Average Relatedness Coefficient Research Articles

Genetic diversity and population structure of Boer and Nubian goats in Mexico

In Mexico, since 2010 the Asociación Mexicana de Criadores de Ganado Caprino de Registro has been undertaking annual national genetic evaluations for the Boer and Nubian goat breeds. Mexican pedigree goat farmers are concerned with maintaining a reasonable high genetic diversity and a low level of inbreeding without loss of genetic gain. This study aimed to assess the genetic diversity and to describe the population structure of the Boer and Nubian goat breeds in Mexico using pedigree analyses to support the development of strategies for breeding programs. Herdbook information collected between 1994–2017 for Boer and from 1991 to 2017 for Nubian were utilized. The information included pedigree records on 18,947 animals for Boer (141 flocks) and 13,744 animals for Nubian (99 flocks). The effective number of founders ( f e ) were 504 and 203, and the effective number of ancestors ( f a ) were 253 and 88, for Boer and Nubian, respectively. The ratio f a / f e was 0.50 for Boer and 0.43 for Nubian, indicating the existence of population bottlenecks. The average inbreeding and relatedness coefficients were 1.02 and 0.28 % for Boer and, 1.39 and 1.04 % for Nubian. The number of most influential ancestors that explained 50 % of the genetic diversity in the population were 109 for Boer and 38 for Nubian. The average generation interval estimated through the four gametic paths was 3.27 ± 0.03 yr for Boer and 4.63 ± 0.06 yr for Nubian. Realized effective population size, computed from the individual increase in inbreeding, was 61.3 ± 24.5 for Boer and 69.3 ± 22.8 for Nubian (kids born from 2013 to 2017 were considered as the reference population for both breeds). The average equivalent completed generations, as a measure of pedigree completeness, were 2.02 for Boer and 2.88 for Nubian. The pedigree completeness index increased over time for both breeds. The results revealed the loss of genetic diversity and the presence of genetic bottlenecks for both populations. The study of the genetic diversity on these populations must continue to prevent the decrease in genetic progress and genetic variability. Additionally, a mating policy that simultaneously allows low levels of inbreeding, high levels of genetic diversity and maximum genetic progress, must be designed.

Population structure of Simmental beef cattle using pedigree analysis.

The purpose of this study was to estimate parameters related to the population structure and genetic diversity in the Simental breed based on the pedigree information of 77,553 animals. The individual coefficients of inbreeding and average relatedness, number of complete generations, coefficient of change of inbreeding, effective size, effective number of founders, number of ancestors and generation interval were calculated. Using the Simmental cattle information, the mean inbreeding and average relatedness coefficients were 1.49% and 0.99%, respectively. The effective number of founders and ancestors was 163 and 132, respectively, and the effective population size was 48.03. Despite the relatively small inbreeding coefficient, some of the estimated population parameters indicated the need to adopt measures to maintain the genetic variability of the population.

Genetic diversity and population structure estimation of Brazilian Somali sheep from pedigree data

The aim of this study was to describe and analyze the genetic diversity and population structure of Brazilian Somali sheep using pedigree records. Pedigree data of 9,038 individuals born between 1972 and 2018 were analyzed for completeness, gene origin probability, average relationship coefficient (AR), inbreeding coefficient, and genetic conservation index (GCI), using ENDOG v4.8 software. A total of 69.59%, 56.43%, 48.64%, 42.77%, and 34.05% of the examined individuals had pedigrees in the first, second, third, fourth and fifth ancestry, respectively. The total number of founders and ancestors was 833 and 837, whereas the effective number of founders and ancestors was 26 and 22, respectively. The eight main ancestors explained 51.04% of the total genetic variability. The AR and average inbreeding coefficient were 4.05 and 8.74, respectively. The mean GCI was 4.08, ranging from 1.00 to 17.43; three individuals showed a GCI above 17. In conclusion, the Brazilian Somali sheep show considerably high inbreeding coefficients, particularly those individuals born within the last decades. In contrast, some individuals have a high proportion of effective founders in their pedigrees, which can be used strategically for maintaining the genetic diversity of the breed.

Low genetic diversity in captive populations of the critically endangered Blue-crowned Laughingthrush (Garrulax courtoisi) revealed by a panel of novel microsatellites.

