Optimally achieving milk bulk tank somatic cell count thresholds

High somatic cell count in milk leads to reduced shelf life in fluid milk and lower processed yields in manufactured dairy products. As a result, farmers are often penalized for high bulk tank somatic cell count or paid a premium for low bulk tank somatic cell count. Many countries also require all milk from a farm to be lower than a specified regulated somatic cell count. Thus, farms often cull cows that have high somatic cell count to meet somatic cell count thresholds. Rather than naïvely cull the highest somatic cell count cows, a mathematical programming model was developed that determines the cows to be culled from the herd by maximizing the net present value of the herd, subject to meeting any specified bulk tank somatic cell count level. The model was applied to test-day cows on 2 New York State dairy farms. Results showed that the net present value of the herd was increased by using the model to meet the somatic cell count restriction compared with naïvely culling the highest somatic cell count cows. Implementation of the model would be straightforward in dairy management decision software.     

Identification of dairy farm management practices associated with the presence of psychrotolerant sporeformers in bulk tank milk

Some strains of sporeforming bacteria (e.g., Bacillus spp. and Paenibacillus spp.) can survive pasteurization and subsequently grow at refrigeration temperatures, causing pasteurized fluid milk spoilage. To identify farm management practices associated with different levels of sporeformers in raw milk, a bulk tank sample was obtained from and a management and herd health questionnaire was administered to 99 New York State dairy farms. Milk samples were spore pasteurized [80°C (176°F) for 12 min] and subsequently analyzed for most-probable number and for sporeformer counts on the initial day of spore pasteurization (SP), and after refrigerated storage (6°C) at 7, 14, and 21 d after SP. Management practices were analyzed for association with sporeformer counts and bulk tank somatic cell counts. Sixty-two farms had high sporeformer growth (≥3 log cfu/mL at any day after SP), with an average sporeformer count of 5.20 ± 1.41 mean log₁₀ cfu/mL at 21 d after SP. Thirty-seven farms had low sporeformer numbers (<3 log cfu/mL for all days after SP), with an average sporeformer count of 0.75 ± 0.94 mean log₁₀ cfu/mL at 21 d after SP. Farms with >25% of cows with dirty udders in the milking parlor were 3.15 times more likely to be in the high category than farms with ≤10% of milking cows with dirty udders. Farms with <200 cows were 3.61 times more likely to be in the high category than farms with ≥200 cows. Management practices significantly associated with increased bulk tank somatic cell count were a lack of use of the California mastitis test at freshening and >25% of cows with dirty udders observed in the milking parlor. Changes in management practices associated with cow cleanliness may directly ensure longer shelf life and higher quality of pasteurized fluid milk.     

Results from raw milk microbiological tests do not predict the shelf-life performance of commercially pasteurized fluid milk

Analytical tools that accurately predict the performance of raw milk following its manufacture into commercial food products are of economic interest to the dairy industry. To evaluate the ability of currently applied raw milk microbiological tests to predict the quality of commercially pasteurized fluid milk products, samples of raw milk and 2% fat pasteurized milk were obtained from 4 New York State fluid milk processors for a 1-yr period. Raw milk samples were examined using a variety of tests commonly applied to raw milk, including somatic cell count, standard plate count, psychrotrophic bacteria count, ropy milk test, coliform count, preliminary incubation count, laboratory pasteurization count, and spore pasteurization count. Differential and selective media were used to identify groups of bacteria present in raw milk. Pasteurized milk samples were held at 6°C for 21 d and evaluated for standard plate count, coliform count, and sensory quality throughout shelf-life. Bacterial isolates from select raw and pasteurized milk tests were identified using 16S ribosomal DNA sequencing. Linear regression analysis of raw milk test results versus results reflecting pasteurized milk quality consistently showed low R² values (<0.45); the majority of R² values were <0.25, indicating small relationship between the results from the raw milk tests and results from tests used to evaluate pasteurized milk quality. Our findings suggest the need for new raw milk tests that measure the specific biological barriers that limit shelf-life and quality of fluid milk products.     

