Variation in the milk serum proteome within and between individual cows

The objective of this observational study was to determine the variation between and within cows for their milk serum proteome. We used two sample sets to investigate the individual variations in milk serum proteome. Sample set 1 were mature milk with 5 times points collected between 2 months after the start and 2 months before the end of lactation. The information of diet, SCC and parity were recorded. Sample set 2 consisted of 17 mature milk samples, being in the same range of lactation days. Sample sets were prepared using filter aided sample preparation, either label free (Sample set 1) or with dimethyl labelling (Sample set 2), followed by Orbitrap-LC-MS/MS for protein analysis. The results showed that the milk serum protein was very constant in mid lactation (Sample set 1). Sample set 2 showed significant variation in the milk serum proteins between individual cows. The most variable proteins were immune-related proteins, whereas proteins related to nutrient synthesis and transport were relatively constant.

本观察性研究旨在探究奶牛乳汁血清蛋白质组的个体间与个体内差异。为解析乳汁血清蛋白质组的个体变异特征，本研究采用两套样本集开展相关研究。样本集1为成熟乳，在泌乳启动后2个月至泌乳结束前2个月的时间区间内采集了5个时间点的样本，同时记录了各样本对应的日粮、体细胞计数（Somatic Cell Count, SCC）及胎次信息；样本集2包含17份成熟乳样本，其泌乳天数处于与样本集1一致的区间范围。所有样本均采用滤膜辅助样本制备（filter aided sample preparation）流程进行前处理，其中样本集1采用无标记定量方式，样本集2采用二甲基标记定量方式，随后通过轨道阱液相色谱-串联质谱（Orbitrap-LC-MS/MS）完成蛋白质组分析。研究结果表明，泌乳中期的乳汁血清蛋白质组整体稳定性较高（对应样本集1的结果）；样本集2则显示，不同个体奶牛的乳汁血清蛋白存在显著差异。其中变异程度最高的蛋白为免疫相关蛋白，而与营养合成及转运相关的蛋白则相对恒定。