Evaluation of raw milk quality in different production systems and periods of the year

The objective of this study was to evaluate the quality of raw milk in different production systems and its variation throughout the year. The data were collected from 943 dairy farms in the South, Central-West and Central regions of the state of Minas Gerais, and in Vale do Paraíba, in the state of São Paulo, Brazil. The data were collected in the period from January 2009 to September 2011, in a total of 18,206 samples. The properties were divided into confinement, semi-confinement and extensive production systems. The evaluated factors were somatic cell count (SCC), total bacterial count (TBC) and protein and fat contents. There was no effect of production system on the contents of protein, fat and SCC. Total bacterial count, however, was affected by production. Seasonal variations were found for SCC, TBC, protein and fat; the highest protein values were found from March to June; the highest fat contents were obtained from May to August; and TBC and SCC, from December to March. The production system does not interfere with the percentage of fat and protein and SCC of the milk. However, confinement systems present a better TBC content. Both month and year are factors that interfere with TBC, SCC, protein and milk fat, and the best patterns are found in the coldest periods of the year.

本研究旨在评估不同生产体系下生鲜乳的品质及其全年变化规律。研究数据采集自巴西米纳斯吉拉斯州（Minas Gerais）南部、中西部、中部区域以及圣保罗州（São Paulo）瓦莱杜帕拉伊巴（Vale do Paraíba）的943座奶牛场，采样时段为2009年1月至2011年9月，累计获取18206份生鲜乳样品。参试奶牛场被划分为舍饲、半舍饲与粗放养殖三种生产体系，本研究评估的指标包括体细胞数（Somatic Cell Count, SCC）、细菌总数（Total Bacterial Count, TBC）以及乳蛋白与乳脂肪含量。研究结果显示，生产体系对乳蛋白、乳脂肪含量与体细胞数无显著影响，但细菌总数则受生产体系的显著影响。进一步分析发现，体细胞数、细菌总数、乳蛋白含量及乳脂肪含量均存在季节性波动：乳蛋白含量峰值出现在3月至6月，乳脂肪含量峰值出现在5月至8月，而细菌总数与体细胞数的峰值则出现在12月至次年3月。生产体系不会对生鲜乳的乳脂肪、乳蛋白占比及体细胞数产生干扰，但舍饲体系下的生鲜乳细菌总数表现更优。此外，采样月份与年份均为影响细菌总数、体细胞数、乳蛋白及乳脂肪含量的显著因素，最优品质指标均出现在一年中气温较低的时段。