Bacterial spore levels in bulk tank raw milk are influenced by environmental and cow hygiene factors

Sporeforming bacteria are responsible for the spoilage of several dairy products including fluid milk, cheese, and products manufactured using dried dairy powders as ingredients. Sporeforming bacteria represent a considerable challenge for the dairy industry because they primarily enter the dairy product continuum at the farm, survive processing hurdles, and subsequently grow in finished products. As such, strategies to reduce spoilage due to this group of bacterial contaminants have focused on understanding the effect of farm level factors on the presence of spores in bulk tank raw milk with the goal of reducing spore levels in raw milk, as well as understanding processing contributions to spore levels and outgrowth in finished products. The goal of the current study was to investigate sources of spores in the farm environment and survey farm management practices to identify variables using multimodel inference, a model averaging approach that eliminates the uncertainty of traditional model selection approaches, that affect the presence and levels of spores in bulk tank raw milk. To this end, environmental samples including feed, bedding, manure, soil, water, and so on, and bulk tank raw milk were collected twice from 17 upstate New York dairy farms over a 19-mo period and the presence and levels of various spore types (e.g., psychrotolerant, mesophilic, thermophilic, highly heat resistant thermophilic, specially thermoresistant thermophilic, and anaerobic butyric acid bacteria) were assessed. Manure had the highest level of spores for 4 out of 5 aerobic spore types with mean counts of 5.87, 5.22, 4.35, and 3.68 log cfu/g of mesophilic, thermophilic, highly heat resistant thermophilic, and specially thermoresistant thermophilic spores, respectively. In contrast, bulk tank raw milk had mean spore levels below 1 log cfu/mL across spore types. Multimodel inference was used to determine variables (i.e., management factors, environmental spore levels, and meteorological data from each sampling) that were important for presence or levels of each spore type in bulk tank raw milk. Analyses indicated that variables of importance for more than one spore type included the residual level of spores in milk from individual cows after thorough teat cleaning and forestripping, udder hygiene, clipping or flaming of udders, spore level in feed commodities, spore level in parlor air, how often bedding was topped up or changed, the use of recycled manure bedding, and the use of sawdust bedding. These results improve our understanding of how spores transfer from environmental sources into bulk tank raw milk and provide information that can be used to design intervention trials aimed at reducing spore levels in raw milk.     

A survey of foodborne pathogens in bulk tank milk and raw milk consumption among farm families in pennsylvania

A 2-part study was conducted to determine the risk of exposure to human pathogens from raw milk. The first part of the study focused on determining raw milk consumption habits of dairy producers. A total of 248 dairy producers from 16 counties in Pennsylvania were surveyed. Overall, 105 (42.3%) of the 248 dairy producers consumed raw milk and 170 (68.5%) of the 248 dairy producers were aware of foodborne pathogens in raw milk. Dairy producers who were not aware of foodborne pathogens in raw milk were 2-fold more likely to consume raw milk compared with dairy producers who were aware of foodborne pathogens. The majority of dairy producers who consumed raw milk indicated that taste (72%) and convenience (60%) were the primary factors for consuming raw milk. Dairy producers who resided on the dairy farm were nearly 3-fold more likely to consume raw milk compared with those who lived elsewhere. In the second part of the study, bulk tank milk from the 248 participating dairy herds was examined for foodborne pathogens. Campylobacter jejuni (2%), Shiga toxin-producing Escherichia coli (2.4%), Listeria monocytogenes (2.8%), Salmonella (6%), and Yersinia enterocolitica (1.2%) were detected in the milk samples. Salmonella isolates were identified as S. enterica serotype Typhimurium (n = 10) and S. enterica serotype Newport (n = 5). Of the 248 bulk tank milk samples, 32 (13%) contained ≥1 species of bacterial pathogens. The findings of the study could assist in developing farm community-based educational programs on the risks of consuming raw milk.     

