Evolution of the cellular quality of cow's milk: Description and factors of variation in two large herds subjected to tri-daily milking (Tunisian Sahel)

The present work, relating to a description of the Individual Cellular Counting (ICC) of the milk followed by an analysis of factors of cellular evolution, was carried out in two large cattle farms in a semi-arid environment (Sousse region, Tunisia). The first farm belongs to the private sector (Gloulou-Sidi Bou Ali) and the second one to the state sector (OTD-Enfidha), all subjected to indoors tri-daily mechanical milking. We have concluded that 25% of cows have an arithmetic average (AA) of > 200 000 cells/ml for ICC. The AA of cows ICC was 371 000 cells /ml, while the geometric average (GA) of cows ICC was only 107 500 cells /ml. The median was 73 000 cells /ml, value which is close to the GA and widely away from the AA, thus showing the utility of the GA. In both considered farms, the change in ICC was inversely proportional to milk production. However, ICC showed an increase with the rank of lactation, lactation stage and the spring calving season.

Keywords: Dairy bovine, Individual Cellular Counting, Descriptive analysis, Sources of cellular variability, Semi-arid littoral environment