Daryna Kurban

Intramammary infections are often associated with elevated SCC, a key indicator of udder inflammation and milk quality. This condition leads to substantial economic losses, primarily through its direct impact on milk production. In addition to reducing milk yield, IMI can negatively affect milk components such as fat, protein, and lactose. Consequently, the main objective of this longitudinal study was to estimate the association of IMI caused by these microorganisms on the SCS, milk yield (kg/d), and milk components at the quarter level. A secondary objective was to describe the quarter-level incidence and elimination rates of IMI caused by microorganisms other than Staphylococcus spp. A convenience sample of 5 dairy herds using an automated milking system was selected and visited every 2 wk for milk sample collection. Daily quarter milk yield data were extracted from the automatic milking system software. The determination of SCC and milk composition parameters was performed by Lactanet. Bacteriological culture was performed according to the National Mastitis Council guidelines. The different types of colonies were counted and identified using MALDI-TOF. For the first objective, we used generalized linear models with robust variance to estimate the incidence rate and elimination rate of IMI. For the second objective, 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 the test-day SCS, milk yield, lactose, protein, or fat as the outcome. The most prevalent non-Staphylococcus microorganisms in primiparous cows were Aerococcus viridans, Streptococcus dysgalactiae, and Corynebacterium bovis with mean prevalences (95% CI) of 3.8% (3.3%, 4.4%), 0.9% (0.7%, 1.3%), and 0.9% (0.7%, 1.2%), respectively. Similarly, for multiparous cows, the 3 most prevalent pathogens were C. bovis, A. viridans, and S. dysgalactiae, with mean prevalences (95% CI) of 5.2% (4.8%, 5.5%), 3.7% (3.4%, 4.0%), and 2.8% (2.5%, 3.1%), respectively. For both primiparous and multiparous cows, the incidence rate of S. dysgalactiae was low, at 0.1 and 0.2 new intramammary infections/100 quarter-weeks, respectively. However, quarters infected with S. dysgalactiae exhibited a lower elimination rate compared with infections caused by other microorganisms. A similar pattern was observed for S. uberis infections in multiparous cows. In primiparous cows, quarters infected by S. dysgalactiae produced 1.3 kg/d less compared with healthy quarters. In multiparous cows, milk yield was not significantly associated with IMI status; however, quarters infected with S. dysgalactiae produced 0.7 kg/d less than healthy quarters, though this difference was only numerical. Regarding milk composition, quarters infected by S. dysgalactiae in primiparous cows had a 0.2% reduction in lactose content, with no significant differences observed for protein or fat content. In multiparous cows, S. uberis infections resulted in a 1.0% reduction in fat content, whereas S. dysgalactiae infections led to a 0.2% reduction in lactose content. Intramammary infections caused by S. dysgalactiae had a moderate impact on milk yield, particularly in primiparous cows. Although the effects on milk composition were minimal, the reductions in milk production underscore the importance of managing infections to mitigate economic losses in dairy herds.

On Canadian dairy farms, staphylococcal species, including Staphylococcus aureus and NAS, cause most IMI in lactating cows. However, knowledge remains limited about their impact on quarter-level SCS, milk yield, and composition, as well as their lactational incidence and elimination rates. This study aimed to describe staphylococcal species-specific IMI association with SCS, milk production, and milk composition in primiparous and multiparous cows, and to describe their prevalence, incidence, and elimination rates. Five commercial dairy farms with automated milking systems in Québec, Canada, were visited biweekly to collect aseptic quarter milk samples. Cows were recruited at 3 to 14 DIM and sampled every other week until 305 DIM. Bacteriological culture and MALDI-TOF MS were used for staphylococcal identification. A total of 21,467 samples from 1,537 quarters of 387 cows (307 multiparous, 80 primiparous) were analyzed. The most prevalent staphylococci in mammary gland quarters were Staphylococcus chromogenes (4.0%), Staphylococcus epidermidis (2.6%), Staphylococcus haemolyticus (2.1%), and S. aureus (1.9%). Staphylococcus auricularis, Staphylococcus chromogenes, and Staphylococcus equorum IMI were more frequent in primiparous cows, whereas S. aureus, Staphylococcus epidermidis, and S. haemolyticus were more common in multiparous cows. Staphylococcus haemolyticus and S. epidermidis showed the highest incidence, whereas S. chromogenes and Staphylococcus simulans had elimination rates similar to or lower than S. aureus. Many lactational staphylococcal IMI were transient, with high species-specific elimination rates. Associations with quarter-level SCS, milk yield, and milk components were evaluated using 7,703 to 9,967 test-day samples from over 1,300 quarters of 369 cows. In primiparous cows, quarters with IMI by S. aureus, S. chromogenes, S. epidermidis, or S. simulans had higher SCS than healthy quarters. In multiparous cows, SCS was elevated in quarters infected by S. aureus, S. chromogenes, S. epidermidis, S. haemolyticus, S. simulans, or Staphylococcus xylosus. Milk yields in primiparous cows were generally unaffected by IMI status, whereas in multiparous cows, only S. aureus IMI reduced milk yield (7.9 vs. 10.2 kg/d in healthy quarters). No changes in milk fat were detected. Protein content was higher in S. aureus IMI quarters of multiparous cows. Lactose reductions occurred in primiparous cows' quarters with S. chromogenes or S. simulans IMI, and in multiparous cows' quarters with S. aureus, S. epidermidis, or S. simulans IMI. In conclusion, in primiparous cows, IMI by S. aureus, S. chromogenes, S. epidermidis, and S. simulans increased SCS, with S. simulans also reducing lactose, but no changes in milk yield, fat, or protein. In multiparous cows, higher SCS occurred with several staphylococcal species, milk yield was reduced only with S. aureus IMI, and lactose was reduced in quarters infected by S. aureus, S. epidermidis, and S. simulans.