Evaluation of bulk tank milk PCR and bulk tank milk modified ELISA tests for the detection of paratuberculosis at the herd level in goat and sheep dairies in Ontario,Canada

Early identification of dairy goat herds and dairy sheep flocks infected with Mycobacterium avium ssp. paratuberculosis is important for controlling this infection and minimizing economic losses. The objective of this study was to evaluate 2 bulk tank milk (BTM) paratuberculosis tests (PCR and modified ELISA) as potential herd-level tests. These tests were compared with the results obtained from testing 20 randomly selected lactating animals per farm (>2 yr) with an individual animal test (fecal culture, fecal PCR, serum ELISA, and milk ELISA). The study was conducted using 29 dairy goat herds and 21 dairy sheep flocks in Ontario, Canada, visited between October 2010 and August 2011. The sensitivity of the BTM PCR was poor in both the dairy goat herds (0.0%) and dairy sheep flocks (25.0%), but exhibited 100% specificity in both species. In comparison, the BTM modified ELISA demonstrated higher sensitivity. In goats, sensitivity ranged from 33.3 to 34.8% when fecal culture and PCR were the reference tests, respectively (specificities were both 100%), and 71.4 to 87.5% when the milk and serum ELISA, respectively, were the reference tests (specificities were 86.4 and 95.2%). The BTM modified ELISA in dairy sheep demonstrated comparable sensitivities, but lower specificities. When fecal culture and PCR were the reference test, sensitivities were 50.0 and 46.7%, respectively (specificities were 77.8 and 83.3%). The sensitivities when the milk and serum ELISA were the reference tests were 87.5 and 72.7%, respectively (specificities were 92.3 and 100%). Fecal PCR was the only individual animal test to identify significantly more farms as positive than the BTM PCR and modified ELISA test in both species. Therefore, whereas the BTM modified ELISA may provide an organization or control program with a high level of confidence that a BTM-positive farm is actually positive (high positive predictive value), if a producer wishes to increase the odds that a positive farm will test positive, so as not to miss an infection, then sampling and testing 20 animals with fecal PCR will better meet that objective.     

Effect of short-term versus long-term grassland management and seasonal variation in organic and conventional dairy farming on the composition of bulk tank milk

Bulk tank milk from 28 dairy farms was sampled every second month for 2 yr to assess the effects of grassland management, production system and season on milk fatty acid (FA) composition, concentrations of fat-soluble vitamins, Se, and milk sensory quality. Grassland management varied in terms of time since establishment. Short-term grassland management (SG) was defined as establishment or reseeding every fourth year or more often, and long-term grassland management (LG) was defined as less frequent establishment or reseeding. Fourteen organic (ORG) dairy farms with either short-term or long-term grassland management were paired with 14 conventional (CON) farms with respect to grassland management. Within ORG farms, SG farms differed from LG farms in herbage botanical composition, but not in concentrate FA concentrations, dry matter intake, or milk yield. Within CON farms, herbage composition, concentrate FA concentrations, dry matter intake, and milk yield showed no or insignificant variations. The ORG farms differed from CON farms in herbage botanical composition, concentrate FA concentrations, concentrate intake, and milk yield. Compared with ORG-LG farms, ORG-SG farms produced milk fat with higher proportions of C10:0 and C12:0 associated with higher herbage proportions of legumes (Fabaceae) and lower proportions of other dicotyledon families. Compared with milk from CON farms, milk fat from ORG farms had higher proportions of most saturated FA and all n-3 FA, but lower proportions of C18:0 and C18:1 cis-9 associated with higher forage proportion and differences in concentrations of FA in concentrates. Compared with the outdoor-feeding periods, the indoor feeding periods yielded milk fat with higher proportions of most short-chain and medium-chain FA and lower proportions of most C18-FA associated with grazing and higher forage proportions. Milk concentrations of α-tocopherol and β-carotene were lower during the grazing periods. Inclusion of fishmeal in organic concentrates may explain higher Se concentrations in organically produced milk. Milk sensory quality was not affected in this study. In conclusion, grassland management had minor effects on milk composition, and differences between ORG farms and CON farms may be explained by differences in concentrate intake and concentrate FA concentrations. Milk produced on ORG farms versus CON farms and milk produced during the outdoor versus indoor feeding periods had potential health benefits due to FA composition. In contrast, the higher milk-fat proportions of saturated FA in milk from ORG farms may be perceived as negative for human health.     

