Association of Tumor Necrosis Factor Gene Polymorphisms with Milk Somatic Cell Score in Dairy Cattle

Mastitis is one of the most prevalent and costly diseases affecting dairy cattle production. In the present study, effects of tumor necrosis factor (alpha isomer) gene (TNF-α) polymorphisms on milk somatic cell count (SCS) and subclinical mastitis was investigated in 121 Holstein dairy cattle. The polymorphisms of a 303 bp fragment of TNF-α gene were investigated by PBR and PCR-SSCP techniques. The EcoRI did not digest the amplified segment and all the samples were monomorph. Therefore, the SSCP test was done on amplification products and three banding pattern (1, 2 and 3) were observed with frequencies of 3.3, 27.1 and 69.5%, respectively. Marker- trait analysis showed that, the first 70 days of milking period, different genotypes of TNF-α gene had significant effects on SCS and cows carrying banding pattern 2 had minimum sensitivity to SCS increment. Also, genotypes of TNF-α gene were significantly associated with SCS and banding pattern 1 showed minimum sensitivity to SCS increment at the end of milking period (from day 210 to 420). Association between different genotypes of TNF-α gene and SCS was not significant in the middle of milking period (from day 70 to 210). Also, in the present study, parity, milking months and their interaction had significant association with somatic cell score. The obtained results of the present study indicated that selection in faror of the banding patterns 1 and 2 might contribute to a reduction of SCS in Holstein dairy cattle.