Longitudinal assessment of dairy farm management practices associated with the presence of psychrotolerant Bacillales spores in bulk tank milk on 10 New York State dairy farms

The ability of certain spore-forming bacteria in the order Bacillales (e.g., Bacillus spp., Paenibacillus spp.) to survive pasteurization in spore form and grow at refrigeration temperatures results in product spoilage and limits the shelf life of high temperature, short time (HTST)-pasteurized fluid milk. To facilitate development of strategies to minimize contamination of raw milk with psychrotolerant Bacillales spores, we conducted a longitudinal study of 10 New York State dairy farms, which included yearlong monthly assessments of the frequency and levels of bulk tank raw milk psychrotolerant spore contamination, along with administration of questionnaires to identify farm management practices associated with psychrotolerant spore presence over time. Milk samples were first spore pasteurized (80°C for 12 min) and then analyzed for sporeformer counts on the initial day of spore pasteurization (SP), and after refrigerated storage (6°C) for 7, 14, and 21 d after SP. Overall, 41% of samples showed sporeformer counts of >20,000 cfu/mL at d 21, with Bacillus and Paenibacillus spp. being predominant causes of high sporeformer counts. Statistical analyses identified 3 management factors (more frequent cleaning of the bulk tank area, the use of a skid steer to scrape the housing area, and segregating problem cows during milking) that were all associated with lower probabilities of d-21 Bacillales spore detection in SP-treated bulk tank raw milk. Our data emphasize that appropriate on-farm measures to improve overall cleanliness and cow hygiene will reduce the probability of psychrotolerant Bacillales spore contamination of bulk tank raw milk, allowing for consistent production of raw milk with reduced psychrotolerant spore counts, which will facilitate production of HTST-pasteurized milk with extended refrigerated shelf life.     

Effects of somatic cell count on quality and shelf-life of pasteurized fluid milk

Milk was collected from eight Holstein cows four times before and four times after intramammary infection with Streptococcus agalactiae. Postinfection milk had significantly higher somatic cell count (SCC) (849,000 cells/ml) than preinfection milk (45,000 cells/ml). High SCC raw milk had more lipolysis and proteolysis than low SCC raw milk. Pasteurized, homogenized, 2% fat milks from pre- and postinfection periods were stored at 5 degrees C and analyzed for lipolysis, proteolysis, microbial quality, and sensory attributes at 1, 7, 14, and 21 d post processing. During refrigerated storage, the average rates of free fatty acid increase (i.e., lipolysis) and casein hydrolysis in high SCC milk were, respectively, three and two times faster than those in low SCC milk. In general, standard plate counts, coliform counts, and psychrotrophic bacterial counts of both the high and low SCC milks remained low (<100,000 cfu/ ml) during 5 degrees C storage. Low SCC milk maintained high organoleptic quality for the entire 21-d shelf-life period. However, for high SCC milk, between 14 and 21 d, sensory defects were detected, which resulted in low overall quality ratings. The sensory defects mainly included rancidity and bitterness and were consistent with higher levels of lipolysis and proteolysis. Hence, mastitis adversely affected the quality of pasteurized fluid milk. It is recommended that the fluid milk industry consider implementation of premium quality payment programs for low SCC milks.     

Psychrotolerant spore-former growth characterization for the development of a dairy spoilage predictive model

