Investigations of milk quality from teats with milk flow disorders

The objective of this study was to investigate the quality of milk from teats with milk flow disorders. Somatic cell count, pathogens, and signs of mastitis (>100,000 cells/ml and pathogens detected) were determined in the milk from all teats of the udder before treatment of the affected teat, as well as 1 and 6 mo later. Teats with milk flow disorders were compared to all of the other teats from the same udder. Before treatment, the SCC from affected teats was 4.3 million higher, the odds of detecting pathogens 6 times higher, and the odds of mastitis 11 times higher than in control teats (when adjusted for other significant explanatory variables). SCC and the risk of mastitis decreased after surgical treatment of the affected teats, whereas the chance of detecting pathogens was not affected. Six months after treatment, the SCC was 1.3 million higher, and the odds of mastitis 6.5 times higher than in control teats. Throughout the study period neither SCC, the odds of detecting pathogens, nor mastitis changed significantly in control teats. It may be concluded from this study that milk quality from teats with milk flow disorders is decreased before treatment and does not reach the milk quality from unaffected teats within 6 mo after treatment.     

Teat anatomy and its relationship with quarter and udder milk flow characteristics in dairy cows

Anatomical and functional characteristics of the teat are supposed to have considerable influence on milk flow performance. In the present study, various teat and milking characteristics in 148 quarters of 38 cows were analyzed via 3 different approaches. Teat canal length, teat wall thickness, and teat diameter were measured by ultrasound. In addition, the vacuum needed to open the teat canal (VO) was determined and milk flow profiles were measured in each quarter separately.Rear teats were shorter and thicker than front teats, whereas teat canal length and teat wall thickness did not differ according to quarter position. Milk yield and peak flow rate (PFR) were higher in rear than in front quarters. Teat canal length and VO were negatively correlated with PFR and average flow rate (AFR) but no correlations were observed between milkability traits and externally measurable teat characteristics like teat length or teat diameter.Individual milkability at an udder level is a complex characteristic that is determined by the milkability at a quarter level and the distribution of quarter milk yields. The anatomical and functional characteristics of single teats can partly explain the milk flow characteristics of individual quarters.     

The control of milk flow through the teats of dairy cows.

The effects of teat smooth muscles and pulsation on the control of rate of milk flow have been investigated in two split udder experiments during machine milking of dairy cows. When two teats were milked without pulsation, the peak flow rate was reduced by .132 kg/min for these teats and by .107 kg/min for the other two teats, which received good pulsation. Both of these reductions were statistically significant. This suggests that there is systemic control of the teat sphincter muscle. When systemic muscle control was removed by treatment with clenbuterol, a beta-agonist, all flow rates increased. However, when the proportion of the pulsation cycle for which milk flow can occur was considered, the actual flow rate for teats milked without pulsation was approximately 36% lower than that for teats milked with pulsation. This was independent of clenbuterol treatment, suggesting that this local control is independent of overall muscle tone.     

Comparative evaluation of SIMPL silicone implants and NIT natural teat inserts to keep the teat canal patent after surgery

The objective of this study was the comparative evaluation of SIMPL silicone implants and NIT natural teat inserts to keep the teat canal patent after teat surgery. The study was performed on 100 teats of 97 cows treated surgically for milk flow disorders. After surgery, 53 teats were administered with SIMPL and 47 with NIT, and rested for several days. Before treatment and 1 and 6 mo later quarter milk flow and milk yield were measured with Lactocorders; quarter milk was examined for somatic cell count (SCC), pathogens, and signs of mastitis (SCC > 100,000 and pathogens detected). Half a year after surgery milk flow, milk yield and SCC were equal from teats that had been inserted with SIMPL or NIT. The odds of detecting pathogens or signs of mastitis in the milk was lower in SIMPL than in NIT teats at this point in time. SIMPL teats stayed in the herd as long as NIT teats. Based on the results, it may be expected that teats inserted with a SIMPL or NIT do not differ long term in regards to milk flow, milk yield, SCC, and risk of removal from the herd. After the use of SIMPL, fewer pathogens may be detected in the milk long term than after the use of NIT.     

