首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
No national breeding programme for llamas is in place in Bolivia. Initiatives for genetic improvement are rarely found and are usually carried out by NGOs working in rural development or improvement of livestock production or research stations. Farmers in the Province of Ayopaya in the District of Cochabamba have formed a breeders’ organization with the aim of improving fibre production. In this study, a detailed outline of a breeding programme with a focus on organizational and technical details is described. Facing constraints like illiteracy of farmers, bad infrastructure and lack of finances, a simple breeding programme is set up. The breeding goal is a higher fleece weight while keeping the fleece quality at the current high level. Greasy fleece weight and fibre diameter are identified as main selection criteria. Mass selection of males is carried out. Selected males are either exchanged between farmers and used in the herds or are kept during the mating season in a central mating station owned by the breeders’ organization. Model calculations were carried out with the program zplan , which is based on a deterministic approach. zplan evaluates the genetic and economic efficiency of breeding strategies considering one cycle of selection. Scenarios with only intra-herd use, using only the central mating station or combinations of those were compared in terms of expected genetic gain and expected increase of inbreeding. Fastest genetic progress is achieved when the males are kept in a central mating station as the selection intensity is on a high level. Rates of inbreeding vary between 0.08 and 0.32% per generation.  相似文献   

2.
A study was conducted to characterize genetic diversity in the Alentejana breed of cattle based on its demographic trends and to investigate the major factors affecting genetic erosion in this breed. Herdbook information collected between 1940 and 2004, including pedigree records on 100,562 animals in 155 herds, was used to estimate demographic parameters. The mean generation intervals were 6.0 +/- 2.4 yr and 6.8 +/- 3.2 yr for sires and dams of calves, respectively. Average inbreeding increased steadily over the period analyzed, with an annual rate of inbreeding of 0.33 +/- 0.004% (P < 0.01) and an effective population size of 23.3. In the reference population (28,531 calves born between 2000 and 2003) the average inbreeding was 8.35 +/- 9.02% and nearly 80% of the calves were inbred, whereas the average relationship among all animals was 0.026 +/- 0.040. Nevertheless, the mean relationship was 0.328 +/- 0.264 and 0.022 +/- 0.026 for animals born in the same and in different herds, respectively. The computed genetic contributions to the reference population resulted in estimates for the effective number of founders, ancestors, founding herds, and herds supplying sires of 121.6, 55.0, 17.1, and 26.9, respectively, the 2 most influential herds and ancestors contributing 24.2 and 15.1%, respectively, of the current genetic pool. Of the 671 founding sires, only 24 Y-chromosomes are currently represented, but 1 sire alone contributes nearly 60% of this representation, such that the effective number of Y-chromosomes is only 2.73. The observed inbreeding per herd was, on average, 0.053 +/- 0.071 lower than expected from the relationship among the generation of parents of calves in the reference population, indicating that producers have followed breeding strategies that have kept inbreeding at lower levels than anticipated with random selection and mating. When compared with other cattle breeds, Alentejana has some of the highest levels of mean inbreeding and annual rate of inbreeding, and an effective population size that is nearly half of the minimum recommended for maintenance of genetic variability. These critical indicators demonstrate the need to adopt strategies aimed at minimizing inbreeding to avoid further losses of genetic diversity.  相似文献   

3.
Genetic parameters were estimated for purebred and crossbred progeny of Bavarian Piétrain sires on two test stations. The data set used contained 4276 purebred pigs and 13,980 crossbred pigs recorded between 2000 and 2004. In total 332 sires having purebred and crossbred progeny were available to estimate the genetic correlations between purebred and crossbred performances. Though the genetic correlations between purebred and crossbred pigs are fairly high (0.7–0.9), their performances have to be considered as genetically different traits, because variance components and heritabilities differ substantially. Therefore, purebred and crossbred breeding values of candidates are not identical, and thus result in different rankings. However, due to the high correlations purebred pigs provide a lot of information for estimating the crossbred breeding values of the real selection criterion. The Halothan locus, whose effects have been analyzed in detail, affects both purebred and crossbred parameters. To avoid detrimental effects on the efficiency of the breeding programme, the n-allele could be either eliminated or the genotypes of all test animals should be known. Differences in the variance components between the two test stations have been found and are problematic with respect to the breeding value estimation utilizing the pooled data set. Hence, it should be attempted to further improve the standardization of the performance test on both stations.  相似文献   

