was analyzed as a categorical trait, with a value of 1 (success) assigned to heifers that were diagnosed pregnant by rectal palpation about 60 d after the end of the breeding season of 90 d and a value of 0 (failure) assigned to those that were not pregnant at that time. The estimate of heritability, obtained by Method R, was 0.57 with standard error of 0.01. The EPD was predicted using a maximum a posteriori threshold method and was expressed as deviations from 50% probability. The range in EPD was -24.50 to 24.55%, with a mean of 0.78% and a SD of 7.46%. We conclude that EPD for probability of pregnancy can be used to select heifers with a higher probability of being fertile. However, it is mainly recommended for the selection of bulls for the production of precocious daughters because the accuracy of prediction is higher for bulls, depending on their number of daughters.     

DNA-based paternity analysis and genetic evaluation in a large, commercial cattle ranch setting

Deoxyribonucleic acid-based tests were used to assign paternity to 625 calves from a multiple-sire breeding pasture. There was a large variability in calf output and a large proportion of young bulls that did not sire any offspring. Five of 27 herd sires produced over 50% of the calves, whereas 10 sires produced no progeny and 9 of these were yearling bulls. A comparison was made between the paternity results obtained when using a DNA marker panel with a high (0.999), cumulative parentage exclusion probability (P(E)) and those obtained when using a marker panel with a lower P(E) (0.956). A large percentage (67%) of the calves had multiple qualifying sires when using the lower resolution panel. Assignment of the most probable sire using a likelihood-based method based on genotypic information resolved this problem in approximately 80% of the cases, resulting in 75% agreement between the 2 marker panels. The correlation between weaning weight, on-farm EPD based on pedigrees inferred from the 2 marker panels was 0.94 for the 24 bulls that sired progeny. Partial progeny assignments inferred from the lower resolution panel resulted in the generation of EPD for bulls that actually sired no progeny according to the high-P(E) panel, although the Beef Improvement Federation accuracies of EPD for these bulls were never greater than 0.14. Simulations were performed to model the effect of loci number, minor allele frequency, and the number of offspring per bull on the accuracy of genetic evaluations based on parentage determinations derived from SNP marker panels. The SNP marker panels of 36 and 40 loci produced EPD with accuracies nearly identical to those EPD resulting from use of the true pedigree. However, in field situations where factors including variable calf output per sire, large sire cohorts, relatedness among sires, low minor allele frequencies, and missing data can occur concurrently, the use of marker panels with a larger number of SNP loci will be required to obtain accurate on-farm EPD.     

Additive genetic relationships between heifer pregnancy and scrotal circumference in Nellore cattle

To estimate heritability (h2) for yearling heifer pregnancy and to estimate the genetic correlation between heifer pregnancy and scrotal circumference, 18,145 records of Nellore heifers exposed to breeding at an age of approximately 14 mo and 25,466 records of contemporary young bulls were analyzed. Heifer pregnancy was considered as a categorical trait, with the value 1 (success) assigned to heifers that were pregnant after rectal palpation approximately 60 d after the end of a 90-d breeding season and the value 0 (failure) otherwise. A single-trait animal model for heifer pregnancy and a two-trait animal model including heifer pregnancy and scrotal circumference were used. Contemporary groups were defined in two ways: including (CG2) or not including (CG1) weaning management of the heifer. Heritability estimates obtained by Method R in single-trait analyses were 0.68 +/- 0.09 and 0.61 +/- 0.10 using CG1 and CG2 definitions, respectively. Heritability estimates for two-trait analyses were 0.69 +/- 0.09 (CG1) and 0.63 +/- 0.08 (CG2) for heifer pregnancy and 0.57 +/- 0.03 (both CG) for scrotal circumference. The genetic correlation estimates between the two traits were 0.20 +/- 0.12 (CG1) and 0.20 +/- 0.13 (CG2). Based on the results of this study, EPD for heifer pregnancy can be used to select bulls for the production of precocious daughters and will be more effective than selecting on scrotal circumference EPD in Nellore cattle. However, scrotal circumference can be incorporated in a two-trait analysis to increase the accuracy of prediction for heifer pregnancy EPD for young bulls. Using contemporary group without heifer weaning management gave higher h2 and, for two-trait analysis, converged more quickly.     

Development of a simulation model to evaluate the effect of vaccination against Tritrichomonas foetus on reproductive efficiency in beef herds

OBJECTIVE: To develop a model to evaluate the effect of vaccination against Tritrichomonas foetus on reproductive efficiency in beef herds. SAMPLE POPULATION: A beef herd of 300 cows and 12 bulls (8 bulls < or = 3 years old and 4 bulls > 3 years old). PROCEDURE: The model was developed by use of data for various risk factors and vaccine efficacy. The reference herd was considered to be one in which T. foetus had been diagnosed and bulls were tested for T. foetus before the breeding season. Five thousand iterations were run for each of 13 simulations, with each simulation representing a separate combination of risk factors. RESULTS: In all simulations, vaccination resulted in significantly higher calving incidence than nonvaccination. Shared grazing was found to be the most significant risk factor for a decrease in calving incidence attributable to T. foetus infection, followed in importance by lack of testing before the breeding season and a higher proportion of old bulls. Combinations of risk factors contributed to a loss of income of up to 22%, some of which could be blunted by vaccination. CONCLUSIONS AND CLINICAL RELEVANCE: Highest calving incidence is achieved when all bulls are tested for T. foetus before the breeding season and all bulls with positive culture results are culled. Avoiding all risk factors is better than vaccinating, but when this is not feasible for a given herd, the results of this simulation indicate that proper vaccination can decrease economic losses attributable to abortions caused by T. foetus.     