Graduate Student Literature Review: Current understanding of the influence of on-farm factors on bovine raw milk and its suitability for cheesemaking

Relationships between dairy farm practices, the composition and properties of raw milk, and the quality of the resulting cheese are complex. In this review, we assess the effect of farm factors on the quality of bovine raw milk intended for cheesemaking. The literature reports several prominent farm-related factors that are closely associated with milk quality characteristics. We describe their effects on the composition and technological properties of raw milk and on the quality of the resulting cheese. Cow breed, composite genotype, and protein polymorphism all have noticeable effects on milk coagulation, cheese yield, and cheese composition. Feed and feeding strategy, dietary supplementation, housing and milking system, and seasonality of milk production also influence the composition and properties of raw milk, and the resulting cheese. The microbiota in raw milk is influenced by on-farm factors and by the production environment, and may influence the technological properties of the milk and the sensory profile of certain cheese types. Advances in research dealing with the technological properties of raw milk have undoubtedly improved understanding of how on-farm factors affect milk quality attributes, and have refuted the concept of one milk for all purposes. The specific conditions for milk production should be considered when the milk is intended for the production of cheese with unique characteristics. The scientific identification of these conditions would improve the current understanding of the complex associations between raw milk quality and farm and management factors. Future research that considers dairy landscapes within broader perspectives and develops multidimensional approaches to control the quality of raw milk intended for long-ripening cheese production is recommended.     

Single-molecule real-time sequencing reveals differences in bacterial diversity in raw milk in different regions and seasons in China

The quality of raw milk is a key factor influencing the whole dairy processing chain. The richness and diversity of bacteria in raw milk affect its quality and safety. However, traditional microbial detection methods mainly depend on the known microbe culture and are often time consuming. Thus, the development of efficient ways for supervising any possible microbiological contamination is desiderated. In the current work, single-molecule real-time (SMRT) sequencing, developed by Pacific Biosciences (PacBio), was applied to acquire long reads and applied for discrimination of bacteria at species level. Forty samples of raw milk obtained from Beijing, Hebei, Inner Mongolia, Shanghai, and Guangdong in China during summer, autumn, and winter were investigated. Among 35 bacteria species identified in these samples, Acinetobacter albensis, Pseudomonas gessardii, Pseudomonas weihenstephanensis, and Rahnella inusitata were the bacteria with the highest relative abundance in the overall sample, whereas the bacteria with the highest relative abundance in raw milk samples of different origins and seasons are different. Significant differences in bacterial richness and bacterial community diversity in raw milk grouped according to different production areas and different sampling seasons were confirmed by Welch's t-test. Interestingly, the transport distance and transport time positively correlated with the relative abundance of Pseudomonas weihenstephanensis, suggesting that the content of this bacteria was expected to be a standard for evaluating the freshness of raw milk. Pathogens Bacillus cereus and Klebsiella pneumoniae were detected in most samples, indicating that the raw milk was at risk of contamination by pathogenic bacteria. Moreover, the findings of this study provide important evidence for quality and safety monitoring and biological control of raw milk.     

Relationships between fecal culture, ELISA, and bulk tank milk test results for Johne's disease in US dairy herds

Objectives were to estimate percentages of seropositive herds with cows shedding Mycobacterium paratuberculosis in feces and milk, and to estimate sensitivity, specificity, and predictive value of an ELISA relative to fecal culture. Dairy cows (n = 712) were randomly selected from 61 herds previously identified by ELISA as positive for Johne's disease. Fecal and bulk tank milk samples (n = 52 of 61 herds) were obtained from 10 states in the United States. Fecal samples were processed by a double centrifugation, double decontamination culture procedure. Milk samples were processed for both culture and DNA analysis by using polymerase chain reaction (PCR). Of 24 herds with at least three cows that had tested ELISA-positive, 79% were also culture-positive, compared with 18 of 37 herds with one or two ELISA-positive cows. Both fecal-culture and ELISA results were available on 651 cows; only 25% of cows that were fecal-culture positive also tested positive by ELISA and over 6% of cows that were fecal-culture negative tested ELISA-positive. Milk samples all cultured negative, but analysis of milk samples by PCR resulted in 68% of herds positive for M. paratuberculosis DNA including 24 of 31 herds with positive fecal cultures and 11 of 21 herds with negative fecal cultures. Sensitivity and specificity of the ELISA compared with fecal culture is lower than previously reported and perhaps best used in screening herds because of limited efficacy to predict infection in individual cows. In addition, contamination of bulk tank milk samples with M. paratuberculosis does occur in seropositive herds, even in some with negative fecal cultures.     

