Seasonal trends and milking-related factors influencing somatic cell counts in tank milks of dairy cattle in northeast Algeria

The present study aims to assess the relationship between the season and milking practices of dairy cows with collective milk quality by measuring Bulk Tank Milk Somatic Cell Count (BTM SCC). Samples were obtained monthly from 33 Holstein-Friesian dairy farms over a period of 12 months The 396 samples were tested by Direct Microscopic Somatic Cell Count (DMSCC) then allocated into two groups: low BTMSCC<200,000 cells/ml and high BTM SCC >200,000 cells/ml to explore the milking risk factors. The mean BTM SCC was 307,774 +/- 125,076cells/ml. All mean BTM SCC produced for the four seasons were > 200,000 cells/ml and summer season showed the highest levels. High BTM SCC was associated to the following milking risk factors: presence of chronically infected mastitis cows in the herd (P<0.001), failure of milking order depending on udder health (p=0.01), dirty milking place (p<0.001), and dirty teat at Cups On (p=0.07). Regarding the pre-milking procedures, preparing time per cow to allowed milk "Let Down" higher than 90s (p<0.001) and failure of pre-milking stripping (p<0.05) were the potential risk factors for high BTM SCC. However, both modalities of the pre-milking udder disinfection and teat drying were associated with high BTM SCC, which influenced milk quality independently in them. For the post-milking procedures, lack of hand-stripping for residual milk (p<0.001), lack of post-milking disinfection (p=0.01) and over/under milking (p=0.01) were significantly associated to high BTM SCC. Finally, high frequency of dairy farms with high BTM SCC was associated to medium milking machine rubberware condition and medium to high air adsorption during application of teat cups. All survived dairy farms practiced interim cleaning of milk units, used milking machine with bucket for transporting milk and semi-automatic technique for cups removal. High association level of these milking practices with the high BTM SCC had been shown. This study emphasized the need for adoption of stricter milking and herd management practices although considering the significant seasonal effect to consistent reductions in BTM SCC.