Fonseca Mariana, Kurban Daryna, Roy Jean-Philippe, Santschi Débora E, Molgat Elouise, Dufour Simon
Department of Pathology and Microbiology, Faculty of Veterinary Medicine, Université de Montréal, Saint-Hyacinthe, QC J2S2M2, Canada; Regroupement FRQNT Op+lait, Saint-Hyacinthe, QC J2S2M2, Canada.
Regroupement FRQNT Op+lait, Saint-Hyacinthe, QC J2S2M2, Canada; Department of Clinical Sciences, Faculty of Veterinary Medicine, Université de Montréal, Saint-Hyacinthe, QC J2S2M2, Canada.
J Dairy Sci. 2025 Apr;108(4):3878-3899. doi: 10.3168/jds.2024-25401. Epub 2024 Dec 17.
Microbial infections of the mammary gland often cause mastitis, and it can lead to substantial economic losses within the dairy industry due to its direct negative impact on milk production and composition and the associated treatment costs. Somatic cell count has emerged as a critical indicator in monitoring udder health, and recently, the large-scale availability of differential cell count analysis potentially offers new insights into underlying physiological processes. Therefore, the main objective of this study was to estimate the variation of differential SCC (DSCC) and SCC of individual quarter-level milk samples of cows according to (1) their intramammary infectious status; (2) parity of the cow; (3) quarter location; and (4) DIM at the time of sampling. A convenience sample of 5 dairy herds using an automated milking system was selected and visited every 2 wk for milk sample collection. The determination of SCC and DSCC was performed by Lactanet using a CombiFoss 7 DC instrument. The bacteriological culture was performed according to the National Mastitis Council standards. The different types of colonies (up to 10 colonies) were counted and identified using MALDI-TOF. Given the hierarchical structure of the data, a 4-level, linear mixed model with herd, cow, and quarter as random intercepts was built with either SCS or DSCC as the outcome. Differential SCC varied broadly in the SCS range 2 to 12 but tended to have a narrower variation at higher SCS levels. The effect of DIM on DSCC depended on the parity. Early in lactation, primiparous cows tended to have lower DSCC than older cows. Following 230 DIM, the DSCC in primiparous exhibited an upward trend, whereas, in older cows, it tended to decline. The quarter position did not affect either DSCC or SCS. Quarters infected with Staphylococcus chromogenes, Streptococcus dysgalactiae, Staphylococcus aureus, Staphylococcus epidermidis, "other major," and "other minor," had an increase in DSCC by ∼10.2%, 9.9%, 9.8%, 9.2%, 6.0%, and 4.9%, respectively, when compared with quarters with no growth. Our findings highlighted that IMI, parity, and DIM influenced DSCC. Therefore, these parameters should be considered when interpreting DSCC.
乳腺的微生物感染常引发乳腺炎，因其对牛奶产量和成分产生直接负面影响以及相关治疗成本，会给乳制品行业造成巨大经济损失。体细胞计数已成为监测乳房健康的关键指标，近来，差异细胞计数分析的大规模应用有望为潜在的生理过程提供新见解。因此，本研究的主要目的是根据以下因素估计奶牛个体季度水平牛奶样本的差异体细胞计数（DSCC）和体细胞计数（SCC）的变化：（1）其乳房内感染状况；（2）奶牛胎次；（3）乳腺位置；（4）采样时的泌乳天数（DIM）。选取了5个使用自动挤奶系统的奶牛场的便利样本，每2周走访一次以采集牛奶样本。SCC和DSCC的测定由Lactanet公司使用CombiFoss 7 DC仪器进行。细菌培养按照美国国家乳腺炎委员会标准进行。使用基质辅助激光解吸电离飞行时间质谱（MALDI - TOF）对不同类型的菌落（最多10个菌落）进行计数和鉴定。鉴于数据的层次结构，构建了一个以畜群、奶牛和乳腺为随机截距的四级线性混合模型，以体细胞评分（SCS）或DSCC作为结果变量。在SCS范围为2至12时，差异体细胞计数变化幅度较大，但在较高SCS水平时变化幅度趋于变窄。DIM对DSCC的影响取决于胎次。泌乳早期，初产奶牛的DSCC往往低于经产奶牛。在230天泌乳期之后，初产奶牛的DSCC呈上升趋势，而经产奶牛的DSCC则趋于下降。乳腺位置对DSCC或SCS均无影响。与未生长菌落的乳腺相比，感染产色葡萄球菌、乳房链球菌、金黄色葡萄球菌、表皮葡萄球菌、“其他主要菌”和“其他次要菌”的乳腺，其DSCC分别增加了约10.2%、9.9%、9.8%、9.2%、6.0%和4.9%。我们的研究结果突出表明，乳房内感染（IMI）、胎次和DIM会影响DSCC。因此，在解释DSCC时应考虑这些参数。