Staphylococcal species are frequently isolated from dairy cows milk and are a very common cause of intramammary infections (IMI). First lactation cows may already have an IMI at calving, and these may be acquired during different stages of their development. Moreover, the dry period is another critical "nonlactating" period regarding the acquisition of new IMI, and these may persist until calving. The first objectives of this observational longitudinal cohort study were to: describe staphylococcal species-level IMI prevalence at calving in quarters from primiparous cows; describe staphylococcal species-level IMI prevalence before dry-off and following calving; and report the species-level incidence and persistence of staphylococcal IMI over the dry period in quarters from multiparous cows. A second objective was to report the species-level effect of early lactation staphylococcal IMI on the following lactation milk production and SCS in quarters from primiparous and multiparous cows. Quarter-milk samples were collected from each recruited cow on 5 dairy farms using automated milking systems (AMS; QC, Canada). First lactation cows were sampled 2 times between 3 and 14 DIM. Older cows were sampled 2 times, around 28 and 14 d before dry-off, and 2 times after calving, ∼3 and 14 DIM. Staphylococcal species were identified in milk samples using bacteriological culture followed by MALDI-TOF MS. Quarter-milk samples were collected for SCC measurements biweekly up to 305 DIM, and daily quarter-milk production was extracted from the AMS software up to 305 DIM. To estimate staphylococcal IMI dynamics, results for 301 quarters of 76 first lactation cows at calving and 1,750 quarters of 447 cows before dry-off and after calving were available. First lactation cows had a higher prevalence of staphylococcal IMI at calving than multiparous cows. In first lactation cows, the most prevalent staphylococcal IMI in early lactation was Staphylococcus chromogenes IMI (10.3%, 95% CI: 4.4%-21.9%), which was leading to substantial elevation of SCS (mean SCS of 3.9, 95% CI: 3.1%-4.6%) during the following lactation in comparison to healthy quarters (1.7, 95% CI: 1.2%-2.3%). However, quarter-level milk production was not affected by S. chromogenes IMI in primiparous cows. Staphylococcus aureus, Staphylococcus xylosus, Staphylococcus chromogenes, Staphylococcus simulans, Staphylococcus epidermidis, and Staphylococcus haemolyticus were able to persist throughout the dry period, although persistency rates varied by staphylococcal species. Acquisition of new staphylococcal IMI was also observed during the dry period. Finally, postcalving IMI by S. aureus, S. simulans, S. epidermidis, S. chromogenes, S. xylosus, and S. haemolyticus were all associated with higher quarter SCS in the subsequent lactation. Postcalving IMI by S. aureus and S. epidermidis were associated with quarter-milk yield reduction during the following lactation with losses of 1.9 kg/quarter-d (95% CI: 0.1%-3.7%), and of 1.7 kg/quarter-d (95% CI: 0.2%-3.2%), respectively. Although many NAS IMI were relatively frequent at calving in first lactation and older cows, could persist throughout the dry period and were associated with a measurable inflammation during the following lactation, few NAS species were actually associated with a measurable milk yield reduction.

