Relationships among quarter milk leukocyte proportions and cow and quarter-level variables under different intramammary infection statuses

Abstract

The use of milk leukocyte differential (MLD) test has been proposed as a complement to somatic cell count (SCC) to assess the presence and the severity of intramammary infection. However, detailed information regarding the behavior of MLD under different physiological or pathological stages of the cow is nonexistent. The objective was to analyze the association between milk leukocyte proportions provided by a commercial automated MLD test and multiple cow and quarter-level variables. The study population consisted of 104 Holstein cows (32 primiparous and 72 multiparous) in one farm. Cows were categorized by days in milk as early (<50 DIM; n=29), middle (50–250 DIM; n=25), and late lactation (>250 DIM; n = 50). Milk from 416 quarters was collected and analyzed for lymphocytes (LYM), neutrophils (NEU), and macrophages (MAC) counts using an automated milk fluorescence microscopy system. Concurrently, a sterile composite milk sample was collected from each cow for pathogen identification through microbiological culture. Culture results were classified as no growth (NOG), gram-negative (GN), gram-positive (GP), or other (OTH). Milk leukocyte proportions varied depending on the level of total leukocyte counts (TLC; P < 0.001). Similarly, leukocyte ratios (NEU:LYM, NEU:MAC, and phagocyte:LYM) were different for multiple TLC categories (P < 0.05). There was no association between parity number and MLD; however, cows in early lactation had the greatest proportions of NEU and LYM. Leukocyte ratios varied depending on parity number and stage of lactation. Cows in the medium milk-yield category had the smallest proportions of NEU and LYM, and there was significant variation in leukocyte ratios, depending on the level of milk yield. In healthy quarters, MLD were not associated with quarter position; however, the NEU:MAC ratio was greater in rear quarters than in front quarters. In quarters with TLC >100,000, NEU% was greater in rear quarters than in front quarters (P = 0.03). For quarters with pathogen growth, TLC was greatest for GN followed by OTH and GP (P < 0.001). Milk LD depended on the isolated pathogen group, although the magnitudes of the differences were small. Although the changes in the proportions of leukocytes in milk were associated with categories of TLC, levels of milk yield, and mastitis-causing pathogen groups, the deviations were small in magnitude. Additional research is necessary to determine the potential applications for this methodology.

Microscopic differential cell count and specific mastitis pathogens in cow milk from compost-bedded pack barns and cubicle barns

“…The proportions of leukocytes in healthy quarters were highly variable in different studies and in different environments (Paudyal et al, 2018). As reported by Yang et al (1997) and Paudyal et al (2018), fractions for macrophages and lymphocytes strongly depended on the lactation stage, but as shown in our present study, response pattern can differ between compost and cubicle. Also, the proportion of lymphocytes changed during lactation.…”

“…In contrast, macrophages were the predominant cell fraction in conventional farming systems in the study by Riollet et al (2001). The proportions of leukocytes in healthy quarters were highly variable in different studies and in different environments (Paudyal et al, 2018). As reported by Yang et al (1997) and Paudyal et al (2018), fractions for macrophages and lymphocytes strongly depended on the lactation stage, but as shown in our present study, response pattern can differ between compost and cubicle.…”

Factors Affecting the Patterns of Total Amount and Proportions of Leukocytes in Bovine Milk

“…These data suggest that in this group, the presence of high SCC as lactation proceeds is associated with a progressive increase in the number of macrophages. An increase in the proportion of macrophages in late lactations have been reported in previous studies on quarter milk samples [ 17 , 35 ], but these studies involved both healthy cows and with subclinical mastitis. In our study, reduction in the proportion and correspondent increase in overall number of macrophages was observed only in cows with a clear inflammatory process; these results may be related to the increase frequency of chronic mastitis in late lactation [ 36 , 37 ].…”

A Comparative Study on Changes in Total and Differential Milk Cell Counts, Activity, and Expression of Milk Phagocytes of Healthy and Mastitic Indigenous Sahiwal Cows

“…DLC indicates the percentage of individual cell populations such as neutrophils, macrophages, and lymphocytes, which play critical roles during intramammary infection ( 39 ). Usually, healthy udder comprises predominantly macrophages, whereas elevated neutrophil percentage is characteristic of the infected udder ( 15 , 38 ).…”

“…Moreover, the proportions of various white cells in milk can give a deep insight into the severity and stage of mammary infection (12)(13)(14). Besides, the fluctuations in the proportions of various immune cells of milk during mammary infection may indicate an infection with specific groups of microbes and reflect the potential of mammary immune response (15)(16)(17)(18). Milk phagocytes (neutrophils and macrophages) are the primary immune cells present in milk and represent the innate arm of mammary immune response during mammary infection (19,20).…”