Research Of Relationship Of Somatic Cell Score And Resistance To Mastitis In Dairy Cow

Data were collected from Tianjin Dairy Cattle Development Center, containing 15421 records of DHI for 1973 cows from January in 2002 to March in 2004, records of body type classification for 1088 cows, and records of milk flow for 350 cows. Factors affecting SCS, type linear score and milk flow were analyzed by method of least squares, and the factors affecting significantly (P<0.05) were revised. Genetic parameters of 18 traits were estimated by half-sib correlation. Then resistance factors to mastitis were obtained by factor analysis with genetic correlation matrix.The results suggest that herd and calving season affect SCC and SCS significantly (P<0.05), year doesn't affect significantly SCC (P>.05) but affects SCS significantly (P<0.05), lactation number and month in milk affect SCC and SCS significantly (P<0.05), bull affect SCC and SCS significantly (P<0.01), bull affect SCC and SCS significantly (P<0.01) too. SCS affect milk fat percent and fat-corrected milk. Different herd, lactation number and month in milk affect type linear score differently. Bull affect type linear score significantly. Udder depth, udder cleft and fore udder attachment affect SCS significantly (P<0.05 or P<0.01). Lactation number and month in milk affect milk flow evalued by different evaluation methods discrepancy, but they affect average milk flow significantly which affects SCS significantly (P<0.05).Heritabilities estimated are from 0.04(foot angle) to 0.52 (front teat placement). Heritabilities of udder traits are moderate or high. Heritability of average milk flow estimated is 0.45. Genetic correlation between SCS and other traits estimated are from 0.03(heel depth) to -0.65(udder cleft), and genetic correlation between udder depth, udder cleft, fore udder attachment and SCS are negatively high.Eight factors are obtained from eighteen traits by factor analysis and cumulative is up to 69%. Udder health factor F1 is obtained, which is composed of udder depth, udder cleft, fore udder attachment and SCS. Foot&Leg health factor (or longevity factor) F2 consists of foot angle, foot heel depth and rear legs-rear view.Analysis results suggest: Fixed effects affect body type traits, somatic cell score and milk flow differently. Resistance to Mastitis and Longevity of dairy cows can be improved by selecting partial udder traits and Foot&Leg.