Technical note: Effects of attachment of hind teats before cleaning and attachment of front teats on milking characteristics in automatic milking systems

Milking characteristics differ between the 4 quarters of a dairy cow udder. In particular, milking time is mostly prolonged in hind quarters compared with front quarters because of the usually higher amount of stored milk. The standard milking routine (STDMR) in both conventional and automatic milking systems (AMS) consists of teat preparation of all 4 quarters, followed by attachment of the 4 teat cups, regardless of the distribution of milk between quarters. In the current study, an alternative teat preparation and milking routine (ALTMR) in AMS was tested, which consisted of cleaning and starting the milking of hind teats before cleaning and attachment of front teats. The hypothesis was based on the fact that hind quarters have usually a longer milking time than front quarters. Starting the milking of hind quarters while the front teats are being cleaned may reduce the difference in the end of milking between front and hind quarters and thus reduce total milking time. Both routines were tested on 5 Swedish dairy farms equipped with AMS in a 4-wk experiment in which treatments were alternated weekly. Total milk yield did not differ between treatments. Machine-on time (MOT) was longer in ALTMR than in STDMR because the difference in milking time between hind and front quarters was less than the time needed to prepare the front teats. However, the longer MOT in ALTMR was compensated by a shorter total preparation time, including the attachment of the first teat cup, as only the hind teats (instead of all 4 teats) were cleaned before milking was started. This resulted in a similar total milking time from start of cleaning of the first quarter until the end of milking of the last quarter in both treatments. Because of the prolonged MOT, average milk flow rate was lower in ALTMR than STDMR. Peak flow rate was higher in ALTMR than STDMR, but only in teat cups 1 (first attached, hind quarter) and 3 (third attached, front quarter), whereas main milk flow was higher in ALTMR than STDMR in both front quarters. In conclusion, splitting teat cleaning and the start of milking between hind and front quarters does not prolong total milking time, including teat cleaning. The partially positive effect on peak and main milk flow indicates that the ALTMR is a suitable milking routine in AMS. In herds with a greater difference of milk stored in hind compared with front quarters, a reduced total milking time can be expected for ALTMR.     

Sources of variation in milk flow characteristics at udder and quarter levels

The aim of this study was to describe and analyze effects of parity, stage of lactation, milkability (3 groups of cows with differing peak flow rates), time of milking, and quarter position on milk production and milk flow measures at udder and quarter levels. Particular emphasis was put on changes to the decline phase and in duration of overmilking. More than 75,800 quarter milk flow curves and more than 19,300 udder milk flow curves obtained from 38 cows throughout lactation were analyzed. Stage of lactation significantly influenced all studied variables at both udder and quarter levels. At the quarter level, the duration of decline phase and the decline ratio (decline phase as a percentage of milking time) decreased from mo 1 to 2 and then gradually increased as lactation advanced. In contrast, at the udder level, duration of decline phase decreased throughout lactation but beginning at mo 2, the decline ratio increased as lactation advanced. The duration of the overmilking phase of quarters increased from mo 1 to 3 and then decreased in the course of lactation. Parity did not influence peak and average flow rates, the duration of increase phase, or the decline ratio at either udder or quarter levels. All milk flow measures were higher during morning milking except the duration of increase and decline phases at the quarter level and the duration of increase phase at the udder level. Milk yield and the duration of increase phase were not affected by milkability at either level. Quarters from udders with high milkability had longest duration of decline phase and the shortest overmilking phase. Milkability did not influence duration of the decline phase at the udder level. Quarter position influenced all measured variables of milk yield and milk flow. Rear quarters had significantly higher milk yield, longer time of milking, higher peak, and higher average flow rates than front quarters. Front quarters had shorter duration of increase and decline phases than rear quarters. The duration of the overmilking phase was almost double for front quarters. There were also differences in measured flow rates between left or right quarters on respective front or rear positions. Measured characteristics reported in this study may be important in setting default parameters in automated milking systems.     

