Analysis Of Affected Factors And Estimation Of Genetic Parameters Of Urea Nitrogen In Holstein Cow Milk

Milk Urea Nitrogen(MUN)is an important indicator to measure the balance of energy nitrogen in dairy cows.In this study,a total of 80,988 test-day records of 12,443 Holstein cows from 30 cattle farms were used,and the data was from DHI Laboratory of Dairy Research Center of Shandong Academy of Agricultural Sciences.The effects of factors such as Day in Milk(DIM),calving season,lactation season,cattle farm and age on MUN were analyzed,and the genetic parameters of MUN and its correlation with milk yield and other traits were estimated,it provides scientific guidance for the development of more scientific,rational and cost-effective feed formulas and genetic improvement of dairy cows in production practice.(1)The effects of DIM,calving season,lactation season,cattle farm and age on MUN were analyzed,using the GLM program of SAS 9.2 software.The results showed that DIM,calving season,lactation season,cattle farm and age of months had a significant effect on MUN(P<0.01).(2)Using the DMU software and test-day repetitive force model,the genetic parameters of MUN and some milk-producing traits were estimated.The results showed that the heritabilities of MUN,milk yield,percentage of fat in milk,percentage of protein in milk and somatic cell score(SCS)were 0.10,0.07,0.09,0.12 and 0.02,respectively;and the repeatabilities were 0.01,0.29,0.10,0.17 and 0.19,respectively.The phenotype correlation of MUN with milk production,milk fat percentage,milk protein rate,and SCS were 0.44,0.11,0.08,and-0.02,respectively,and genetic correlations were-0.19,0.23,0.09,and-0.49,respectively.In conclusion,the MUN value is significantly affected by non-nutritive factors(DIM,calving season,lactation season,cattle farm and age).MUN increased with the increases of DIM.The MUN reached the highest at 150-180 d,after gradually decreased;the cows that were calved in spring and autumn had the highest MUN,followed by summer and winter.In winter,cows had the highest MUN,followed by summer and spring and autumn.Secondly,in the application of MUN to guide the management of cattle farms,the application of the DIM,calving season and lactation season environmental factors in the cattle is applied to carry out scientific guidance.The heritability of MUN was low.However,for milk production traits,environmental factors had a greater impact on it.In production practice,the control of environmental factors in cattle should be strengthened.