Mastitis is the most common disease affecting dairy cattle and is associated with substantial milk loss. Somatic cell count (SCC) has been widely used as an indicator of udder inflammation (e.g., subclinical mastitis). More recently, differential somatic cell count (DSCC) has become available as an auxiliary tool for milk quality control, with the potential to indicate different stages of inflammation when combined with SCC. This paper aimed to investigate the association of somatic cell score (SCS) and DSCC with milk yield and milk components at the quarter-level. A convenience sample of 5 dairy herds using an automated milking system (AMS) was selected and visited every other week for milk sample collection. Fat, protein, and lactose content were analyzed at Lactanet (Canadian Network for Dairy Excellence, Sainte-Anne-de-Bellevue, Quebec, Canada) by mid-infrared spectroscopy using a MilkoScan FT6000. Determination of SCC and DSCC was also performed by Lactanet using a CombiFoss 7 DC instrument. Milk yield data was retrieved from the AMS. Given the hierarchical structure of the data, a linear mixed model was built with either milk yield or milk components as the outcomes. The results showed that elevated somatic cell score (SCS), in combination with lower proportions of DSCC, was associated with the highest milk loss for primiparous and multiparous cows. For instance, the estimated milk loss for a quarter with a SCS of 7 and a DSCC of 55% was 1.45 kg/d compared with a quarter with a SCS of 2 and DSCC of 65% in multiparous cows. The association was similar when the outcome was the lactose content. Quarters with elevated SCS and lower DSCC had the lowest lactose percentage. No significant changes in fat content were observed across different SCS levels in multiparous cows, and quarters with higher DSCC had the lowest fat percentage in primiparous and multiparous cows. Protein content tended to be lower in quarters with increased SCS and low DSCC. In quarters from primiparous cows with DSCC levels above 70%, protein content showed slight variation across SCS levels. For multiparous cows, however, protein content remained relatively stable across different SCS and DSCC levels. In conclusion, our findings revealed that the combination of elevated SCS and low DSCC was associated with the most substantial milk loss. These results could be used to optimize udder health management.

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 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 weeks 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 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 S. chromogenes, S. dysgalactiae, S. aureus, S. epidermidis, "other major," and "other minor," had an increase in DSCC by approximately 10.2%, 9.9%, 9.8%, 9.2%, 6.0%, and 4.9% 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.

Mastitis poses significant economic challenges for dairy farms. Therefore, enhancing the accuracy of diagnostic methods for detecting intramammary infections (IMI) can potentially improve prevention, control and treatment strategies. The somatic cell count (SCC) is a well-established parameter for identifying inflammation resulting from IMI. Given the recent introduction of differential somatic cell count (DSCC) for routine milk sample screening, limited research has been conducted to assess its additional benefits for diagnosing IMI. Therefore, our main objective was to evaluate the diagnostic accuracy of SCC, DSCC and SCC-DSCC combinations in detecting IMI caused by any pathogen or by major pathogens using quarter milk samples. Five dairy herds using automated milking systems were selected using convenience sampling in Québec, Canada. Determination of SCC and DSCC was performed by Lactanet (Ste-Anne de Bellevue, QC, Canada) using a CombiFoss 7 DC instrument. A 5-populations 2-tests Bayesian latent class models was used, with bacteriological culture employed as the imperfect reference test. Posterior estimates for sensitivity (Se), specificity (Sp), and the predictive values for 2 hypotheticals IMI prevalences due to any pathogen or major pathogens were computed. The proportion of quarters positive for any pathogen or major pathogen using milk culture was 31.7% (5,125/16,176) and 5.4% (871/16,176), respectively. For the detection of IMI by any pathogen, using a serial interpretation for the combination of SCC ≥100,000 and DSCC at ≥65% increased the Sp from 0.71 (95BCI: 0.70, 0.72) to 0.84 (95BCI: 0.83, 0.86) compared with SCC alone at the cut-off ≥100,000 cells/mL, although resulting in a slight decrease in Se from 0.49 (95BCI: 0.43, 0.54) to 0.46 (95BCI: 0.42, 0.50). Moreover, for detecting IMI caused by major pathogens, combining SCC at the threshold of ≥100,000 cells/mL and DSCC at the threshold of ≥65% using serial interpretation increased the Sp from 0.68 (95BCI: 0.67, 0.69) to 0.80 (95BCI: 0.79, 0.81) compared with SCC alone at the ≥100,000 cells/mL threshold. Our findings suggest that DSCC could be combined with SCC to provide a modest improvement in Sp with minimal compromise in Se for identifying IMI caused by any or by major pathogens. In addition, DSCC combined with SCC provided a small improvement in Se for detecting any pathogen using the parallel interpretation. However, no improvements in Se were observed when using the combination of SCC and DSCC for detecting major pathogens.

