Syrstad O, Røn I
Nord Vet Med. 1978 Apr-May;30(4-5):192-8.
The article presents results from two series of milk samples where samples from individual cows were collected at each milking over a period of two weeks. Fat content, protein content and cell count were determined for each sample. The cell counts (in thousands per ml) were transformed to logaritmic values and statistically analysed. As much as 75 to 80% of the variation (expressed as proportion of the total sums of squares) was due to differences "among cows" and about 3% due to differences "among days" during the sampling period. Samples from morning milkings had about 20% lower cell counts than samples from afternoon milkings. The standard deviation among samples from two consecutive milkings of the same cow (after removal of systematic differences between days and between morning and afternoon milkings) was computed as about 30% of the mean (i.e. coefficient of variation approximately 0.3). By combining samples from two milkings the random "error" in cell count can be reduced to about 20% of the mean. The samples exhibited a highly significant, but nummerically small, positive within-cow correlation between fat content and cell count, and between protein content and cell count, while the corresponding correlation between milk yield and cell count was slightly negative (non-significant).
本文展示了两组牛奶样本的结果，在为期两周的时间里，每次挤奶时采集每头奶牛的样本。测定每个样本的脂肪含量、蛋白质含量和细胞计数。细胞计数（每毫升数千个）转换为对数值并进行统计分析。高达75%至80%的变异（以总平方和的比例表示）是由于“奶牛之间”的差异，约3%是由于采样期间“天数之间”的差异。上午挤奶的样本细胞计数比下午挤奶的样本低约20%。同一头奶牛连续两次挤奶的样本（去除天数之间以及上午和下午挤奶之间的系统差异后）的标准差计算为平均值的约30%（即变异系数约为0.3）。通过合并两次挤奶的样本，细胞计数中的随机“误差”可降至平均值的约20%。样本显示，脂肪含量与细胞计数之间以及蛋白质含量与细胞计数之间存在高度显著但数值较小的正的奶牛内相关性，而产奶量与细胞计数之间的相应相关性略呈负相关（不显著）。