Psychrotolerant spore-forming bacteria represent a major challenge regarding microbial spoilage of fluid milk. These organisms can survive most conventional pasteurization regimens and subsequently germinate and grow to spoilage levels during refrigerated storage. To improve predictions of fluid milk shelf life and assess different approaches to control psychrotolerant spore-forming bacteria in the fluid milk production and processing continuum, we developed a predictive model of spoilage of fluid milk due to germination and growth of psychrotolerant spore-forming bacteria. We characterized 14 psychrotolerant spore-formers, representing the most common Bacillales subtypes isolated from raw and pasteurized milk, for ability to germinate from spores and grow in skim milk broth at 6°C. Complete growth curves were obtained by determining total bacterial count and spore count every 24 h for 30 d. Based on growth curves at 6°C, probability distributions of initial spore counts in bulk tank raw milk, and subtype frequency in bulk tank raw milk, a Monte Carlo simulation model was created to predict spoilage patterns in high temperature, short time-pasteurized fluid milk. Monte Carlo simulations predicted that 66% of half-gallons (1,900 mL) of high temperature, short time fluid milk would reach a cell density greater than 20,000 cfu/mL after 21 d of storage at 6°C, consistent with current spoilage patterns observed in commercial products. Our model also predicted that an intervention that reduces initial spore loads by 2.2 Log₁₀ most probable number/mL (e.g., microfiltration) can extend fluid milk shelf life by 4 d (end of shelf life was defined here as the first day when the mean total bacterial count exceeded 20,000 cfu/mL). This study not only provides a baseline understanding of the growth rates of psychrotolerant spore-formers in fluid milk, it also provides a stochastic model of spoilage by these organisms over the shelf life of fluid milk, which will ultimately allow for the assessment of different approaches to reduce fluid milk spoilage.     

Low-cost,on-farm intervention to reduce spores in bulk tank raw milk benefits producers,processors, and consumers

Bacterial spores, which are found in raw milk, can survive harsh processing conditions encountered in dairy manufacturing, including pasteurization and drying. Low-spore raw milk is desirable for dairy industry stakeholders, especially those who want to extend the shelf life of their product, expand their distribution channels, or reduce product spoilage. A recent previous study showed that an on-farm intervention that included washing towels with chlorine bleach and drying them completely, as well as training milking parlor employees to focus on teat end cleaning, significantly reduced spore levels in bulk tank raw milk. As a follow up to that previous study, here we calculate the costs associated with that previously described intervention as ranging from $9.49 to $13.35 per cow per year, depending on farm size. A Monte Carlo model was used to predict the shelf life of high temperature, short time fluid milk processed from raw milk before and after this low-cost intervention was applied, based on experimental data collected in a previous study. The model predicted that 18.24% of half-gallon containers of fluid milk processed from raw milk receiving no spore intervention would exceed the pasteurized milk ordinance limit of 20,000 cfu/mL by 17 d after pasteurization, while only 16.99% of containers processed from raw milk receiving the spore intervention would reach this level 17 d after pasteurization (a reduction of 1.25 percentage points and a 6.85% reduction). Finally, a survey of consumer milk use was conducted to determine how many consumers regularly consume fluid milk near or past the date printed on the package (i.e., code date), which revealed that over 50% of fluid milk consumers surveyed continue to consume fluid milk after this date, indicating that a considerable proportion of consumers are exposed to fluid milk that is likely to have high levels spore-forming bacterial growth and possibly associated quality defects (e.g., flavor or odor defects). This further highlights the importance of reducing spore levels in raw milk to extend pasteurized fluid milk shelf life and thereby reducing the risk of adverse consumer experiences. Processors who are interested in extending fluid milk shelf life by controlling the levels of spores in the raw milk supply should consider incentivizing low-spore raw milk through premium payments to producers.     

Estimating milk loss based on somatic cell count at the cow and herd level

There is a direct relationship between elevated somatic cell count (SCC) in an individual cow milk production and milk loss. This relationship has been used at the herd level to estimate an overall herd milk loss due to subclinical mastitis and to use recovery of this lost milk as a financial benefit to cover the cost of intervention strategies to improve milk quality. The objective of this study was to estimate the recoverable milk revenue on a per cow basis for herds moving from one herd average SCC level to a newer, lower level. Test-day records from 1,005,697 dairy cows in 3,741 herds between 2009 to 2019 were used. Milk yield loss for each cow in each herd on test day was estimated using a mixed effects regression equation, and then summed to estimated total herd milk loss. These herd average daily milk loss estimates were then related to the bulk tank SCC, and the distribution of underlying individual cow SCC were examined. The distributions in daily herd milk loss for various bulk tank SCC values were generated, and estimates of recoverable milk loss were generated to simulate a herd moving from their current bulk tank SCC to a new lower level. The results indicate that estimates of total herd milk yield loss vary with the distribution of cow-level SCC and parity within the herd, so it is imperative that milk loss be calculated on a per cow basis. Further, the recoverable milk loss estimates based on moving to a lower bulk tank SCC where milk loss is still occurring was relatively small compared with the traditional assumption that all milk loss would be recovered, and less than most herd owners and advisors would expect.     

