Pantoja J C F, Reinemann D J, Ruegg P L
Department of Dairy Science, University of Wisconsin, Madison 53706, USA.
J Dairy Sci. 2009 Oct;92(10):4978-87. doi: 10.3168/jds.2009-2329.
The objective of this study was to determine characteristics and associations among bulk milk quality indicators from a cohort of dairies that used modern milk harvest, storage, and shipment systems and participated in an intensive program of milk quality monitoring. Bulk milk somatic cell count (SCC), total bacteria count (TBC), coliform count (CC), and laboratory pasteurization count (LPC) were monitored between July 2006 and July 2007. Bulk milk samples were collected 3 times daily (n = 3 farms), twice daily (n = 6 farms), once daily (n = 4 farms), or once every other day (n = 3 farms). Most farms (n = 11) had direct loading of milk into tankers on trucks, but 5 farms had stationary bulk tanks. The average herd size was 924 cows (range = 200 to 2,700), and daily milk produced per herd was 35,220 kg (range = 7,500 to 105,000 kg). Thresholds for increased bacterial counts were defined according to the 75th percentile and were >8,000 cfu/mL for TBC, >160 cfu/mL for CC, and >or=310 cfu/mL for LPC. Means values were 12,500 (n = 7,241 measurements), 242 (n = 7,275 measurements), and 226 cfu/mL (n = 7,220 measurements) for TBC, CC, and LPC, respectively. Increased TBC was 6.3 times more likely for bulk milk loads with increased CC compared with loads containing fewer coliforms. Increased TBC was 1.3 times more likely for bulk milk with increased LPC. The odds of increased TBC increased by 2.4% for every 10,000-cells/mL increase in SCC in the same milk load. The odds of increased CC increased by 4.3% for every 10,000-cells/mL increase in SCC. The odds of increased CC increased by 1% for every 0.1 degrees C increase in the milk temperature upon arrival at the dairy plant (or at pickup for farms with bulk tank). Laboratory pasteurization count was poorly associated with other milk quality indicators. Seasonal effects on bacterial counts and milk temperature varied substantially among farms. Results of this study can be used to aid the interpretation and analysis of indicators of milk quality intensively produced by dairy processors' laboratories.
本研究的目的是确定一组使用现代牛奶采集、储存和运输系统并参与强化牛奶质量监测计划的奶牛场散装牛奶质量指标的特征及相互关系。在2006年7月至2007年7月期间对散装牛奶体细胞计数（SCC）、总细菌计数（TBC）、大肠菌群计数（CC）和实验室巴氏杀菌计数（LPC）进行了监测。散装牛奶样本的采集频率为每天3次（n = 3个农场）、每天2次（n = 6个农场）、每天1次（n = 4个农场）或每隔一天1次（n = 3个农场）。大多数农场（n = 11）将牛奶直接装入卡车的奶罐中，但有5个农场设有固定的散装奶罐。平均牛群规模为924头奶牛（范围 = 200至2700头），每个牛群每天产奶量为35220千克（范围 = 7500至105000千克）。细菌计数增加的阈值根据第75百分位数确定，TBC >8000 cfu/mL，CC >160 cfu/mL，LPC≥310 cfu/mL。TBC、CC和LPC的均值分别为12500（n = 7241次测量）、242（n = 7275次测量）和226 cfu/mL（n = 7220次测量）。与大肠菌群较少的牛奶相比，CC增加的散装牛奶中TBC增加的可能性高6.3倍。LPC增加的散装牛奶中TBC增加的可能性高1.3倍。在同一牛奶批次中，SCC每增加10000个细胞/mL，TBC增加的几率增加2.4%。SCC每增加10000个细胞/mL，CC增加的几率增加4.3%。牛奶运抵乳品厂时（或对于设有散装奶罐的农场，在装车时），牛奶温度每升高0.1摄氏度，CC增加的几率增加1%。实验室巴氏杀菌计数与其他牛奶质量指标的相关性较差。不同农场之间，细菌计数和牛奶温度的季节效应差异很大。本研究结果可用于辅助解释和分析乳品加工实验室集中生产的牛奶质量指标。
