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The objective of this study was to evaluate the seasonal influence on the chemical composition, somatic cell count (SCC), and total bacterial count (TBC) of raw bulk-tank milk in northeastern Brazilian states. Data were obtained from milk samples from tanks collected monthly by industries registered with the Federal Inspection Service. According to normative instruction #62 (IN-62), two validity periods were considered. The highest recorded averages for chemical composition were between May and July. The mean fat content varied from 3.51% to 3.69%, and the protein content ranged from 3.07% to 3.17%. The averages of SCC ranged from 4.66 to 4.90 × 1,000 cells/ml, with the highest being recorded in July. At the same time, the TBC ranged from 2.34 to 2.53 cfu/ml. The highest TBC was recorded in March. The mean values of fat, protein, defatted dry extract, SCCs, and TBC were influenced by the months of the year. The means for these variables decreased in periods when Brazilian legislation was more severe. However, the SCC and TBC averages found in this study were still high, considering the quality of raw milk production. SCC and TBC presence still did not comply with the limits established by the legislation.

The aim of this study was to evaluate the statistical process control (SPC) as an identification tool of non-natural effects on milk quality, which may be manipulated. Data of milk production, somatic cell count (SCC) and total bacterial count (TBC) from 384 farms were used. Natural effects (season and volume) on the variation of SCC and TBC were evaluated; furthermore, control charts of somatic cell score (SCS) and total bacterial count transformed (TBCt) were designed to find non-natural variation resources on four farms. It was observed that the season affected significantly the SCS and TBCt. Control charts, in each season, indicated the non-natural variation in SCS and TBCt on the four farms evaluated. Therefore, the application of SPC as a tool at farm level is an additional instrument for monitoring milk quality.

The aim of this study was to use the statistical process control (SPC) as a tool of recognition and rating for farms with larger probabilities of infraction of milk quality standards used by industry. Data of somatic cell count (SCC) and total bacterial count (TBC) from 452 farms were used. Proportion of infractions of quality standard was calculated considering limits of SCC = 400,000 cells/mL and TBC = 100,000 CFU/mL. Indices Cpk were calculated and farms were rated according to four categories of Cpk means and indices. The farms which presented larger means and standard deviation had larger frequencies of violation. Farms with means lower than limits proposed to SCC and TBC represented, respectively, 25.05 % and 97.78 % of farms. However, proportion of farms that provided milk consistently within the quality standards evaluated (Cpk ≥ 1) represented 4.65 % and 35.17 % of farms for SCC and TBC, respectively. Therefore, the Cpk index can be used by the industry associated with the current models to characterize milk quality from farms, since it identifies more consistent herds in producing quality-standard milk.