Genetic diversity of thermoduric spoilage microorganisms of milk from Brazilian dairy farms

When correctly pasteurized, packaged, and stored, milk with low total bacterial counts (TBC) has a longer shelf life. Therefore, microorganisms that resist heat treatments are especially important in the deterioration of pasteurized milk and in its shelf life. The aim of this work was to quantify the thermoduric microorganisms after the pasteurization of refrigerated raw milk samples with low TBC and to identify the diversity of these isolates with proteolytic or lipolytic potential by RFLP analysis. Twenty samples of raw milk were collected in bulk milk tanks shortly after milking in different Brazilian dairy farms and pasteurized. The mean thermoduric count was 3.2 (±4.7) × 10² cfu/mL (2.1% of the TBC). Of the 310 colonies obtained, 44.2% showed milk spoilage potential, 32.6% were proteolytic and lipolytic simultaneously, 31% were exclusively proteolytic, and 48 (36.4%) were only lipolytic. Regarding the diversity, 8 genera were observed (Bacillus, Brachybacterium, Enterococcus, Streptococcus, Micrococcus, Kocuria, Paenibacillus, and Macrococcus); there was a predominance of endospore-forming bacteria (50%), and Bacillus licheniformis was the most common (34.1%) species. Considering the RFLP types, it was observed that the possible clonal populations make up the microbiota of different milk samples, but the same milk samples contain microorganisms of a single species with different RFLP types. Thus, even in milk with a high microbiological quality, it is necessary to control the potential milk-deteriorating thermoduric microorganisms to avoid the risk of compromising the shelf life and technological potential of pasteurized milk.     

Use of microfiltration to improve fluid milk quality

The objectives of the research were to determine the growth characteristics of bacteria in commercially pasteurized skim milk as a function of storage temperature; to determine the efficacy of a microfiltration and pasteurization process in reducing the number of total bacteria, spores, and coliforms in skim milk; and to estimate the shelf life of pasteurized microfiltered skim milk as a function of storage temperature. For the first objective, commercially pasteurized skim milk was stored at 0.1, 2.0, 4.2, and 6.1 degrees C. A total bacterial count >20,000 cfu/mL was considered the end of shelf life. Shelf life ranged from 16 d at 6.1 degrees C to 66 d at 0.1 degrees C. Decreasing storage temperature increased lag time and reduced logarithmic growth rate of a mixed microbial population. The increased lag time for the mixed microbial population at a lower storage temperature was the biggest contributor to longer shelf life. For the second objective, raw skim milk was microfiltered at 50 degrees C using a Tetra Alcross M7 Pilot Plant equipped with a ceramic Membralox membrane (pore diameter of 1.4 microm). The 50 degrees C permeate was pasteurized at 72 degrees C for 15 s, and cooled to 6 degrees C. Bacterial counts of raw skim milk were determined by standard plate count. Bacterial counts of microfiltered and pasteurized microfiltered skim milk were determined using a most probable number method. Across 3 trials, bacterial counts of the raw milk were reduced from 2,400, 3,600, and 1,475 cfu/mL to 0.240, 0.918, and 0.240 cfu/mL, respectively, by microfiltration. Bacterial counts in the pasteurized microfiltered skim milk for the 3 trials were 0.005, 0.008, and 0.005 cfu/mL, respectively, demonstrating an average 5.6 log reduction from the raw count due to the combination of microfiltration and pasteurization. For the third objective, pasteurized microfiltered skim milk was stored at each of 4 temperatures (0.1, 2.0, 4.2, and 6.1 degrees C) and the total bacterial count was determined weekly over a 92-d period. At 6 time points in the study, samples were also analyzed for noncasein nitrogen and the decrease in casein as a percentage of true protein was calculated. After 92 d, 50% of samples stored at 6.1 degrees C and 12% of samples stored at 4.2 degrees C exceeded a total bacterial count of 20,000 cfu/mL. No samples stored at 0.1 or 2.0 degrees C reached a detectable bacterial level during the study. When the bacterial count was <1,000 cfu/mL, shelf life was limited because sufficient proteolysis had occurred at 32 d at 6.1 degrees C, 46 d at 4.2 degrees C, 78 d at 2.0 degrees C, and >92 d at 0.1 degrees C to produce a detectable off-flavor in skim milk produced from a raw milk with a 240,000 somatic cell count.     