BackgroundCaptive populations permit research and conservation of endangered species in which these efforts are hardly implemented in wild populations. Thus, analysing genetic diversity and structure of captive populations offers unique opportunities. One example is the critically endangered Blue-crowned Laughingthrush, Garrulax courtoisi, which has only two known wild populations in Wuyuan, Jiangxi and Simao, Yunnan, China. We carried out the first conservation genetic study, in order to provide useful implications that allow for successful ex situ conservation and management of the Blue-crowned Laughingthrush.MethodsUsing the novel microsatellite markers developed by whole-genome sequencing, we genotyped two captive populations, from the Ocean Park Hong Kong, which are of unknown origin, and the Nanchang Zoo, which were introduced from the Wuyuan wild population since the year 2010–2011, respectively. The genetic diversity of captive Blue-crowned Laughingthrush populations was estimated based on genetic polymorphisms revealed by a new microsatellite data set and mitochondrial sequences. Then, we characterised the population structure using STRUCTURE, principal coordinates analysis, population assignment test using the microsatellite data, and haplotype analysis of mitochondrial data. Additionally, we quantified genetic relatedness based on the microsatellite data with ML-Relate.ResultsOur results showed equally low levels of genetic diversity of the two captive Blue-crowned Laughingthrush populations. The population structure analysis, population assignment test using the microsatellite data, and haplotype analysis of the mitochondrial data showed weak population structuring between these two populations. The average pairwise relatedness coefficient was not significant, and their genetic relatedness was quantified.DiscussionThis study offers a genetic tool and consequently reveals a low level of genetic diversity within populations of a critically endangered bird species. Furthermore, our results indicate that we cannot exclude the probability that the origin of the Hong Kong captive population was the wild population from Wuyuan. These results provide valuable knowledge that can help improve conservation management and planning for both captive and wild Blue-crowned Laughingthrush populations.

Population structure of Lori-Bakhtiari sheep in Iran by pedigree analysis

The objective of this study was to describe the population genetic structure and evaluate the state of conservation of genetic variability of Lori-Bakhtiari sheep in Iran. As such, pedigree information of 10,644 lambs lambed from 1989 through 2016 in the stud flock of Lori-Bakhttiari sheep was included in the analysis. Our first goal was to estimate mean and variance of family size across sires and dams using pedigree data. Our second goal was to estimate population structure in Lori-Bakhtiari sheep including estimation of pedigree completeness (PC), genetic conservation index (GCI), effective population size (Ne), effective number of founders (fe), effective number of ancestors (fa), generation interval (L), individual inbreeding coefficient (F) and average relatedness coefficient (AR) using the ENDOG software. The results showed that the average number of progenies per ram and ewe in their lifetime were 26.44 (15–152) and 3.6 (1–15), respectively. The mean and variance of family size of sires differ across years. The pedigree completeness (PC) was equal to 0.61. The fe and fa were 109 and 98, respectively with a ratio of 1.11. The number of ancestors explaining 50% of genetic diversity was 30. The Ne also varied from 142.68 to 144.13 during the study period. The average generation interval was 4.11 years. The mean inbreeding coefficient was 2.5% in inbred lambs and 1.26% in whole population with an annual increase of 0.09% per year and 0.87% per generation. The AR of the total population was estimated to 2.27% with an incremental trend of 0.10% per year and 0.59% in each generation. The average GCI was 11.75 units with an incremental trend of 0.76 per year. The effects of birth type and year of birth were found to be significant on most of the studied demographic parameters. Though there is an increasing inbreeding coefficient trend over a number of generations, it is still lower than the maximum acceptable recommendation of 1% per generation. This provides us an opportunity for maintaining genetic diversity and implementation of the improvement breeding program. However, unbalanced use of rams led to the creation of family size variation over years. Therefore, this study warrants a comprehensive mating plan with minimum inbreeding rate to maintain genetic variability in Lori-Bakhtiari sheep.

Analysis of founders and performance test effects on an autochthonous horse population through pedigree analysis: structure, genetic variability and inbreeding

