Binabaj Fateme Bahri, Farhangfar Seyyed Homayoun, Jafari Majid
Department of Animal Science, College of Agriculture and Natural Resources, Gonbad Kavous University, Gonbad Kavous, PO Box 163, Iran.
Department of Animal Science, College of Agriculture, University of Birjand, Birjand 9717434765, Iran.
Anim Biosci. 2021 Apr;34(4):506-515. doi: 10.5713/ajas.19.0642. Epub 2020 Feb 25.
Initial consequence of inbreeding is inbreeding depression which impairs the performance of growth, production, health, fertility and survival traits in different animal breeds and populations. The effect of inbreeding on economically important traits should be accurately estimated. The effect of inbreeding depression on growth traits in sheep has been reported in many breeds. Based on this, the main objective of the present research was to evaluate the impact of inbreeding on some growth traits of Iranian Baluchi sheep breed using quantile regression model.
Pedigree and growth traits records of 13,633 Baluchi lambs born from year 1989 to 2016 were used in this research. The traits were birth weight, weaning weight, six-month weight, nine-month weight, and yearling weight. The contribution, inbreeding and co-ancestry software was used to calculate the pedigree statistics and inbreeding coefficients. To evaluate the impact of inbreeding on different quantiles of each growth trait, a series of quantile regression models were fitted using QUANTREG procedure of SAS software. Annual trend of inbreeding was also estimated fitting a simple linear regression of lamb's inbreeding coefficient on the birth year.
Average inbreeding coefficient of the population was 1.63 percent. Annual increase rate of inbreeding of the flock was 0.11 percent (p<0.01). The results showed that the effect of inbreeding in different quantiles of growth traits is not similar. Also, inbreeding affected differently on growth traits, considering lambs' sex and type of birth.
Quantile regression revealed that inbreeding did not have similar effect on different quantiles of growth traits in Iranian Baluchi lambs indicating that at a given age and inbreeding coefficient, lambs with different sex and birth type were not equally influenced by inbreeding.
近亲繁殖的初始后果是近亲繁殖衰退，这会损害不同动物品种和群体在生长、生产、健康、繁殖力和生存性状方面的表现。应准确估计近亲繁殖对经济重要性状的影响。许多品种的绵羊中都报道了近亲繁殖衰退对生长性状的影响。基于此，本研究的主要目的是使用分位数回归模型评估近亲繁殖对伊朗俾路支绵羊品种某些生长性状的影响。
本研究使用了1989年至2016年出生的13633只俾路支羔羊的系谱和生长性状记录。这些性状包括出生体重、断奶体重、六个月龄体重、九个月龄体重和一岁龄体重。使用贡献、近亲繁殖和共同祖先软件来计算系谱统计数据和近亲繁殖系数。为了评估近亲繁殖对每个生长性状不同分位数的影响，使用SAS软件的QUANTREG过程拟合了一系列分位数回归模型。还通过对羔羊近亲繁殖系数与出生年份进行简单线性回归来估计近亲繁殖的年度趋势。
该群体的平均近亲繁殖系数为1.63%。该羊群近亲繁殖的年增长率为0.11%（p<0.01）。结果表明，近亲繁殖对生长性状不同分位数的影响并不相似。此外，考虑到羔羊的性别和出生类型，近亲繁殖对生长性状的影响也不同。
分位数回归表明，近亲繁殖对伊朗俾路支羔羊生长性状的不同分位数没有相似的影响，这表明在给定年龄和近亲繁殖系数下，不同性别和出生类型的羔羊受近亲繁殖的影响并不相同。