Evaluation of test-day milk somatic cell count to predict intramammary infection in late lactation grazing dairy cows

The use of selective dry cow antimicrobial therapy requires precisely differentiating cows with an intramammary infection (IMI) from uninfected cows close to drying-off to enable treatment allocation. Milk somatic cell count (SCC) is an indicator of an inflammatory response in the mammary gland and is usually associated with IMI. However, SCC can also be influenced by cow-level variables such as milk yield, lactation number, and stage of lactation. In recent years, predictive algorithms have been developed to differentiate cows with IMI from cows without IMI based on SCC data. The objective of this observational study was to explore the association between SCC and subclinical IMI, taking cognizance of cow-level predictors on Irish seasonal spring calving, pasture-based systems. Additionally, the optimal test-day SCC cut-point (maximized sensitivity and specificity) for IMI diagnosis was determined. A total of 2,074 cows across 21 spring calving dairy herds with an average monthly milk weighted bulk tank SCC of ≤200,000 cells/mL were enrolled in the study. Quarter-level milk sampling was carried out on all cows in late lactation (interquartile range = 240–261 d in milk) for bacteriological culturing. Bacteriological results were used to define cows with IMI when ≥1 quarter sample resulted in bacterial growth. Cow-level test-day SCC records were provided by the herd owners. The ability of the average, maximum, and last test-day SCC to predict infection were compared using receiver operator curves. Predictive logistic regression models tested included parity (primiparous or multiparous), yield at last test-day, and a standardized count of high SCC test-days. In total, 18.7% of cows were classified as having an IMI, with first-parity cows having a higher proportion of IMI (29.3%) compared with multiparous cows (16.1%). Staphylococcus aureus accounted for the majority of these infections. The last test-day SCC was the best predictor of infection with the highest area under the curve. The inclusions of parity, yield at last test-day, and a standardized count of high SCC test-days as predictors did not significantly improve the ability of last test-day SCC to predict IMI. The cut-point for last test-day SCC that maximized sensitivity and specificity was 64,975 cells/mL. This study indicates that in Irish seasonal pasture-based dairy herds with low bulk tank SCC, the last test-day SCC (interquartile range days in milk = 221–240) is the best predictor of IMI in late lactation.     

Temporal trends in bulk tank somatic cell count and total bacterial count in Irish dairy herds during the past decade

The objective of this study was to document temporal trends in bulk tank somatic cell count (SCC) and total bacterial counts (TBC) in Irish dairy herds during the years 1994 to 2004. Three milk processors participated in the study, providing data on 2,754,270 individual bulk tank SCC and 2,056,992 individual bulk tank TBC records from 9,113 herds. Somatic cell counts decreased during the years 1994 to 2000, followed by an annual increase thereafter of more than 2,000 cells/mL. A tendency existed for TBC to decrease over time. Across all years, bulk tank SCC were the lowest in April and highest in November; TBC were the lowest in May and highest in December. The significant seasonal pattern observed in herd SCC and TBC was an artifact of seasonal calving in Ireland. In general, herds selling more milk had lower bulk tank SCC and TBC. Herds having the highest SCC (i.e., >450,000 cells/mL) and the lowest SCC (i.e., ≤150,000 cells/mL) both contributed substantially to the mean SCC of the milk pool collected by the milk processors. Derived transition matrices showed that between adjacent years, herds had the greatest probability of remaining in the same annual mean SCC or TBC category.     