Factors affecting milk flow traits in dairy cows: results of a field study

The study of milk flow curves provides useful information for enhancing milking efficiency and protecting udder health by adapting milking machine and milking procedures to the physiological requirements of the cow. The aim of this experiment was to investigate, using field data, the relationships among traits of the milk flow curves, their sources of variation, and milking performances in terms of milk production, machine-on time, and udder health. A total of 2,486 milk flow curves of the whole udder were collected in 82 Italian Holstein-Friesian dairy herds in the Lombardy region of Italy. Approximately one-third (35.1%) of milk flow curves were classified as bimodal. Most flow characteristics were influenced by lactation number, days in milk, and peak flow but also strongly affected by premilking operations. Proper udder preparation, including forestripping and predipping, resulted in better milking performances compared with poor preparation, with greater milk yield per milking, shorter milking time, and lesser bimodality. Premilking delay time, between the start of teat stimulation and cup attachment, affected milking time significantly: The shortest milking time was obtained for a range of delay time between 1 and 60 s. As the delay time increased, the percentage of bimodality dropped significantly. Increasing the number of clusters per operator led to greater percentages of bimodal curves. The greater somatic cell count of cows with bimodal curves supports the hypothesis of the negative effect of bimodality on udder health and indicates the importance of avoiding its occurrence using proper pre-milking procedures.     

Visual detection of technical success and effectiveness of teat cleaning in two automatic milking systems

Technical success and effectiveness of teat cleaning and the management factors associated with them were evaluated in 9 automatic milking herds. In total, 616 teats cleaned with a cleaning cup and 716 teats cleaned with rotating brushes were included. Technical success and the effectiveness of teat cleaning, including the location and nature of the dirt, were evaluated visually. On average, 79.9% of teat cleanings with a cleaning cup, and 85.0% of those cleaned with brushes succeeded technically; that is, the teat was correctly positioned in the cleaning device throughout the whole cleaning process. The difference between use of teat cups and brushes was significant. However, because technical success of teat cleaning is strongly dependent on herd characteristics, these results should be interpreted with caution. Factors associated with the technical success of teat cleaning with a cleaning cup were herd, days in milk, behavior of the cow, teat color, and teat location. For rotating brushes, behavior of the cow, teat location, udder and teat structure, and days in milk were associated with technical success. Excessive udder hair and technical failure of the automatic milking machine also caused a few technically unsuccessful teat cleanings with a cleaning cup. Teats with technically successful teat cleanings were evaluated for the effectiveness of teat cleaning. From originally dirty teats, the cleaning cup had a significant advantage over the brushes in the percentage of teats that became clean or almost clean during the cleaning process (79.8 vs. 72.9%). Teat orifices were least effectively cleaned compared with the teat barrel and apex. Bedding material (peat, sawdust, or straw) on the teat was cleaned almost completely. Factors associated with the effectiveness of teat cleaning were teat cleanliness before cleaning, herd, teat cleaning method, and teat condition. The variation among herds indicates the likelihood that herd management factors can be adjusted to improve milking hygiene. There is also a need to improve the precision and effectiveness of the teat cleaning mechanisms of automatic milking systems.     

Correlated response of udder dimensions to selection for milk yield in Holsteins

Response to selection for milk yield in Holsteins was examined by a controlled selection experiment initiated in 1964. Foundation cows were paired by sire and divided randomly into two breeding groups, selection and control. Selection group was mated to four sires each year highest for Predicted Difference milk. Twenty bulls selected in 1964 as near breed average for milk sired all control cows. Milk yield was recorded for each lactation, and height of udder from ground, distances between teats, and perimeter and area bound by the four teats were measured at 30 to 75 days postpartum on 153 selection and 202 control cows over 14 yr. Most estimates of repeatability and heritability of udder dimensions before and after milking were .45 or larger. Correlations with milk yield were negative for udder height and positive for other udder measurements. Selection cows exceeded controls for lactational milk yield. Daughters of high milk bulls had greater distances between teats, greater perimeters, and larger areas of udder floor. Selection cows did not differ from controls in udder height for first parity but were below controls in udder height and had udders that collapsed more for all parities.     