Aflatoxin M1 and ochratoxin A in raw bulk milk from French dairy herds

Mycotoxins in milk are a public health concern and have to be regularly monitored. A survey on the presence of aflatoxin M₁ (AFM₁) and ochratoxin A (OTA) in raw bulk milk was conducted in 2003 in the northwest of France, the main French milk-producing basin. Randomly selected farms (n = 132) were characterized by a diet based on corn silage and containing a large proportion of on-farm produced cereals, feeding sources that are frequently contaminated by mycotoxins. Farms were surveyed twice in winter and in summer. At each sampling time, a trained surveyor completed a questionnaire recording farm management procedures and production traits. The AFM₁ was found in 3 out of 264 samples but at levels (26 ng/L or less) that are below the European legislation limit of 50 ng/L. Traces of AFM₁ (less than 8 ng/L) were also found in 6 other samples. The OTA was detected in 3 samples also at low levels, 5 to 8 ng/L. Farms that tested positive to the presence of mycotoxins, 12 in total including 6 farms that had traces of AFM₁, differed from negative farms by a more extensive use of total mixed rations, 58 vs. 27%. In addition, the positive farms tended to have lower milk yields. Although the incidence of milk contamination with AFM₁ and OTA at the farm level was low during the period studied, production and management data from the surveyed farms suggest a link between feeding management practices and mycotoxin contamination.     

Both sampling seasonality and geographic origin contribute significantly to variations in raw milk microbiota,but sampling seasonality is the more determining factor

Accurately profiling and characterizing factors shaping raw milk microbiota would provide practical information for detecting microbial contamination and unusual changes in milk. The current work was an observational study aiming to profile the microbiota of raw milk collected across wide geographic regions in China in different seasons and to investigate the contribution of geographical, seasonal, and environmental factors in shaping the raw milk microbiota. A total of 355 raw cow milk samples from healthy Holsteins and 41 environmental samples (farm soil and surface of milking room floor) were collected from 5 dairy farms in 5 Chinese provinces (namely, Daqing in Heilongjiang province, Jiaozuo in Henan province, Qingyuan in Guangdong province, Suqian in Jiangsu province, and Yinchuan in Ningxia Hui Autonomous Region) in January, May, and September 2018. The microbial communities in raw milk and farm environmental samples were determined using the PacBio small-molecule real-time circular consensus sequencing, which generated high-fidelity microbiota profiles based on full-length 16S rRNA genes; such technology was advantageous in producing accurate species-level information. Our results showed that both seasonality and sampling region were significant factors influencing the milk microbiota; however, the raw milk microbiota was highly diverse according to seasonality, and sampling region was the less determining factor. The wide variation in raw milk microbial communities between samples made it difficult to define a representative species-level core milk microbiota. Nevertheless, 3 most universal milk-associated species were identified: Lactococcus lactis, Enhydrobacter aerosaccus, and Acinetobacter lwoffii, which were consistently detected in 99%, 95%, and 94% of all analyzed milk samples, respectively (n = 355). The top taxa accounting for the overall seasonal microbiota variation were Bacillus (Bacillus cereus, Bacillus flexus, Bacillus safensis), Lactococcus (Lactococcus lactis, Lactococcus piscium, Lactococcus raffinolactis), Lactobacillus (Lactobacillus helveticus, Lactobacillus delbrueckii), Lactiplantibacillus plantarum, Streptococcus agalactiae, Enhydrobacter aerosaccus, Pseudomonas fragi, and Psychrobacter cibarius. Unlike the milk microbiota, the environmental microbiota did not exhibit obvious pattern of seasonal or geographic variation. However, this study was limited by the relatively low number and types of environmental samples, making it statistically not meaningful to perform further correlation analysis between the milk and environmental microbiota. Nevertheless, this study generated novel information on raw milk microbiota across wide geographic regions of China and found that seasonality was more significant in shaping the raw milk microbiota compared with geographic origin     