4.
This study compares two genetic management scenarios for species kept in herds, such as deer. The simulations were designed so that their results can be extended to a wide range of zoo populations. In the first scenario, the simulated populations of size 3 × 20, 6 × 40 or 20 × 60 (herds × animals in herd) were managed with a rotational mating (RM) scheme in which 10%, 20% or 50% of males were selected for breeding and moved between herds in a circular fashion. The second scenario was based on optimal contribution theory (OC). OC requires an accurate pedigree to calculate kinship; males were selected and assigned numbers of offspring to minimize kinship in the next generation. RM was efficient in restriction of inbreeding and produced results comparable with OC. However, RM can result in genetic adaptation of the population to the zoo environment, in particular when 20% or less males are selected for rotation and selection of animals is not random. Lowest rates of inbreeding were obtained by combining OC with rotation of males as in the RM scheme. RM is easy to implement in practice and does not require pedigree data. When full pedigree is available, OC management is preferable.  相似文献   

5.
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.  相似文献   

6.
Population structure of Reyna Creole cattle in Nicaragua   总被引：1，自引：1，他引：0  
Reyna Creole cattle originated from Bos taurus cattle brought to Latin America during the Spanish colonization in the fifteenth century and are the only remaining local breed in Nicaragua. However, the current genetic status of this breed is unknown. Therefore, the population structure of three recorded Reyna Creole herds in Nicaragua was studied to estimate their level of inbreeding, effective population size, and generation intervals. Data from 2,609 animals born between 1958 and 2007 were analyzed. A pedigree completeness index higher than 0.8 was required to obtain reliable estimates of the level of inbreeding, and this criterion was met for 367 animals (14%) in two herds. The average level of inbreeding was 13.0%, with values ranging from 0% to 43.8% for individual animals. One of the herds had an average inbreeding level of 21.6%, primarily due to long periods in which the same bulls were used for mating, leading to excessive frequencies of matings between closely related animals. The effective population size differed between years and ranged from 28 to 46 animals, showing that the Reyna Creole cattle breed is endangered, close to critical status. The average generation interval was 6.9 years with values as high as 19.1 years for some sires that were used for artificial insemination over a long period of time. Due to the high level of inbreeding and small population size, urgent actions are required for the development of a breeding program to protect the breed and support its sustainable utilization.  相似文献   

7.
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.  相似文献   

8.
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.  相似文献   

9.
Limiting the inbreeding rate (?F) while maximizing genetic gain for any trait of economic interest is especially important in small populations of local breeds, like the Menorca Horse. In this breed, dressage performance is important for the profitability of the breed and should be accounted in the selection criterion. The aim of this study was to assess if a breeding programme aiming at improved dressage performance is feasible in such a small breed. To perform the analysis, animals that were currently available for breeding (between 3 and 20 years) were used. Selection was based on the estimated breeding values for dressage obtained by BLUP. The pedigree and molecular coancestry between potential breeding horses was used (separately or in combination) to account for the restriction on ?F. Results show that it is possible to avoid large increases in inbreeding while obtaining acceptable levels of genetic gain (i.e. a ?F of 1% would imply a maximum loss in genetic gain of 2%). Thus, the Menorca Horse population is suitable for a management procedure which jointly optimizes the response to selection and the levels of variability and inbreeding (Optimal Contribution selection). Regarding the source of information used to calculate the relationships, molecular information would provide a greater range of solutions to increase genetic gain than using pedigree coancestry (gain was 1–4% higher for the same levels of restriction on the increase in inbreeding).  相似文献   

10.
Phenotypic and genetic trends were examined in 157,455 German shepherd dogs of the German population born between 1985 and 2003 which were Xrayed for canine hip dysplasia (CHD). A subset of 40,270 dogs born between 1998 and 2003 was examined for which information was available on age at examination and X-raying veterinary practitioner. Relative breeding values were predicted using best linear unbiased prediction methods (BLUP) and Gibbs Sampling. There was an almost linear and significant decline in both phenotypic and genetic trends for CHD scores (scale 1 to 5 for CHD free to severe CHD) over a period of 19 years, with b = -0.021 +/- 0.002, and b = -1.69 +/- 0.05, respectively. After introduction in 1999 of a selection scheme based on relative breeding values (RBVs, mean 100, standard deviation 20) of a linear animal model, phenotypic and genetic trends declined less than before 1999, with b = -0.019 +/- 0.011 and b = -1.43 +/- 0.29. Analysis of the effects of RBVs of parental combinations among sires and dams on the percentage of non-affected progeny showed that lower RBVs were associated with a higher percentage of non-affected progeny than were higher RBVs. In addition, it was also shown that selection procedures based on RBVs are more efficient than selection schemes based on phenotypic records of parents. When the maternal RBV was above 100, the proportion of non-affected progeny was between 10% and 20% lower than when the maternal RBV was below or equal to 100. There was a significant relationship between higher inbreeding coefficients and higher RBVs of the animal.  相似文献   

11.