The Maremmano is an autochthonous Italian horse breed, which probably descended from the native horses of the Etruscans (VI century B.C.); the Studbook was acknowledged in 1980, and it includes 12 368 horses born from that year up to 2015. The aim of this study was to evaluate the effect of the selection program on the genetic variability of the Maremmano population; the analysis was performed using both the ‘Endog v 4.8’ program available at http://webs.ucm.es/info/prodanim/html/JP_Web.htm and in-house software on official pedigree data. Four Reference Populations were considered, and the most important one was the population of the 12 368 Maremmano horses officially registered in the National Studbook. The pedigree completeness of this population was very good because it was more than 90% at the third parental generation and more than 70% at the fifth generation; the pedigree traced back to a maximum of 10.50 generations with an average of 3.30 complete generations and 5.70 equivalent complete generations. The average generation interval was 10.65±4.72 years, with stallions used for longer periods than mares. The intervals ranged from 10.15±4.45 (mother–daughter) to 10.99±4.93 (father–daughter). The effective number of founders (fe) was 74 and the effective number of ancestors (fa) was 30 so that the ratio fe/fa was 2.47. The founder genome equivalents (fg) was 13.72 with a ratio fg/fe equal to 0.18. The mean of the genetic conservation index was 5.55±3.37, and it ranged from 0.81 to 21.32. The average inbreeding coefficient was 2.94%, with an increase of 0.1%/year, and the average relatedness coefficient was 5.52%. The effective population size (Ne) computed by an individual increase in inbreeding was 68.1±13.00; the Ne on equivalent generations was 42.00, and this value slightly increased to 42.20 when computed by Log regression on equivalent generations. The analysis confirmed the presence of seven traditional male lines. The percentage of Thoroughbred blood in the foals born in 2015 was 20.30% and has increased 0.21%/year since 1980; in particular, it increased more than twice (0.51%/year) until 1993 and afterwards slightly fluctuated. The pedigree analysis confirmed the completeness of genealogical information and the traditional importance that breeders gave to the male lines; although the genetic diversity of Maremmano seemed to be not endangered by the selection program, some effects on the population structure were found and a more scientific approach to genetic conservation should be incorporated in the selection plans.

Network of families in a contemporary population: regional and cultural assortativity

Using a large dataset with individual-level demographic information of almost 60,000 families in contemporary Finland, we analyse the regional variation and cultural assortativity by studying the network between families and the network between kins. For the network of families the largest connected component is found to consist of around 1000 families mostly originated from one single region in Western Finland. We characterize the networks in terms of the basic structural properties. In particular, we focus on the k-cores and the presence of transitive triangles. Clustering in the networks is found to result from homophily by language and religious affiliations. The large network fragments appear to be small-worlds. We also compare the fragments in the kin network with respect to the average coefficient of relationship. The measures of assortativity are able to distinguish the families in terms of their regions of origin. Overall, we distinguish between two patterns of regional effects, the ‘metropolitan’ and the ‘cultural’ pattern.

Pedigree analysis and inbreeding effects over morphological traits in Campolina horse population

Genetic improvement, without control of inbreeding, can go to loss of genetic variability, reducing the potential for genetic gains in the domestic populations. The aim of this study was to analyze the population structure and the inbreeding depression in Campolina horses. Phenotype information from 43 465 individuals was analyzed, data provided by the Campolina Breeders Association. A pedigree file containing 107 951 horses was used to connected the phenotyped individuals. The inbreeding coefficient was performed by use of the diagonal of the relationship matrix and the genealogical parameters were computed using proper softwares. The effective population size was estimated based on the rate of inbreeding and census information, and the stratification of the population was verified by the average relationship coefficient between animals born in different regions of Brazil. The effects of inbreeding on morphological traits were made by the use of inbreeding coefficient as a covariate in the model of random regression. The inbreeding coefficient increased from 1990 on, impacting effective population size and, consequently, shrinking genetic variability. The paternal inbreeding was greater than maternal, which may be attributed to the preference for inbred animals in reproduction. The average genetic relationship coefficient of animals born in different states was lower than individuals born within the same state. The increase in the inbreeding coefficient was negatively associated with all studied traits, showing the importance to avoid genetic losses in the long term. Although results do not indicate a severe narrowing of the population until the present date, the average relationship coefficient shows signs of increase, which could cause a drastic reduction in genetic variability if inbred mating is not successfully controlled in the Campolina horse population.

Population genetic structure of Santa Inês sheep in Brazil.

This study aimed to describe the population genetic structure and evaluate the state of conservation of the genetic variability of Santa Inês sheep in Brazil. We used pedigree data of the Santa Inês breed available in electronic processing of the Brazilian Association of Sheep Breeders. A file with 20,206 records, which enabled the calculation of the genetic conservation index (GCI), individual inbreeding coefficient (F), change in inbreeding (ΔF), effective population size (Ne), effective number of founders (ƒe), effective number of ancestors (ƒɑ), generation interval (L), average relatedness coefficient of each individual (AR), and Wright's F-statistics (F IT, F IS, and F ST). For pedigree analysis and calculation of population parameters, the program ENDOG was used. The average inbreeding coefficient ([Formula: see text]) was 0.97% and the mean average relatedness ([Formula: see text]) 0.49%. The effective numbers of founders and ancestors were, respectively, 199 and 161. The average values of F and AR increased significantly over the years. The effective population size fluctuated over the years concurrently to oscillations in inbreeding rates, wherein N e reached just 68 in the year 2012. The mean average generation interval was 5.3years. The Santa Inês breed in Brazil is under genetic drift process, with loss of genetic variation. It requires the implementation of a genetic management plan in the herd, for conservation and improvement of the breed.