Predictive modeling of Bacillus cereus spores in farm tank milk during grazing and housing periods

The shelf life of pasteurized dairy products depends partly on the concentration of Bacillus cereus spores in raw milk. Based on a translation of contamination pathways into chains of unit-operations, 2 simulation models were developed to quantitatively identify factors that have the greatest effect on the spore concentration in milk. In addition, the models can be used to determine the reduction in concentration that could be achieved via measures at the farm level. One model predicts the concentration when soil is the source of spores, most relevant during grazing of cows. The other model predicts the concentration when feed is the main source of spores, most relevant during housing of cows. It was estimated that when teats are contaminated with soil, 33% of the farm tank milk (FTM) contains more than 3 log₁₀ spores/L of milk. When feed is the main source, this is only 2%. Based on the predicted spore concentrations in FTM, we calculated that the average spore concentration in raw milk stored at the dairy processor during the grazing period is 3.5 log₁₀ spores/L of milk and during the housing period is 2.1 log₁₀ spores/L. It was estimated that during the grazing period a 99% reduction could be achieved if all farms minimize the soil contamination of teats and teat cleaning is optimized. During housing, reduction of the concentration by 60% should be feasible by ensuring spore concentrations in feed below 3 log₁₀ spores/g and a pH of the ration offered to the cows below 5. Implementation of these measures at the farm level ensures that the concentration of B. cereus spores in raw milk never exceeds 3 log₁₀ spores/L.     

Short communication: Informative value of an ELISA applied to bulk tank milk to assess within-herd prevalence of digital dermatitis in dairy herds

The objective of this study was to assess whether an antibody ELISA applied to bulk tank milk (BTM) could be used to accurately estimate within-herd prevalence of digital dermatitis (DD). The ELISA was designed for the detection of antibodies against Treponema phagedenis-like strain V1 (PrrA antigen). The hind feet of all lactating cows from 40 commercial French dairy herds with a history of DD were scored by an observer in the milking parlor, using the 4 M-stage system. After milking, a BTM sample was collected and tested for anti-Treponema phagedenis-like antibodies using the antibody ELISA. Within-herd DD prevalence at the cow level was determined using 2 different approaches: (1) having DD lesion on at least 1 hind foot (Prev; prevalence of affected cows), and (2) having an M1 or M2 lesion on at least 1 hind foot (PrevA; prevalence of cows affected by DD in an active stage). Receiver operating characteristic analysis was used to determine both optimal within-herd DD prevalence and BTM sample to positive (S/P) ratio cut-off values. Two optimal cut-off values were identified. Herds with an S/P ratio of BTM ≤0.2 had a Prev ≤10% (sensitivity = 0.97, specificity = 1), whereas herds with an S/P ratio of BTM >0.38 had a Prev >40% (sensitivity = 0.94, specificity = 0.86). In the same way but with a slightly lower specificity, an S/P ratio >0.38 corresponds also to a PrevA >18% (sensitivity = 0.92, specificity = 0.70). The BTM antibody ELISA shows great promise for screening purposes during DD management programs.     

西藏乳及发酵乳制品中乳酸菌与酵母菌分布

西藏当地牦牛乳及发酵乳制品中的微生物分布备受科研人员的关注,而且重点多集中在其中的乳酸菌和酵母菌。本文对西藏当地乳及乳制品中乳酸菌与酵母菌的分布做了详细的介绍,包括原料乳、曲拉和藏灵菇乳中的乳酸菌和酵母菌的研究现状,并对今后的发展趋势做了分析。      

Evaluation of test characteristics of 2 ELISA tests applied to bulk tank milk and claw-trimming records for herd-level diagnosis of bovine digital dermatitis using latent class analysis

