Wpływ struktury genetycznej stada na wskaźniki płodności i długość użytkowania samic szynszyli
AbstractFor last few decades the evaluation of population of genetic variability by using pedigree analysis has been one of the main topics in animal breeding. According to FAO regulations, since 1992 small native livestock populations should be treated as genetic resources of countries or regions. These regulations have obliged the regional or national authorities to develop a conservation strategy for these genetic resources, which, in turn, requires a detailed description of their genetic structure. In many countries a lot of research has been conducted to monitor genetic diversity of their native breeds of livestock and companion animals. The standard approach has been to estimate inbreeding and relationship coefficients to avoid inbreeding depression. Additionally, the effective population size and effective number of founders and ancestors have been calculated. In many small populations of breeding animals, the genetic structure proved to be poor and the increase in the level of inbreeding had a detrimental impact on the animal health, viability, fertility and production traits. However, similar problems have been reported on large populations of dairy cattle, when the number of sires decreased rapidly as a result of introducing artificial insemination. Genetic diversity and inbreeding depression have been investigated in many breeds of cattle, horses, sheep and goats, pigs, fur animals like foxes, minks or rabbits, or even dogs, but have never been studied in chinchillas. So the aim of the work was: 1) to examine the genetic structure of a large chinchilla herd, 2) to examine the influence of dam and litter inbreeding levels on the female lifetime performance, fertility and length of productive life, 3) to estimate heritability and genetic correlations of the female lifetime production and fertility traits and to analyze the effect of inbreeding on these genetic parameters. The data were pedigrees of 1603 chinchillas, 231 males and 1372 females, born in 1990-2010 and also information about 6442 litters, born in 1991-2010, from 1033 chinchilla dams. The pedigree analysis consisted on the estimation of the inbreeding and relationship coefficients for 1603 animals from the active population, for their 1531 ancestors and for all 3134 animals found in pedigrees. The effective number of founders and ancestors were evaluated twice assuming different reference populations. First, for all 1603 animals, for the 908 animals born in 2001-2004 and for the 496 animals born in 2005-2010. Such analysis was performed in order to assess the current genetic condition of the examined chinchilla population and to determine possible losses of the founder genes in time. The examined traits of the female lifetime reproductive performance included the total number of litters and kits born, the total number of litters and kits weaned and the total rearing efficiency of the dam. The analyzed fertility traits were: 1) by the number of days between female parties. For the statistical analysis, the SAS(R) package assumed the linear models of female lifetime performance traits included the effects of female birth year, coat color variety, female birth litter size class and the effect of female inbreeding as covariate. The linear models for female fertility analysis contained the following effects: litter birth year class, litter birth season, female parity number class, and litter inbreeding effects as covariate or coat color variety and effect of female inbreeding as covariate. The standard REML method was used in individual animal models for the estimation of the heritability and genetic correlations of female lifetime production traits included fixed effects of female year of birth, female birth litter size class and coat color variety class and also random effects of animal and error term and, optionally, the dam inbreeding effect as a covariate. The REML repeatability animal models for assessing the heritability and genetic correlations of female lifetime production traits included fixed effects of female year of birth, female birth litter size class and coat color variety class and also random effects of animal and error term and, optionally, the dam inbreeding effect as a covariate. The REML repeatability animal models for assessing the heritability and genetic correlations of female fertility traits contained fixed effects of litter birth years class, litter birth season class, female parity number class and random effects of the animal, permanent environment and random error and the linear regression of each trait on the age at kindling as a covariate. Optionally, these models included also the effects of dam and litter inbreeding as covariates. The inbreeding and relationship coefficients in the examined chinchilla population were, in general, low. The mean inbreeding coefficient for the active population