Incidence, source and some properties of psychrotrophic Bacillus spp found in raw and pasteurized milk

Spores of psychrotrophic Bacillus spp were isolated from 58% of farm bulk tank milks and about 69% of pasteurized milks. Counts of Bacillus spp in about 10% of raw milk samples reached 1 × 10⁵ cfu/ml and above within seven days at 6°C. Psychrotrophic spore counts in pasteurized milks ranged from <0.5 to 170 spores/litre with an average of about 17/1. There was little correlation between the total bacterial count of the raw milk and presence of psychrotrophic Bacillus spores. There was some evidence that the bulk tank itself may be a source of contamination. The spores in pasteurized milk probably were not the result of postpasteurization contamination. The optimum germination temperature for psychrotrophic Bacillus spores was lower than that for spores of mesophilic strains. About 50% of the psychrotrophic Bacillus strains isolated from milk were capable of growth at 2°C.     

Associations among milk quality indicators in raw bulk milk

The objective of this study was to determine characteristics and associations among bulk milk quality indicators from a cohort of dairies that used modern milk harvest, storage, and shipment systems and participated in an intensive program of milk quality monitoring. Bulk milk somatic cell count (SCC), total bacteria count (TBC), coliform count (CC), and laboratory pasteurization count (LPC) were monitored between July 2006 and July 2007. Bulk milk samples were collected 3 times daily (n = 3 farms), twice daily (n = 6 farms), once daily (n = 4 farms), or once every other day (n = 3 farms). Most farms (n = 11) had direct loading of milk into tankers on trucks, but 5 farms had stationary bulk tanks. The average herd size was 924 cows (range = 200 to 2,700), and daily milk produced per herd was 35,220 kg (range = 7,500 to 105,000 kg). Thresholds for increased bacterial counts were defined according to the 75th percentile and were >8,000 cfu/mL for TBC, >160 cfu/mL for CC, and ≥310 cfu/mL for LPC. Means values were 12,500 (n = 7,241 measurements), 242 (n = 7,275 measurements), and 226 cfu/mL (n = 7,220 measurements) for TBC, CC, and LPC, respectively. Increased TBC was 6.3 times more likely for bulk milk loads with increased CC compared with loads containing fewer coliforms. Increased TBC was 1.3 times more likely for bulk milk with increased LPC. The odds of increased TBC increased by 2.4% for every 10,000-cells/mL increase in SCC in the same milk load. The odds of increased CC increased by 4.3% for every 10,000-cells/mL increase in SCC. The odds of increased CC increased by 1% for every 0.1°C increase in the milk temperature upon arrival at the dairy plant (or at pickup for farms with bulk tank). Laboratory pasteurization count was poorly associated with other milk quality indicators. Seasonal effects on bacterial counts and milk temperature varied substantially among farms. Results of this study can be used to aid the interpretation and analysis of indicators of milk quality intensively produced by dairy processors’ laboratories.     

Management of Wisconsin dairy herds enrolled in milk quality teams

A study was conducted to characterize Wisconsin dairy herds that enrolled in a team-based milk quality improvement program and to assess association of specific management practices with milking efficiency and milk quality. Management and financial data were obtained from dairy farms (n = 180) that participated in the program. Upon enrollment, herds reported a median bulk milk somatic cell count (SCC) of 333,500 cells/mL, an average of 125 lactating cows, and a mean rolling-herd average of 10,100 kg. Many management practices and bulk milk SCC were strongly associated with herd size and facility type. Managers of herds housed in freestall barns adopted more standardized procedures and recommended management practices compared with managers of herds housed in stall barns. Those managers also reported less bulk milk SCC and greater milk yields, and had a tendency for lower prevalence of subclinical mastitis and reduced estimates of the incidence of clinical mastitis. Managers of freestall herds received more quality premiums for milk shipped, estimated that they had fewer financial losses related to mastitis, and reported more efficient milking performance. A more efficient milking performance did not increase estimates of clinical mastitis or bulk milk SCC. In herds having freestalls, frequent training of employees seemed to be the fundamental factor that increased milking efficiency. Bulk milk SCC was positively associated with standard plate count, estimated rate of clinical mastitis, prevalence of subclinical mastitis, numbers of cows culled for mastitis, and estimated financial losses attributable to mastitis. Herds reporting high bulk milk SCC had an increased prevalence of subclinical mastitis, but incidence did not differ among bulk milk SCC categories. Overall, herds did not discuss milk quality frequently with dairy professionals, and herds having greater bulk milk SCC reported less consultation with their herd veterinarian.     

