تجزيه ژنتيكي صفت توليد شير دوره اول شيردهي و ارزيابي اثر انتخاب براي آن بر ارزش فنوتيپي سن نخستين زايش گاوهاي هلشتاين ايران با استفاده از رگرسيون كوآنتايل

Genetic analysis for the trait of first lactation milk production and evaluation of the impact of selection for it on the phenotypic value of age at first calving of Iranian Holsteins using quantile regression

ﻫﺪف از اﯾﻦ ﺗﺤﻘﯿﻖ، ﺗﺠﺰﯾﻪ ژﻧﺘﯿﮑﯽ ﺻﻔﺖ ﺗﻮﻟﯿﺪ ﺷﯿﺮ دوره اول ﺷﯿﺮدﻫﯽ و ارزﯾﺎﺑﯽ اﺛﺮ اﻧﺘﺨﺎب ﺑﺮاي آن ﺑﺮ ارزش ﻓﻨﻮﺗﯿﭙﯽ ﺳﻦ ﻧﺨﺴﺘﯿﻦ زاﯾﺶ ﮔﺎوﻫﺎي ﺷﯿﺮي اﯾﺮان ﺑﺎ اﺳﺘﻔﺎده از رﮔﺮﺳﯿﻮن ﮐﻮآﻧﺘﺎﯾﻞ ﺑﻮد. ﺑﺮاي اﯾﻦ ﻣﻨﻈﻮر، رﮐﻮردﻫﺎي ﺗﻮﻟﯿﺪ ﺷﯿﺮ دوره اول ﺷﯿﺮدﻫﯽ 327190 رأس ﮔﺎو ﺷﯿﺮي ﺷﮑﻢ زاﯾﺶ اول ﺣﺎﺻﻞ از 5260 رأس ﮔﺎو ﻧﺮ و 235172 ﮔﺎو ﻣﺎده( در 637 ﮔﻠﻪ ﮐﻪ ﻃﯽ ﺳﺎلﻫﺎي 1376 ﺗﺎ 1394 زاﯾﺶ داﺷﺘﻨﺪ، ﻣﻮرد اﺳﺘﻔﺎده ﻗﺮار ﮔﺮﻓﺖ. ﺗﺠﺰﯾﻪ ژﻧﺘﯿﮑﯽ ﺻﻔﺖ ﻣﺰﺑﻮر ﺑﺎ اﺳﺘﻔﺎده از ﯾﮏ ﻣﺪل دام اﻧﺠﺎم ﺷﺪ. در ﻣﺪل، آﺛﺎر ﺛﺎﺑﺖ اﺳﺘﺎن، ﮔﻠﻪ، ﺳﺎل و ﻣﺎه زاﯾﺶ، ﻣﺘﻐﯿﺮﻫﺎي ﮐﻤﮑﯽ ﺗﻌﺪاد روزﻫﺎي ﺷﯿﺮدﻫﯽ، ﺳﻦ ﻧﺨﺴﺘﯿﻦ زاﯾﺶ و درﺻﺪ ژن ﻫﻠﺸﺘﺎﯾﻦ، و اﺛﺮ ﺗﺼﺎدﻓﯽ ﮔﺎو ﮔﻨﺠﺎﻧﺪه ﺷﺪﻧﺪ. ﻣﺪل ﻣﺬﮐﻮر ﺑﺎ اﺳﺘﻔﺎده از ﻧﺮم اﻓﺰار DMU ﺑﺮ دادهﻫﺎ ﺑﺮازش داده ﺷﺪ. ﺗﺎﺑﻌﯿﺖ ﺳﻦ ﻧﺨﺴﺘﯿﻦ زاﯾﺶ ﺑﺮ ﺣﺴﺐ ارزش اﺻﻼﺣﯽ ﭘﯿﺶﺑﯿﻨﯽ ﺷﺪه ﺑﺮاي ﺻﻔﺖ ﺗﻮﻟﯿﺪ ﺷﯿﺮ دوره اول ﺷﯿﺮدﻫﯽ ﺑﺎ ﯾﮏ ﻣﺪل رﮔﺮﺳﯿﻮن ﮐﻮآﻧﺘﺎﯾﻞ ﻣﺤﺎﺳﺒﻪ ﺷﺪ. ﯾﺎﻓﺘﻪﻫﺎ ﻧﺸﺎن داد وراﺛﺖﭘﺬﯾﺮي ﺻﻔﺖ ﺗﻮﻟﯿﺪ ﺷﯿﺮ دوره اول ﺷﯿﺮدﻫﯽ ﺑﺮاﺑﺮ ﺑﺎ 0/276 ﺑﻮد. ﺑﻬﺒﻮد ژﻧﺘﯿﮑﯽ ﺳﺎﻻﻧﻪ در ﮔﺎوﻫﺎي زﯾﻨﻪ و اﺻﯿﻞ ﻫﻠﺸﺘﺎﯾﻦ ﺑﻪ ﺗﺮﺗﯿﺐ ﺑﺮاﺑﺮ ﺑﺎ 17/352 )R2=0/913( و 23/398 )R2=0/962( ﮐﯿﻠﻮﮔﺮم ﺑﻮد (0/0001

The main aim of the present research was the genetic analysis of the first lactation milk yield trait and evaluation of the impact of selection for milk on the phenotype of age at first calving in Iranian dairy cows using quantile regression. Lactation milk records of 327190 first parity cows (progeny of 5260 sires and 235172 dams) in 637 herds (in 15 provinces) and calved between 2007 and 2015 were utilized. Genetic analysis was carried out with the use of an animal model. In the model, fixed effects of the province, herd, year and month of calving, covariates of lactation length, age at first calving, percentage of Holstein gene, as well as the random effect of the cow were included. The model was fitted on the data using the DMU package. Regression of age at first calving on predicted breeding value was fitted through a quantile regression model. The findings revealed that the heritability of lactation milk yield was equal to 0.276. Annual genetic gain in grade and Holstein purebred were found to be 17.352 (R2=0.913) and 23.398 (R2=0.962) Kg, respectively (P<0.0001). All estimated regression coefficients were negative in different percentiles of age at first calving and ranged between -0.0009 and -0.0344 (month per Kg) which indicates that the influence of genetic potential of cows for milk yield on different parts of calving age distribution is not the same.