Association of quarter milking measurements and cow-level factors in an automatic milking system

The primary aim of this observational study, in a single herd milked using multiple automatic milking system units, was to describe associations of quarter milk yield variability and quarter peak milk flow rate with cow-level factors. Information from the current lactation of 1,549 primiparous and multiparous cows was collected from January to December 2015. Data from each individual milking used in the analysis included quarter milk yield (QMY), udder milk yield, quarter peak milk flow rate (QPMF), quarter average milk flow rate (QAMF), quarter milking time, and milking interval. Milking interval and milk yield were used to calculate milk production rate (kg/h) at the quarter and udder levels. We investigated associations between QPMF and milking interval, QPMF and days in milk, and QMY and QAMF. A strong association between QPMF and both QAMF and milking interval was observed. A moderate association was found between QPMF and stage of lactation. However, QMY was not a useful indicator of QPMF because of the weak association observed between these variables. In this study, rear quarter QPMF was significantly increased by 3% compared with front quarter QPMF (1.45 vs 1.41 kg/min). Quarter milk yield was calculated as a percentage contribution of total udder milk yield per 10-d in milk window and ranked from lowest to highest contribution. Quarter contribution to udder milk yield showed a high level of variability, with 39% of animals having all 4 quarters change contribution rank at least once during part of or the whole lactation. Only 14% of cows were observed to have no change in quarter rank. When quarter contribution was assessed, irrespective of physical position of quarter within the udder, the percent of highest to lowest contribution across the lactation was relatively stable. The standard deviation of quarter milk production rate for each cow was regressed against the same cow's peak udder milk production rate, within a lactation, to ascertain whether quarter milk production rate variance could be used to predict peak udder milk production rate. Knowledge of the intra-udder quarter milk production rate standard deviation for an individual cow is not useful in predicting peak udder milk production rate. Quarter milking time appears to be a useful indicator to predict the optimal order of teatcup attachment. Analysis from this large, single-herd population indicates that QPMF is associated with the cow-level factors milking interval and days in milk, and that intra-udder QMY is highly variable.     

Milking time and risk of over-milking can be decreased with early teat cup removal based on udder quarter milk flow without loss in milk yield

Increasing the milk flow rate at which milking is terminated can shorten milking time and increase milking efficiency. The effects on milk yield and composition have not been fully investigated when the take-off is set at the udder quarter level and independent of feeding during milking. The objective of this study was to investigate the effect of 3 take-off levels at the udder quarter level (0.06, 0.3, and 0.48 kg/min) applied with or without feeding during milking on milking time, milk yield, the degree of udder emptying, milk composition, and free fatty acids. In this study, 30 cows were allocated into 6 groups, balanced by lactation number, lactation stage, and milk yield, and subjected to a 3 × 2 factorial arrangement of treatments using a Latin square design. Treatments were applied for 1 wk each. This study demonstrated milking time could be reduced by applying up to a take-off level of 0.48 kg/min on udder quarter level without losing milk yield or compromising milk composition or udder health.     