Monte Carlo simulation model predicts bactofugation can extend shelf-life of pasteurized fluid milk,even when raw milk with low spore counts is used as the incoming ingredient

Bacterial spores from raw milk that survive the pasteurization process are responsible for half of all the spoilage of fluid milk. Bactofugation has received more attention as a nonthermal method that can reduce the presence of bacterial spores in milk and with it the spoilage of fluid milk. The objective of this work was to determine the effectiveness of bactofugation in removing spores from raw milk and estimate the effect the spore removal could have on shelf-life of fluid milk. The study was conducted in a commercial fluid milk processing facility where warm spore removal was performed using one-phase bactofuge followed by warm cream separation and high temperature, short time pasteurization. Samples from different stages of fluid milk processing with and without the use of bactofuge were tested for total plate count, mesophilic spore count, psychrotolerant spore count (PSC), and somatic cell count. Results were evaluated to determine the count reductions during different stages of fluid milk processing and compare counts in fluid milk processed with and without bactofugation. Bactofugation on average reduced the total plate count by 1.81 ± 0.72 log cfu/mL, mesophilic spore count by 1.08 ± 0.71 log cfu/mL, PSC by 0.86 ± 0.59 log cfu/mL, and somatic cell count by 135,881 ± 43,942 cells/mL. Psychrotolerant spore count in final pasteurized skim milk processed with and without bactofugation was used to predict the shelf-life of the pasteurized skim milk using the Monte Carlo simulation model. Although PSC in the initial raw milk was already low (?0.63 ± 0.47 log cfu/mL), the predicted values from the simulation model showed that bactofugation would extend the shelf-life of pasteurized skim milk by approximately 2 d. The results of this study will directly help fluid milk processors evaluate the benefits of using bactofugation as an intervention in their plants, and also demonstrate the benefits of using mathematical modeling in decision making.     

Association between somatic cell count during the first lactation and the cumulative milk yield of cows in Irish dairy herds

Reduced potential milk yield is an important component of mastitis costs in dairy cows. The first aim of this study was to assess associations between somatic cell count (SCC) during the first lactation, and cumulative milk yield over the first lactation and subsequent lifetime of cows in Irish dairy herds. The second aim was to assess the association between SCC at 5 to 30 d in milk during parity 1 (SCC1), and SCC over the entire first lactation for cows in Irish dairy herds. The data set studied included records from 51,483 cows in 5,900 herds. Somatic cell count throughout the first lactation was summarized using the geometric mean and variance of SCC. Data were analyzed using linear models that included random effects to account for the lack of independence between observations, and herd-level variation in coefficients. Models were developed in a Bayesian framework and parameters were estimated from 10,000 Markov chain Monte Carlo simulations. The final models were a good fit to the data. A 1-unit increase in mean natural logarithm SCC over the first lactation was associated with a median decrease in first lactation and lifetime milk yield of 135 and 1,663 kg, respectively. A 1-unit increase in the variance of natural logarithm SCC over the first lactation was associated with a median decrease in lifetime milk yield of 719 kg. To demonstrate the context of lifetime milk yield results, microsimulation was used to model the trajectory of individual cows and evaluate the expected outcomes for particular changes in herd-level geometric mean SCC over the first lactation. A 75% certainty of savings of at least €199/heifer in the herd was detected if herd-level geometric mean SCC over the first lactation was reduced from ≥120,000 to ≤72,000 cells/mL. The association between SCC1 and SCC over the remainder of the first lactation was highly herd dependent, indicating that control measures for heifer mastitis should be preferentially targeted on an individual-herd basis toward either the pre- and peripartum period, or the lactating period, to optimize the lifetime milk yield of dairy cows.     