Mastitis, an inflammation of the udder primarily caused by an intramammary infection, is one of the most common diseases in dairy cattle. Somatic cell count (SCC) has been widely used as an indicator of udder inflammation, assisting in the detection of subclinical mastitis. More recently, differential somatic cell count (DSCC), which represents the combined proportion of lymphocytes and polymorphonuclear leukocytes, has become available for routine dairy milk screening, though it was not yet widely studied. Therefore, the objective of this study was to assess and compare the usefulness of quarter-level somatic cell score (SCS) or DSCC to predict the probability of subclinical mastitis. Additionally, our goals included estimating the sensitivity (Se) and specificity (Sp) of SCS and DSCC across all potential cut-off values. The current study was an observational study conducted on commercial dairy farms. Five dairy herds were selected using a convenience sampling. A Gaussian finite mixture model (GFMM) was applied to investigate the latent quarter subclinical mastitis status with either measurement, i.e., SCS or DSCC. Posterior values for SCS and DSCC obtained from the GFMM were used for predictive estimation of the parameters. The estimated SCS distribution for healthy quarters had a mean (standard deviation) of 1.4 (1.3), while, for quarters with subclinical mastitis, it was 4.5 (2.4). For DSCC, the estimated mean was 55.6% (15.2) for healthy quarters, whereas it was 80.4% (6.4) for quarters with subclinical mastitis. The most discriminant cut-off for SCS, as indicated by the Youden index, was 3.0, corresponding to exactly 100,000 cells/mL. At this threshold, the Se and Sp of SCS were 0.73 (95% Bayesian Credible Interval [BCI]: 0.70-0.77) and 0.90 (95% BCI: 0.89-0.91), respectively. The most discriminant cut-off point for DSCC was 70.0%, with corresponding the Se and Sp values of 0.95 (0.93, 0.96) and 0.83 (0.81, 0.85), respectively. For the SCS analysis, we obtained predictive probabilities of subclinical mastitis approaching 0 and 100%, with only a narrow range of SCS results yielding intermediate probabilities. On the other hand, predictive probabilities ranging from 0 to 90% were obtained for DSCC analysis, with a large range of DSCC results presenting intermediate probabilities. Thus, SCS seemed to surpass DSCC for predicting subclinical mastitis. These findings provided a foundation for future studies to further explore and validate the efficacy of GFMM for diagnostic tests yielding quantitative results.

Several studies have described variations in lactose content (LC) in dairy cows during udder quarter health disorder or negative energy balance (NEB). However, their joint effects on LC have never been described. This was the aim of a longitudinal observational study performed on 5 Quebec dairy farms using automatic milking systems. Quarter milk samples were collected every 14 d from 5 to 300 DIM. Quarter health status was described by combining SCC level (SCC^- or SCC⁺: < or ≥100,000 cells/mL, respectively) and infectious status (Patho^- or Patho⁺: absence or presence of pathogens on a milk culture, respectively). Cows with NEB in early lactation (DIM + quarters was lower (-0.17 ± 0.013 percentage points) compared with LC of SCC^- quarters for both primiparous and multiparous cows. Of the 162 bacterial species identified, only 8 species had a prevalence greater than 4.0%, and just 5 of them were associated with a reduction in LC: Staphylococcus aureus, Staphylococcus chromogenes, Streptococcus dysgalactiae, Staphylococcus epidermidis, and Staphylococcus simulans. Cows identified as BHB+ and BHB++ in early lactation had a lower LC (-0.05 ± 0.019 and -0.13 ± 0.020 percentage points, respectively) compared with BHB- cows. For BHB++ cows, in both parity groups the decrease in LC (-0.20 ± 0.025 percentage points) was higher in SCC⁺ quarters compared with SCC^- quarters. Moreover, the additive effect of the quarter health status and NEB on milk LC was greater with larger increases in BHB. Our findings highlight the necessity to jointly take into consideration both quarter health status and milk BHB concentration when using LC as a biomarker for NEB.

Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry provides accurate species-level identification of many, microorganisms retrieved from bovine milk samples. However, not all those microorganisms are pathogenic. Our study aimed to: (1) determine the species-specific prevalence of microorganisms identified in bovine milk of apparently healthy lactating quarters vs. quarters with clinical mastitis (CM); and (2) map current information and knowledge gaps on udder health relevance of microorganisms retrieved from bovine milk samples. A mixed study design (meta-analysis and mapping review) was chosen. We gathered several large Canadian, US and Brazilian data sets of MALDI-TOF results for organisms cultured from quarter milk samples. For meta-analysis, two datasets (apparently healthy quarters vs. CM samples) were organized. A series of meta-analyses was conducted to determine microorganisms’ prevalence. Then, each species reported was searched through PubMed to investigate whether inflammation (increased somatic cell count (SCC) or signs of CM) was associated with microorganism’s recovery from milk. A total of 294 different species of microorganisms recovered from milk samples were identified. Among 50,429 quarter-milk samples from apparently healthy quarters, the 5 most frequent species were Staphylococcus chromogenes (6.7%, 95% CI 4.5–9.2%), Aerococcus viridans (1.6%, 95% CI 0.4–3.5%), Staphylococcus aureus (1.5%, 95% CI 0.5–2.8%), Staphylococcus haemolyticus (0.9%, 95% CI 0.4–1.5%), and Staphylococcus epidermidis (0.7%, 95% CI 0.2–1.6%). Among the 43,924 quarter-milk CM samples, the 5 most frequent species were Escherichia coli (11%, 95% CI 8.1–14.3%), Streptococcus uberis (8.5%, 95% CI 5.3–12.2%), Streptococcus dysgalactiae (7.8%, 95% CI 4.9–11.5%), Staphylococcus aureus (7.8%, 95% CI 4.4–11.9%), and Klebsiella pneumoniae (5.6%, 95% CI 3.4–8.2%). When conducting the PubMed literature search, there were 206 species identified by MALDI-TOF for which we were not able to find any information regarding their association with CM or SCC. Some of them, however, were frequently isolated in our multi-country dataset from the milk of quarters with CM (e.g., Citrobacter koseri, Enterococcus saccharolyticus, Streptococcus gallolyticus). Our study provides guidance to veterinarians for interpretation of milk bacteriology results obtained using MALDI-TOF and identifies knowledge gaps for future research.

Milk production may be reduced before dry-off to decrease the risk of cows developing intramammary infections during the dry period. Such reductions in milk may be possible in automated milking systems (AMS) where milking frequency and feed allocation at the AMS can be controlled at the cow level. This study investigated the effect of dry-off management of cows milked in AMS on milk yield, milking behavior, and somatic cell count (SCC). Using a 2 × 2 factorial arrangement of treatments, applied from d 14 to 1 before dry-off, 445 cows from 5 commercial dairy farms in Quebec, Canada, were assigned within farm to either (1) reduced feed [RF; allowed a maximum of 0.75 kg/d of AMS pellet for the first week (14 to 8 d before dry-off) of treatment, and 0.50 kg/d for the second week (7 to 1 d before dry-off) of treatment], or (2) nonreduced feed (NF; allowed up to 2 kg/d of AMS pellet), and either (1) reduced milking (RM; reduced to 2 milkings/d or as many times as required to yield 17 kg/milking), or (2) nonreduced milking (NM; allowed up to 6 AMS milkings/d) and no maximum production. Feed and milking behavior data, as well as milk yield and SCC were collected from the AMS software. The RF cows had lower AMS feed delivered during the treatment period, as per the experimental design. Across the treatment period, the NF-NM cows had the highest milking frequency (2.7 times/d), followed by the RF-NM cows (2.4 times/d), and then both of the RM groups (1.8 times/d), which did not differ from each other. All cows, except the NF-NM cows, were gradually milked less frequently as dry-off approached. Across the entire 2-wk treatment period before dry-off, cows with RM allowance experienced a higher reduction in milk yield compared with the cows with no milking allowance restrictions (-4.8 vs. -3.6 kg). Similarly, cows with a RF allocation tended to have a higher reduction in milk yield than cows with NF (-4.6 vs. -3.7 kg). As result, those cows with both reduced milking permissions and feed allocation at the AMS experienced the greatest drop in milk production before dry-off. There were no differences between treatments for milking frequency or yield in the next lactation. Somatic cell score (calculated from SCC) was not different between treatments in the 2-wk or day before dry-off, nor in the first month after calving. Overall, these data suggest that reducing both milking frequency and feed quantity in the AMS is the most efficient method to decrease milk yield before dry-off, without negatively influencing milking frequency or yield in the next lactation, as well as without affecting milk quality.