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.  相似文献   

12.
In 1977 swine dysentery was made a notifiable disease in the German Democratic Republic, with the intention of eradicating it by the systematic treatment of clinically affected herds using intensive medication and hygiene control programmes. On individual farms the scheme appeared to be successful, but the national incidence of the disease did not decline, owing to the continuous presence of latently infected herds and the movement of carrier pigs to uninfected farms. In 1981 the scheme was re-appraised and a new scheme was introduced in one region where all the breeding herds were screened for the presence of Treponema hyodysenteriae; all positive herds were treated with either metronidazole or tylosin, and the movement of pigs into the region was controlled. This programme effectively eradicated the disease from the region and is being introduced to the rest of the country. Owing to concern about the safety of metronidazole and the development of resistance to tylosin, alternative antimicrobials were examined and tiamulin was selected to assess its suitability for inclusion in the programme. A 560 sow breeding herd and progeny were treated for five days with tiamulin at 10 mg/kg bodyweight. This was coupled with extensive cleaning, disinfection and rodent control programmes. The results of the trial showed that the clinical disease stopped in two days and that no further clinical signs were seen in the subsequent two-and-a-half years. Bacterial monitoring of faeces samples and colonic scrapings from dead pigs failed to identify viable T hyodysenteriae. There was a significant increase of 0.6 piglets weaned per litter and improvements in weaning weights and growth rates. It was concluded that tiamulin was suitable for inclusion in the swine dysentery eradication programme in the GDR.  相似文献   

13.
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。  相似文献   

14.

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.  相似文献   

15.
Deterministic simulation was used to evaluate 10 breeding schemes for genetic gain and profitability and in the context of maximizing returns from investment in Japanese Black cattle breeding. A breeding objective that integrated the cow-calf and feedlot segments was considered. Ten breeding schemes that differed in the records available for use as selection criteria were defined. The schemes ranged from one that used carcass traits currently available to Japanese Black cattle breeders (Scheme 1) to one that also included linear measurements and male and female reproduction traits (Scheme 10). The latter scheme represented the highest level of performance recording. In all breeding schemes, sires were chosen from the proportion selected during the first selection stage (performance testing), modeling a two-stage selection process. The effect on genetic gain and profitability of varying test capacity and number of progeny per sire and of ultrasound scanning of live animals was examined for all breeding schemes. Breeding schemes that selected young bulls during performance testing based on additional individual traits and information on carcass traits from their relatives generated additional genetic gain and profitability. Increasing test capacity resulted in an increase in genetic gain in all schemes. Profitability was optimal in Scheme 2 (a scheme similar to Scheme 1, but selection of young bulls also was based on information on carcass traits from their relatives) to 10 when 900 to 1,000 places were available for performance testing. Similarly, as the number of progeny used in the selection of sires increased, genetic gain first increased sharply and then gradually in all schemes. Profit was optimal across all breeding schemes when sires were selected based on information from 150 to 200 progeny. Additional genetic gain and profitability were generated in each breeding scheme with ultrasound scanning of live animals for carcass traits. Ultrasound scanning of live animals was more important than the addition of any other traits in the selection criteria. These results may be used to provide guidance to Japanese Black cattle breeders.  相似文献   

16.
Records from 7,200 separate closed herds with either 12 or 25 sows that were mated to either four or eight boars per year were simulated by computer. Effects of selection method, herd size, and contemporary group variability on average genetic change, genetic variance, and inbreeding over 10 yr of selection were analyzed for traits with heritabilities of .1, .3, and .6. Selection of replacement animals was on individual phenotype or BLUP of breeding value using a reduced animal model. For both of these selection methods, two culling schemes were imposed: 1) based only on involuntary culling because of losses due to conception rate and age and 2) when an available replacement animal was projected to be superior to an existing breeding animal in the herd in addition to the involuntary culling. The contemporary group standard deviation was set at either .1 or .5 of a phenotypic standard deviation. Selection with BLUP gave 72, 36, and 12% more genetic improvement for heritabilities of .1, .3, and .6, respectively, than selection on individual phenotype after 10 yr. However, inbreeding increased 20 to 52% more rapidly and there was a decrease in genetic variance. Culling based on Scheme 2 increased genetic improvement over Scheme 1 by about 75% with coincident increases in inbreeding level and decreases in genetic variance. The largest changes in inbreeding and genetic variance were associated with culling on BLUP. Culling when a superior animal was available with individual phenotype had little effect on inbreeding and genetic variance. Use of four boars rather than eight boars and 25 rather than 12 sows per herd increased genetic response. Use of four boars also increased inbreeding and decreased genetic variance. Genetic variance was higher in herds with 25 sows, but the size of the sow herd had little effect on inbreeding. Contemporary group variation influenced only the genetic response of individual phenotypic selection with culling.  相似文献   