A 100-Year Review: The production of fluid (market) milk

During the first 100 years of the Journal of Dairy Science, dairy foods and dairy production dairy scientists have partnered to publish new data and research results that have fostered the development of new knowledge. This knowledge has been the underpinning of both the commercial development of the fluid milk processing industry and regulations and marketing policies for the benefit of dairy farmers, processors, and consumers. During the first 50 years, most of the focus was on producing and delivering high-quality raw milk to factories and improving the shelf life of pasteurized fluid milk. During the second 50 years, raw milk quality was further improved through the use of milk quality payment incentives. Due to changing demographics and lifestyle, whole fluid milk consumption declined and processing technologies were developed to increase the range of fluid milk products (skim and low-fat milks, flavored milks, lactose-reduced milk, long-shelf-life milks, and milks with higher protein and calcium contents) offered to the consumer. In addition, technology to produce specialty high-protein sports beverages was developed, which expanded the milk-based beverage offerings to the consumer.     

Shelf life of pasteurized microfiltered milk containing 2% fat

The goal of this research was to produce homogenized milk containing 2% fat with a refrigerated shelf life of 60 to 90 d using minimum high temperature, short time (HTST) pasteurization in combination with other nonthermal processes. Raw skim milk was microfiltered (MF) using a Tetra Alcross MFS-7 pilot plant (Tetra Pak International SA, Pully, Switzerland) equipped with Membralox ceramic membranes (1.4 μm and surface area of 2.31 m²; Pall Corp., East Hills, NY). The unpasteurized MF skim permeate and each of 3 different cream sources were blended together to achieve three 2% fat milks. Each milk was homogenized (first stage: 17 MPa, second stage: 3 MPa) and HTST pasteurized (73.8°C for 15 s). The pasteurized MF skim permeate and the 3 pasteurized homogenized 2% fat milks (made from different fat sources) were stored at 1.7 and 5.7°C and the standard plate count for each milk was determined weekly over 90 d. When the standard plate count was >20,000 cfu/mL, it was considered the end of shelf life for the purpose of this study. Across 4 replicates, a 4.13 log reduction in bacteria was achieved by MF, and a further 0.53 log reduction was achieved by the combination of MF with HTST pasteurization (73.8°C for 15 s), resulting in a 4.66 log reduction in bacteria for the combined process. No containers of MF skim milk that was pasteurized after MF exceeded 20,000 cfu/mL bacteria count during 90 d of storage at 5.7°C. The 3 different approaches used to reduce the initial bacteria and spore count of each cream source used to make the 2% fat milks did not produce any shelf-life advantage over using cold separated raw cream when starting with excellent quality raw whole milk (i.e., low bacteria count). The combination of MF with HTST pasteurization (73.8°C for 15 s), combined with filling and packaging that was protected from microbial contamination, achieved a refrigerated shelf life of 60 to 90 d at both 1.7 and 5.7°C for 2% fat milks.     

Short communication: Comparison of bulk milk, yield-corrected, and average somatic cell counts as parameters to summarize the subclinical mastitis situation in a dairy herd

In this study, the correlation was determined between the prevalence of high cow-level somatic cell count (SCC >250,000 cells/mL), a summary of the subclinical mastitis situation in a dairy herd, and 3 average herd SCC parameters: bulk milk SCC (BMSCC), yield-corrected test-day SCC (CHSCC), and the arithmetic average test-day SCC (HSCC) of the lactating herd. The herd prevalence of cows with an SCC of >250,000 cells/mL was calculated by using Dairy Herd Improvement data. Herds were included if BMSCC was sampled within 2 d of the Dairy Herd Improvement test day and if the BMSCC did not exceed 400,000 cells/mL. The interval between sampling, 0, 1, or 2 d, did not significantly influence the correlation between BMSCC and the prevalence of high SCC. The correlations between the prevalence of high SCC and BMSCC, yield-corrected test-day SCC, and HSCC, examined by using a linear regression model, were 0.64, 0.78, and 0.89, respectively. Therefore, it can be concluded that, based on the highest correlation, HSCC is a more appropriate parameter than BMSCC to summarize the average herd subclinical mastitis situation in a dairy herd.