Bovine digital dermatitis (DD) is an infectious claw disease with a negative effect on animal welfare and production. Treponema spp. is the main causative agent, and infected animals produce specific antibodies. Our aim was to estimate sensitivity (Se) and specificity (Sp) of 2 ELISA research tests, Medicago's ELISA test and GD Animal Health's in-house ELISA test, for detection of DD-associated Treponema antibodies in bulk tank milk. We used bulk tank milk samples from 154 Norwegian dairy cattle herds, 96 from an expected high-prevalence region and 58 from a low-prevalence region. Both tests were evaluated separately against herd-level (aggregated) claw-trimming records extracted from the Norwegian Dairy Herd Recording System using latent class models in a Bayesian analysis. Cutoff values were selected using an explorative approach, and both noninformative priors for all parameters and informative β priors for distribution of Se and Sp of claw trimming were explored. The estimated (median) true herd-level prevalence of digital dermatitis varied between 24 and 30% in the high-prevalence region and between 3 and 6% in the low-prevalence region. For Medicago's ELISA test, an Se (95% posterior credible interval) of 0.57 (0.32; 0.94) could be achieved without compromising Sp, and for GD Animal Health's in-house ELISA test, an Se of 0.60 (0.37; 0.92) was achieved. Our study showed that both ELISA tests can detect antibodies against DD-associated Treponema spp. in bulk tank milk. However, neither of the 2 ELISA tests produced satisfactory sensitivity without compromising specificity. Based on these results, inspection at claw trimming in a chute is necessary for surveillance and control of DD at the herd level in Norway, although these ELISA tests of bulk tank milk might be a useful supplement.     

Aerobic spore-forming bacteria in bulk raw milk: factors influencing the numbers of psychrotrophic, mesophilic and thermophilic Bacillus spores

Psychrotrophic, mesophilic and thermophilic spore concentrations of Bacillus spp. were determined on a weekly basis in bulk raw milk samples obtained from a central processing facility, over one calendar year. These data were correlated with concentrations of metal ions, free amino acids and somatic cell counts obtained from the same samples, as well as local meteorological mean temperature and relative humidity measurements relating to the same test period. A heat treatment of 80°C for 20 min followed by the addition of L-alanine to the milk at 0.1% w/v and incubation at 55°C for 7 days gave optimal recovery conditions for thermophilic spores. Free amino acids, metal ions, somatic cell counts, temperature, and relative humidity measurements were each significantly correlated with the recovery of spores of Bacillus spp. from bulk raw milk, although no single factor was shown to demonstrate a consistent effect with the psychrotrophic, mesophilic and thermophilic spore groups studied.     

Bedding and bedding management practices are associated with mesophilic and thermophilic spore levels in bulk tank raw milk

Mesophilic and thermophilic spore-forming bacteria represent a challenge to the dairy industry, as these bacteria are capable of surviving adverse conditions associated with processing and sanitation and eventually spoil dairy products. The dairy farm environment, including soil, manure, silage, and bedding, has been implicated as a source for spores in raw milk. High levels of spores have previously been isolated from bedding, and different bedding materials have been associated with spore levels in bulk tank (BT) raw milk; however, the effect of different bedding types, bedding management practices, and bedding spore levels on the variance of spore levels in BT raw milk has not been investigated. To this end, farm and bedding management surveys were administered and unused bedding, used bedding, and BT raw milk samples were collected from dairy farms (1 or 2 times per farm) across the United States over 1 yr; the final data set included 182 dairy farms in 18 states. Bedding suspensions and BT raw milk were spore pasteurized (80°C for 12 min), and mesophilic and thermophilic spores were enumerated. Piecewise structural equation modeling analysis was used to determine direct and indirect pathways of association among farm and bedding practices, levels of spores in unused and used bedding, and levels of spores in BT raw milk. Separate models were constructed for mesophilic and thermophilic spore levels. The analyses showed that bedding material had a direct influence on levels of spores in unused and used bedding as well as an indirect association with spore levels in BT raw milk through used bedding spore levels. Specific bedding and farm management practices as well as cow hygiene in the housing area were associated with mesophilic and thermophilic spore levels in unused bedding, used bedding, and BT raw milk. Notably, levels of spores in used bedding were positively related to those in unused bedding, and used bedding spore levels were positively related to those in BT raw milk. The results of this study increase the understanding of the levels and ecology of mesophilic and thermophilic spores in raw milk, emphasize the possible role of bedding as a source of spores on-farm, and present opportunities for dairy producers to reduce spore levels in BT raw milk.     