Population structure and genetic variability of the Segureña sheep breed through pedigree analysis and inbreeding effects on growth traits

Pedigree information on 37,459 sheep of the Segureña breed was used to evaluate population structure, genetic variability and the inbreeding effect on growth traits. The relation between the effective number of founders/ancestors (1.12) indicates that the founding animals contributed throughout the entire breed-forming process. The low values obtained for inbreeding (0.60%) and average relatedness coefficients (0.06%) indicate genetic variability; however, these results might be related to the low pedigree depth observed through the number of equivalent generations (1.23). Fixation indices (F-statistic) and the absence of nucleus herds indicate that, despite the intense use of some rams, population subdivision was not observed in the breed (FST=0.0183). Inbreeding depression was not observed on evaluated growth traits, with environmental factors, year-season-herd, type of birth and sex as primarily responsible for the observed variation.

Population structure of Mazandaran native fowls using pedigree analysis.

The objective of this study was to use pedigree analysis to evaluate the population structure and genetic variability of the Mazandaran native fowls in Iran by quantifying the pedigree completeness index, effective population size, genetic diversity, inbreeding level, and individual increase in inbreeding. The pedigree completeness analysis showed 3.31 full, 10.19 maximum, and 6.30 equivalent generations. The effective number of founders (f e) was 131, representing 5% of the potential number of founders. The effective number of ancestors (f a) was 81, and the genetic contribution of the 37 most influent ancestors explained 50% of the genetic variability in the population. The ratio f e/f a (effective number of founders/effective number of ancestors), which expresses the effect of population bottlenecks, was 1.62. The inbreeding coefficient increased over generations and the average was 1.93%. The average relatedness coefficient between individuals of the population was estimated to be 2.59%. The effective population size, based on the number of full generations, was 56. Family size analysis showed that fewer males than females were used, resulting in the observed levels of inbreeding. Average inbreeding coefficient in the Mazandaran native fowls can be regarded to be below critical levels. However, considering the relationship coefficients of individuals is recommended to aid maintaining genetic diversity of Mazandaran native fowls.

Partial genotyping at polymorphic markers can improve heritability estimates in sibling groups

Accurate estimates of heritability (h2) are necessary to assess adaptive responses of populations and evolution of fitness-related traits in changing environments. For plants, h2 estimates generally rely on maternal progeny designs, assuming that offspring are either half-sibs or unrelated. However, plant mating systems often depart from half-sib assumptions, this can bias h2 estimates. Here, we investigate how to accurately estimate h2 in nonmodel species through the analysis of sibling designs with a moderate genotyping effort. We performed simulations to investigate how microsatellite marker information available for only a subset of offspring can improve h2 estimates based on maternal progeny designs in the presence of nonrandom mating, inbreeding in the parental population or maternal effects. We compared the basic family method, considering or not adjustments based on average relatedness coefficients, and methods based on the animal model. The animal model was used with average relatedness information, or with hybrid relatedness information: associating one-generation pedigree and family assumptions, or associating one-generation pedigree and average relatedness coefficients. Our results highlighted that methods using marker-based relatedness coefficients performed as well as pedigree-based methods in the presence of nonrandom mating (i.e. unequal male reproductive contributions, selfing), offering promising prospects to investigate insitu heritabilities in natural populations. In the presence of maternal effects, only the use of pairwise relatednesses through pedigree information improved the accuracy of h2 estimates. In that case, the amount of father-related offspring in the sibling design is the most critical. Overall, we showed that the method using both one-generation pedigree and average relatedness coefficients was the most robust to various ecological scenarios.

Population genetic structure in the Holstein breed in Brazil.