reached 0.0034 and for the inbred animals 0.0166. The fraction of inbred animals was also low, between 15% and 25%. The average relationship coefficients for active population were 0.0104 for all pairs and 0.0231 for related pairs. The analysis of founders and ancestors contributions showed steadily narrowing genetic pool of the examined chinchilla population. The mean values of female lifetime production traits were: 6.2(±4.5) litters born, 5.7 (±4.2) litters weaned , 11.8(±8.7) kits born, 9.8 (±7.5) kits weaned and the total rearing efficiency of the dam reached 82.8%(±20.4%). The average values of female fertility traits for litter size were: 1.9(±0.8) kits born in the litter, 1.6(±0.9) kits weaned in the litter, 84.4%(±31.2%) rearing efficiency of each litter, 461.9(±301.6) interval. The mean length of chinchilla female productive life reached 1431 days (±872,5 days). There were seasonal differences in the number of litters an progeny born, in the litter size and in the length of kindling interval between season 1 (March-August) and season 2 (September-February). The analyzed traits of female productive life, expect for the total rearing efficiency of the dam, differed also between female birth year classes and color variety. The female fertility traits, except for the rearing efficiency of each litter, and the length of female productive life also showed similar differences. The inbred dams showed highly significant decrease in the total number of litters and progeny born and weaned, and lack of the effect of inbreeding on the total rearing efficiency. The female inbreeding did not influence the litter size born and weaned and the rearing efficiency of each litter. However, the inbred dams had significantly level influenced none of the female fertility traits, but it extended the length of female productive life. Heritability for female lifetime production traits were low and reached 0.153(±0.0005), 0.140(±0.0005), 0.148(±0.0005), 0.129(±0.0005) and 0.139(±0.0005) for the total number of litters born and weaned, for the total number of kits born and weaned and for the total rearing efficiency of the dam, respectively. The genetic correlations for the number of litter and progeny traits were high and positive, ranging between 0.924 and 0.985. Conversely, the correlations between the total rearing efficiency and other lifetime productivity traits were low and negative. The estimated inbreeding influence of 10% increase of female F x on female lifetime production traits were low and positive: +0.99 litter for the total number of litters born, +0.95 litter for the total number of litters weaned, +2.29 kits for the total number of kits born, +2.44 kits for the total number of kits weaned and +0.33% for the total rearing efficiency of the dam. The estimated genetic trends for the total rearing efficiency were negative in most of female birth years. The heritability assessed for female fertility traits were low and reached 3.130(±0.0001), 0.117(±0.0001), 0.012(±0.00003) and 0.016(±0.0001) for litter size born. Litter size weaned, rearing efficiency of each litter and kindling interval, respectively. The genetic correlation for both litter sizes was high and positive, reaching 0.935, and the correlations for rearing efficiency and litter sizes were low or moderate and negative, ranging between -0.097 and -0.439. Genetic correlations of kindling interval with other fertility traits were, in general, low and negative. The estimated inbreeding influence of 10% increase of female Fx on the female fertility traits was low, reaching -0.030 kits born in the litter, +0.029 kits weaned in the litter, +0.0014% for rearing efficiency of each litter and – 15.31 days for kindling interval. The estimated inbreeding influence of 10% increase of litter Fx on the female fertility traits were also low and reached -0.0016% for rearing efficiency of each litter and +2.33 days for kindling interval. Taking into account the low number of inbred females and litters and also their low values of inbreeding coefficients in the presented study, the problem of influence of inbreeding on fertility and length of productive life in chinchillas needs further analysis. Low levels of inbreeding detected in the examined population had rather positive effect on the examined traits, which confirms the deliberate breeding strategy in the herd.
|Other language title versions||The influence of the herd genetic structure on the chinchilla’s female fertility traits and length of productive life|
|Publisher||Wydawnictwo Uniwersytetu Rolniczego im Hugona Kołłątaja w Krakowie, MNiSW  [Uniwersytet Rolniczy im. Hugona Kołłątaja w Krakowie]|
|Publishing place (Publisher address)||Kraków|
|Book series /Journal (in case of Journal special issue)||Zeszyty Naukowe Uniwersytetu Rolniczego im. Hugona Kołłątaja w Krakowie. Rozprawy, ISSN 1899-3486, (0 pkt)|
|Publication size in sheets||9.2|
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