Effect of milk base and starter culture on acidification,texture, and probiotic cell counts in fermented milk processing

In the present work, the compared effect of milk base and starter culture on acidification, texture, growth, and stability of probiotic bacteria in fermented milk processing, was studied. Two strains of probiotic bacteria were used, Lactobacillus acidophilus LA5 and L. rhamnosus LR35, with two starter cultures. One starter culture consisted only of Streptococcus thermophilus ST7 (single starter culture); the other was a yogurt mixed culture with S. thermophilus ST7 and L. bulgaricus LB12 (mixed starter culture). For the milk base preparation, four commercial dairy ingredients were tested (two milk protein concentrates and two casein hydrolysates). The resulting fermented milks were compared to those obtained with control milk (without enrichment) and milk added with skim milk powder. The performance of the two probiotic strains were opposite. L. acidophilus LA5 grew well on milk but showed a poor stability during storage. L. rhamnosus LR35 grew weakly on milk but was remarkably stable during storage. With the strains tested in this study, the use of the single starter culture and the addition of casein hydrolysate gave the best probiotic cell counts. The fermentation time was of about 11 h, and the probiotic level after five weeks of storage was greater than 106 cfu/ml for L. acidophilus LA5 and 10(7) cfu/ml for L. rhamnosus LR35. However, an optimization of the level of casein hydrolysate added to milk base has to be done, in order to improve texture and flavor when using this dairy ingredient.     

Risk factors associated with bulk tank standard plate count,bulk tank coliform count,and the presence of Staphylococcus aureus on organic and conventional dairy farms in the United States

The purpose of this study was to assess the association of bulk tank milk standard plate counts, bulk tank coliform counts (CC), and the presence of Staphylococcus aureus in bulk tank milk with various management and farm characteristics on organic and conventional dairy farms throughout New York, Wisconsin, and Oregon. Data from size-matched organic farms (n = 192), conventional nongrazing farms (n = 64), and conventional grazing farms (n = 36) were collected at a single visit for each farm. Of the 292 farms visited, 290 bulk tank milk samples were collected. Statistical models were created using data from all herds in the study, as well as exclusively for the organic subset of herds. Because of incomplete data, 267 of 290 herds were analyzed for total herd modeling, and 173 of 190 organic herds were analyzed for the organic herd modeling. Overall, more bulk tanks from organic farms had Staph. aureus cultured from them (62% of organic herds, 42% conventional nongrazing herds, and 43% of conventional grazing herds), whereas fewer organic herds had a high CC, defined as ≥50 cfu/mL, than conventional farms in the study. A high standard plate count (×1,000 cfu/mL) was associated with decreased body condition score of adult cows and decreased milk production in both models. Several variables were significant only in the model created using all herds or only in organic herds. The presence of Staph. aureus in the bulk tank milk was associated with fewer people treating mastitis, increased age of housing, and a higher percentage of cows with 3 or fewer teats in both the organic and total herd models. The Staph. aureus total herd model also showed a relationship with fewer first-lactation animals, higher hock scores, and less use of automatic takeoffs at milking. High bulk tank CC was related to feeding a total mixed ration and using natural service in nonlactating heifers in both models. Overall, attentive management and use of outside resources were useful with regard to CC on organic farms. In all models except the organic CC model, we observed an association with the average reported somatic cell count from 3 mo before the herd visit, indicating that many of the regularly tested milk quality parameters are interconnected. In conclusion, we found that conventional and organic farms are similar in regard to overall herd management, but each grazing system faces unique challenges when managing milk quality.     