We evaluated the population genetic structure of the Holstein breed in Brazil through pedigree analysis with the aim of supporting genetic management of extant herds. We used data from genealogical records of 204,511 animals in farms from south and southeast Brazil. Pedigree records between 1943 and 2005 were divided into seven periods of 8years to estimate the effective population size (N e ). N e varied during the study periods, ranging from 0.19 to 3016.25. There was an increase in the percentage of inbred animals over time, from 0.18 to 5.0%. However, this figure may be an underestimate due to the low completeness of pedigree, primarily related to paternal pedigree. The effective number of founders (fe) was 473 animals and ancestors (fa) was 471. The genetic contribution of 260 ancestors (founders or not) accounted for 50% of the genetic variability in the population. The average relatedness coefficient (AR) and inbreeding coefficient indicate that the Holstein breed in Brazil is being effectively managed, despite a moderate founder effect and the low number of animals that are responsible for the population variance.

Genetic Structure Analysis of Tatra Shepherd Dog Population From Tatra Mountain Region

Abstract The aim of the work was to analyze the genetic structure of the population of Tatra Shepherd dogs, registered in branches of Polish Kennel Club from Tatra Mountain Region. Data were pedigrees of 102 Tatra Shepherd dogs (33 males and 69 females) born between 1994 and 2011. Inbreeding and relationship coefficients, as well as effective number of founders and ancestors, were calculated. These statistics give the picture of genetic diversity of the population. Average inbreeding coefficient was 7.17%, whereas average relationship coefficient was 18.20%. The number of inbred animals and the mean FX values steadily increased over time. Twenty-six of 80 inbred animals had inbreeding coefficients higher than 10%. The effective number of founders was relatively high in relation to the population size (the effective number of ancestors was four times lower) and both were similar to the results of studies of other authors on different dog breeds. The total contribution of only 4 ancestors was enough to explain 50% of the gene pool of the population. Therefore, mating of related animals should be avoided in order to prevent the further increase of inbreeding level, because almost all Polish and foreign Tatra Shepherd dogs living now originate from the population under study.

Estrutura populacional da raça Girolando

O objetivo neste estudo foi avaliar a estrutura genética da população de bovinos da raça Girolando no Brasil. Analisou-se o arquivo de pedigree de 26.969 animais, composto de 3.031 machos e 23.938 fêmeas. O nível de conteúdo de informação do pedigree na geração atual foi 61%, mostrando ser de qualidade moderada. O coeficiente de endogamia médio e o coeficiente de relação médio da população Girolando foram 0,11 e 0,13%, respectivamente. O tamanho efetivo da população, considerando a geração completa traçada, foi 188, acima do nível crítico. Do total de 9.457 ancestrais que contribuíram para a população de referência, 457 explicaram 50% da variabilidade genética da população. O número efetivo de fundadores foi 551 e o de ancestrais 393. O intervalo médio de geração foi de 5,26 anos, sendo ligeiramente maior nas trilhas gaméticas mãe-filho e pai-filha. A partir dos coeficientes estimados, pode-se concluir que a endogamia nos rebanhos da raça Girolando foi de pequena magnitude e que as práticas de acasalamento foram adequadas durante o período avaliado. No entanto, é importante continuar com o monitoramento desses coeficientes a fim de prevenir perda de variabilidade genética

Genetic diversity of a nucleus flock of Malpura sheep through pedigree analyses

Malpura sheep is one of the heaviest sheep breed of India, known for its adaptability to harsh environment and potential for high meat production. It is distributed in the semi-arid region of Rajasthan, India. The pedigree information estimated by the number of equivalent generation traced was good (7.21). For reference cohort, effective number of founders (fe) was 58, representing 29.15% of the potential number of founders. The effective number of ancestors (fa) was 36 and the genetic contribution of the 13 most influent ancestors explained 50% of the genetic variability in reference cohort. The realised effective population size of the flock was 91.74±2.02. The ratio fe/fa which expresses the effect of population bottlenecks was 1.61. The average inbreeding coefficient for reference population was 3.32%. The average relatedness coefficient between individuals of the reference population was 5.10%. The generation interval was lowest for ram daughter pathway (2.72 years) and highest for ewe to son (4.13 years). Study revealed non-significant effect of individual inbreeding or change in inbreeding on the lamb live weights. Introduction of new sires with the lowest possible average relatedness coefficient and the use of appropriate mating strategies are recommended to keep inbreeding at acceptable levels and increase the genetic variability.