Illustration of the maternal animal model used for genetic evaluation of beef cattle

National cattle evaluation programs for weaning weight in most beef breed associations involve implementation of the maternal animal model to predict direct and maternal EPD. With this model, direct breeding values are predicted for all animals with records or pedigree ties to animals with records, or both. Even though maternal genetic value is expressed only in animals that become dams, these effects are transmitted by all parents and inherited from parents by all animals, leading to maternal breeding values being predicted for all animals as well. A small example data set was simulated involving 12 parents, 8 nonparents, and 13 animals with weaning weight records. The pedigree was developed to include paternal and maternal half-sib families, full-sibs, and some inbreeding, similar to field populations of beef cattle. Assembly of the mixed model equations and solutions for the maternal animal model are illustrated explicitly to assist animal breeding students in their understanding of the properties of the maternal animal model and to explicitly implement the model. Model parameters and moments, fixed contemporary group solutions, adjustment of breeding values for merit of mates, interpretation of maternal permanent environmental effect solutions, and alternatives for the assembly of the equations are shown. This example should lead to increased student and producer understanding of genetic improvement programs for weaning weight in beef cattle.     

国内外肉牛遗传评估体系概况

种公牛的选育是肉牛育种工作的核心。传统选育肉用种公牛需要经过后裔测定进行选择,其优点是准确性高,但存在周期长、屠宰和肉质性状难以收集、成本高等问题,致其选择效率低。自2001年全基因组选择概念提出后,该技术迅速成为动植物育种领域研究的热点。利用全基因组选择进行肉用种公牛的选育,进行早期选择从而大幅度缩短世代间隔,可以提高繁殖性状等低遗传力性状的选择准确性,加快遗传进展,并大大降低育种成本。2014年,美国安格斯协会开始应用全基因组选择技术,其他欧美发达国家也陆续使用,肉牛育种进入基因组时代。中国自2017年开始使用全基因组选择技术选择青年肉用种公牛,并于2020年在全国范围内使用该技术进行基因组遗传评估。本文综述了国内外肉牛遗传评估现状,以期为我国肉牛育种工作提供参考和借鉴。     

Relationship between serving capacity of beef bulls as predicted by the yard test and their fertility during paddock mating

Six experiments were conducted to determine the relationship between the serving capacity of bulls as predicted by a 40-min yard test and their fertility during paddock mating, measured by the conception rate at first oestrus and the pregnancy rate at the end of 10 weeks of mating. Twenty bulls varying in serving capacity from 1 to 11 were mated to 40 heifers each. As serving capacity of the bulls increased from 1 to 7, conception rate increased from 18 to 70%. Average conception rates achieved by 4 bulls with low serving capacity (25.3%), 8 bulls with medium serving capacity (61.4%) and 7 bulls with high serving capacity (72.3%) were all significantly different from one another. Bulls of low serving capacity (1 or 2 services) impregnated a significantly lower proportion of their heifers (40.3%) than bulls with medium (91.2%) or high (95.3%) serving capacity. It was concluded that bulls of serving capacity 1 or 2 (in 40 min) should be considered unsound for breeding. An explanation for the results and their implication in beef production is discussed.     

Genetic Correlations Between Beef Traits Measured on Young Performance Test Bulls and Daughter Milk Yield

In a breeding programme where young potential breeding bulls are reared on performance test stations, selection based on own results can be carried out before test inseminations. Both beef and milk production traits are included in the total merit index used for selection, and estimates of genetic and phenotypic parameters of these traits are therefore of interest for an optimal construction of such indices. Data on first lactation milk records from the field and beef records of potential dairy breeding bulls from the Danish performance test stations were analysed in bivariate animal-sire models using the AI-REML algorithm. Genetic correlations of 0.16, 0.25 and 0.43 between feed intake capacity and protein yield were obtained for Red Danish (RD), Danish Black and White (DBW) and Danish Jersey (DJ), respectively. These correlations were significantly different from zero for the two populations (DBW and DJ). Genetic correlations around zero between feed efficiency and protein yield were obtained for all three populations. Genetic correlations of 0.44, 0.19 and 0.47 between average daily gain and protein yield were obtained for RD, DBW and DJ, respectively. The genetic correlations between protein yield and muscle area was close to zero for DBW, while it was -0.31 for RD. Selection index calculations indicate that indices composed of different beef performance traits can be used as early predictors for milk yield. Selection on such an index could increase the breeding value of the young bulls for milk production traits by 0.8-2.0% of the population mean.     

Observations on the Modified Serving Capacity Test for beef bulls

Over the period 1979-83, 466 beef bulls were examined physically and by Blockley's Modified Serving Capacity Test (M.S.C.T.). Seventy-eight bulls were diagnosed as unsound for breeding, of which 64 were detected by the M.S.C.T. Problems included locomotor abnormalities (6), low libido (14), penile deviation (33) and intromission failure (11). The animal welfare aspects of M.S.C.T. are discussed and its value in increasing herd fertility is illustrated with studies of two beef herds, which showed improvements of 4-5% in vetting in-calf rates after using the test.