A scoping review of the testing of bulk tank milk to detect nonbacterial pathogens or herd exposure to nonbacterial pathogens in dairy cattle

In this scoping review, we characterized the literature reporting on the testing of bulk milk samples to detect microorganisms other than bacteria that can cause diseases in dairy cattle, including viruses, helminths, algae, and protozoa. A search strategy was completed by screening databases, conference proceedings, animal health agency websites, disease surveillance program websites, and handbooks of cattle-related diagnostic tests for potentially relevant articles. Two reviewers independently screened articles in English, Portuguese, or Spanish; original studies reporting on the testing of farm-level, unprocessed bulk milk samples for presence of pathogens or specific antibodies against agents other than bacteria that can cause diseases in cows were retained. From all studies, we used spreadsheets to extract relevant information, including pathogen screened, test used, and country of origin of bulk milk samples. Additionally, for studies reporting sufficient data to estimate test characteristics, we extracted detailed information about herd eligibility, testing protocol, and herd-level infection definition. A total of 8,829 records were identified, from which 1,592 were retained and assessed for eligibility, and 306 were included. Bovine viral diarrhea virus, Fasciola hepatica, Ostertagia ostertagi, and bovine herpesvirus 1 were the most frequently screened agents, reported from 107, 45, 45, and 33 studies, respectively. Sensitivity of bulk milk ELISA to detect herds with animals infected by bovine herpesvirus 1 ranged from 2 to 100%, and was affected mostly by antigen selection, cut-off adopted, herd vaccination status, and seroprevalence of lactating cows. Bulk milk ELISA had very high specificity to detect herds free of bovine leukemia virus, and varying sensitivity to detect herds with infected animals, which depended on the within-herd seroprevalence of lactating cattle. As for bovine viral diarrhea virus, in general, the sensitivity of bulk milk ELISA was moderate to high (>80%) when infection status was defined based on presence of persistently infected cattle or a high proportion of seropositive lactating cattle. Nevertheless, bulk milk ELISA was not able to distinguish infected and noninfected herds based on presence of seropositive unvaccinated weanlings. The PCR or quantitative PCR protocols employed had very low sensitivities (<40%) and very high specificities (>95%) to classify bovine viral diarrhea virus infection status of dairy herds. Sensitivity and specificity of bulk milk ELISA to classify herds with regards to presence of F. hepatica- or O. ostertagi-parasitized cattle were generally high and driven mostly by the definition of herd infection status. Conversely, bulk milk ELISA demonstrated varying characteristics to detect herds with or without Dictyocaulus viviparus-parasitized cattle, depending primarily on the antigen selected and presence of cattle with clinical signs of lungworm infection.     

Short communication: Correlation between within-herd antibody-prevalence and bulk tank milk antibody levels to Mycobacterium avium ssp. paratuberculosis using 2 commercial immunoassays

The objective of this study was to determine the correlation between the results obtained with the ELISA technique for antibodies to Mycobacterium avium ssp. paratuberculosis in serum and bulk tank milk at the herd level. For this purpose, 203 samples of bulk tank milk were analyzed with 2 commercial ELISA from dairy herds with a prevalence of seropositive animals that was also determined. In regard to the reference test (results in blood serum), the sensitivity of the bulk tank milk test to detect high-positive herds (≥10% seroprevalence) ranged from 85.7 to 71.4%. The specificity to detect herds with no seropositive animals ranged from 70.5 to 53%. In a quantitative approach, Pearson correlation coefficients, reported as a measure of the linear association between herd seroprevalences and transformed optical density values recorded in bulk tank milk, were 0.39 and 0.54 for the studied ELISA. Although the test results were relatively fairly correlated with the within-herd prevalence, the practical utility of bulk tank milk testing for Mycobacterium avium ssp. paratuberculosis seems limited, especially regarding specificity.     

Short communication: Validation of a novel milk progesterone-based tool to monitor luteolysis in dairy cows using cost-effective,on-farm measured data

The progesterone (P4) monitoring algorithm using synergistic control (PMASC) uses luteal dynamics to identify fertility events in dairy cows. This algorithm employs a combination of mathematical functions describing the increasing and decreasing P4 concentrations during the development and regression of the corpus luteum and a statistical control chart that allows identification of luteolysis. The mathematical model combines sigmoidal functions from which the cycle characteristics can be calculated. Both the moment at which luteolysis is detected and confirmed by PMASC, as well as the model features themselves, can be used to inform the farmer on the fertility status of the cows.