Practical aspects of genetic management of small populations – The Olkuska sheep example

The study aimed to identify important factors threatening genetic diversity within small sheep populations, and to propose sustainable management strategies. Demographic evolution, genetic diversity and current genetic management practices were analyzed in a population of Polish Olkuska sheep. Unbalanced contributions of individual rams to the next generation were observed due to differences in the period of their utilization, the number of progeny and the number of daughters used in reproduction. Matings between closely related animals were common. Pedigree completeness was satisfactory and inbreeding coefficient was high, 11.71% for lambs born in 2012. Relatively high values of potential and realized coancestries within flocks showed the importance of keeping more than one ram. The genetic conservation index and average relatedness coefficient, and their comparison between regions was helpful in considering management options. The information on genetic relationships and genetic conservation parameters of rams should be provided to breeders with simple interpretations.

Parâmetros populacionais da raça ovina Santa Inês no Brasil

O objetivo deste trabalho foi avaliar a estrutura populacional de ovinos da raça Santa Inês criados no Brasil. Foram utilizados dados de pedigree de 13.216 animais, pertencentes a 53 rebanhos de oito estados brasileiros, nascidos no período de 1976 a 2010. O programa Endog foi utilizado para análise do pedigree e estimação dos parâmetros populacionais. Do total de animais estudados, 80,86% apresentaram pedigree na primeira ascendência, 73,78% na segunda e 67,75% na terceira. O número máximo de gerações conhecidas foi de 19, e a média de gerações equivalentes foi de 4,67. A média do intervalo de gerações foi de 3,22±1,77 anos. O tamanho efetivo da população apresentou média de 172,5 animais. O número de animais fundadores foi 829, mas o número efetivo de fundadores foi apenas 50. Os 17 principais ancestrais explicaram 50% da variabilidade genética total. O coeficiente médio de relação foi de 3,87% e o de endogamia, de 6,92%. Apesar do satisfatório coeficiente médio de endogamia nas últimas gerações, este coeficiente requer monitoramento por sua proximidade do limite recomendável. O fluxo de genes entre os rebanhos é o principal fator para o aumento do tamanho efetivo e a manutenção da variabilidade genética da raça Santa Inês.

Utilização de pedigree para o monitoramento do programa de conservação da raça local de suíno Piau

A raça local brasileira Piau é um suíno tipo banha a qual passou por um processo de seleção realizado pelo médico veterinário Antonio Teixeira Vianna em 1939, com o intuito de desenvolver um animal de dupla aptidão, em outras palavras que fosse adequado para a produção de carne e gordura. As principais características da raça são rusticidade, adaptabilidade e resistência a doenças. O status de conservação da raça é ameaçado e em 1998 a Granja de Melhoramento de Suínos da Universidade Federal de Viçosa (UFV, Viçosa, MG, Brazil) iniciou uma criação de suínos da raça Piau com o objetivo de conservá-la e utilizá-la em estudos genéticos. O objetivo do presente estudo é descrever o programa de conservação da raça Piau da UFV e avaliar uma série de parâmetros populacionais, a fim de gerar informações que possibilitem o monitoramento e a melhoria do programa. Para a análise da estrutura populacional foi utilizado arquivo de pedigree com 1349 indivíduos por meio do software ENDOG v. 4.8. O programa de conservação da raça possui boa estrutura com registro de dados zootécnicos e pedigree desde a introdução dos primeiros animais na granja de melhoramento de suínos, juntamente com o controle de acasalamentos, o qual é baseado no acasalamento de animais com menor coancestralidade e na manutenção das famílias fundadoras. A população de Piau avaliada possui número efetivo de fundadores e ancestrais iguais a 9 e 8, respectivamente. O coeficiente de endogamia médio, coeficiente de relação médio e tamanho efetivo da população são 6,55 %, 19,74 % e 18,59, respectivamente. De acordo com os parâmetros avaliados é recomendado aumentar o tamanho efetivo da população, por meio da introdução de animais de outra população, uma vez que o pequeno número de fundadores torna difícil o controle da endogamia.

Population structure of Nellore cattle in northeastern Brazil

The objective of this study was to evaluate the population genetic structure of Nellore cattle in northeastern Brazil. Pedigree information was collected from 175,231 animals born from 1967 to 2007. Probability of gene origin, inbreeding, average relatedness coefficient (AR), completeness pedigree, effective population size and generation interval were calculated. Generation interval was high due to the long period of time animals were used as reproducers. The bottleneck effect was evidenced as a result of intensive use of limited breeders over the last years. Low values were observed in the effective number of founder animals (434) and ancestors (427) comparing with the number on the base (175,231) and reference populations (130,038). Generally, the variability explained by the founders and ancestors is considered low. The average coefficient of inbreeding (0.11%) and AR (0.14%) estimated for this population is considered low and can be partly explained by the increased population effective number in recent periods; however, it may be underestimated by shallow pedigree.