17.
Inbreeding is known to affect metric traits. Reduction of additive genetic variance, as well as phenotypic values are its most significant deleterious effects. Yet the emergence of disorders due to recessive gene action constitutes another important aspect. Despite the fact that some effect of inbreeding can be positively used in selection schemes (T oro 1993), breeders are aware of the deleterious effects and try to avoid them. This is particularly true when the selection nucleus and the related population are of small size. Several authors (H agger 1991; V errier et al. 1993; W ray and G oddard 1994) have stressed that the application of sophisticated methods of selection, particularly BLUP-based techniques (H enderson 1973) is to be reconsidered in the light of inbreeding effects. Comparisons of selection methods should therefore account for inbreeding depression (T oro and P jrez -E nciso 1990; Q uinton et al. 1992). Other authors believe that inbreeding depression is not so important, at least in the meat production industry (G ama and S mith 1993) for traits with high heritabilities. Nevertheless, the net effect of inbreeding in a selection programme will depend on the magnitude of the selection response relative to the depression due to the accumulated inbreeding. Depending on whether genetic gain and inbreeding depression compensate for each other, the level of inbreeding of the animals may need to be accounted for in the selection process (K eller et al. 1989; R oehe et al. 1993; K lieve et al. 1994; B risbane and G ibson 1995). On the other hand, the response to inbreeding is not the same for all animals. There is an important range of variation for the estimates of inbreeding depression reported in the literature (e.g. L amberson and T homas 1984). Differences in such a response with respect to identifiable sources of variation should be examined. The objective of this work was to study the relationship between the depression due to inbreeding and litter size of ewes and weights of lambs; and to identify sources of a possible differential response to inbreeding between animals coming from different genetic line, sex, or type of birth.  相似文献   

18.
The aim of this study was to test whether the use of X-semen in a dairy cattle population using genomic selection (GS) and multiple ovulation and embryo transfer (MOET) increases the selection intensity on cow dams and thereby the genetic gain in the entire population. Also, the dynamics of using different types of sexed semen (X, Y or conventional) in the nucleus were investigated. The stochastic simulation study partly supported the hypothesis as the genetic gain in the entire population was elevated when X-semen was used in the production population as GS exploited the higher selection intensity among heifers with great accuracy. However, when MOET was applied, the effect was considerably diminished as was the exchange of females between the nucleus and the production population, thus causing modest genetic profit from using X-sorted semen in the production population. In addition, the effect of using sexed semen on the genetic gain was very small compared with the effect of MOET and highly dependent on whether cow dams or bull dams were inseminated with sexed semen and on what type of semen that was used for the bull dams. The rate of inbreeding was seldom affected by the use of sexed semen. However, when all young bull candidates were born following MOET, the results showed that the use of Y-semen in the breeding nucleus tended to decrease the rate of inbreeding as it enabled GS to increase within-family selection. This implies that the benefit from using sexed semen in a modern dairy cattle breeding scheme applying both GS and MOET may be found in its beneficial effect on the rate of inbreeding.  相似文献   

19.
Different modes of selection in dogs were studied with a special focus on the availability of disease information. Canine hip dysplasia (CHD) in the German shepherd dog was used as an example. The study was performed using a simulation model, comparing cases when selection was based on phenotype, true or predicted breeding value, or genomic breeding value. The parameters in the simulation model were drawn from the real population data. The data on all parents and 40% of their progeny were assumed to be available for the genetic evaluation carried out by Gibbs sampling. With respect to the use of disease records on progeny, three scenarios were considered: random exclusion of disease data (no restrictions, N), general exclusion of disease data (G) and exclusion of disease data for popular sires (P). One round of selection was considered, and the response was expressed as change of mean CHD score, proportion of dogs scored as normal, proportion of dogs scored as clearly affected and true mean breeding value in progeny of popular sires in comparison with all sires. When no restrictions on data were applied, selection on breeding value was three times more efficient than when some systematic exclusion was practised. Higher selection response than in the exclusion cases was achieved by selecting on the basis of genomic breeding value and CHD score. Genomic selection would therefore be the method of choice in the future.  相似文献   

20.
Findings within the last 15 years emphasize the possible role of genomic imprinting for trait expression in livestock species. In genetic evaluation, genomically imprinted traits can be treated by models with two different breeding values per animal; one accounts for the paternal and the other for the maternal expression pattern. Relative weighting factors for these breeding values were derived by a generalized version of the discounted gene flow method, which was extended to a gametic level to account for parent‐of‐origin effects. The gametic approach proved also useful for calculating the expected increase in inbreeding induced by one round of selection and its dynamics over time. The gametic gene flow method was applied to a hypothetical pig breeding programme. Relative weighting factors were higher for the paternally inherited genetic effect even in female selection paths, but depend on the breeding scheme heavily. The maximum medium‐term increase in inbreeding due to selection exceeded the long‐term increase in a range of 20–100%.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号