Interaction of somatic cell count and quarter milk flow patterns

Milk flow parameters at udder and quarter levels were studied in relation to somatic cell count (SCC) and other risk factors for mastitis (bimodality, duration of decline, and duration of overmilking phase). Thirty-eight Holstein cows in their first to sixth lactations were investigated during 10 mo of lactation. Monthly milk samples were collected for SCC during morning milking. Quarter and udder milk flows were recorded daily. A cow was included if one quarter was found to have an SCC higher than 200 × 10³ cells/mL. A total of 3,262 quarter milk flow curves and 804 udder milk flow curves from 22 cows (6 primiparous and 16 multiparous) were selected and evaluated. Selected data for milk flow profiles in relation to SCC represented 5 consecutive morning milkings around the time of milk sampling (sampling on d 3). A total of 661 milk samples were analyzed. At both the udder and quarter levels milk yield was reduced in groups with increased SCC. Quarters with high SCC (>500 × 10³ cells/mL) had lower peak flow rate and longer overmilking phases compared with quarters with low SCC (<200 × 10³ cells/mL). There was a tendency for a longer duration of the decline phase in quarters with high SCC but no effect was observed at the udder level. There were longer declines in bimodal milk flows at the quarter, but not at the udder, level. Also, quarters with bimodality had longer overmilking phases. The duration of the decline phases at the quarter level influenced all measured parameters except the duration of the increase phase. The quarters with a longer duration of the decline phase (≥80 s) had greater SCC and peak flow rate but had lower milk yield compared with quarters with a shorter duration of the decline phase (<27 s). Duration of the overmilking phase influenced all measured parameters except SCC. We conclude that for good udder health, the duration of the decline phase at the quarter level should be considered for milking parameters and udder preparation before milking.     

Cow-related risk factors for milk leakage

Milk leakage in dairy cows is a symptom of impaired teat sphincter function. Milk leakage is related to an increased risk of mastitis in heifers and cows, and causes hygiene problems. The aim of our study was to assess whether teat shape, condition of teat orifice, and peak milk flow rate are risk factors for milk leakage. We conducted a longitudinal observational study in 15 German dairy farms in which cows were maintained in loose housing. The farms were visited monthly at 2 consecutive milkings. During the evening milking, milk flow curves were measured with the LactoCorder. Milk leakage was recorded during the subsequent morning milking, when cows entered the milking parlor. Immediately after detachment of the milking cluster, teat shape, teat end shape, and condition of the teat orifice of cows were assessed between 9 and 100 d in milk (DIM) and during late lactation (>250 DIM). Data from 1600 cows were analyzed. Milk leakage was treated as the binary response variable in a logistic regression model with herd as a random effect. Primiparous cows with high peak milk flow and teat canal protrusion were at greater risk of milk leakage. High peak milk flow rate, short teats, teat canal protrusion, inverted teat ends, and early lactation increased the risk of milk leakage in multiparous cows. Random herd effects accounted for only 10% of the total variation, indicating that the impact of management or other herd-level factors on the occurrence of milk leakage is virtually negligible for practical purposes.     

Effects on milk yield of milking interval regularity and teat cup attachment failures with robotic milking systems

A database consisting of 35291 milking records from 83 cows was built over a period of 10 months with the objectives of studying the effect of teat cup attachment failures and milking interval regularity on milk production with an automated milking system (AMS). The database collected records of lactation number, days in milk (DIM), milk production, interval between milkings (for both the entire udder and individual quarters in case of a teat cup attachment failure) and average and peak milk flows for each milking. The weekly coefficient of variation (CV) of milking intervals was used as a measure of milking regularity. DIM, milking intervals, and CV of milking intervals were divided into four categories coinciding with the four quartiles of their respective distributions. The data were analysed by analysis of variance with cow as a random effect and lactation number, DIM, the occurrence of a milking failure, and the intervals between milkings or the weekly CV of milking intervals as fixed effects. The incidence of attachment failures was 7.6% of total milkings. Milk production by quarters affected by a milking failure following the failure was numerically greater owing to the longer interval between milkings. When accounting for the effect of milking intervals, milk production by affected quarters following a milking failure was 26% lower than with regular milkings. However, the decrease in milk production by quarters affected by milking failures was more severe as DIM increased. Average and peak milk flows by quarters affected by a milking failure were lower than when milkings occurred normally. However, milk production recovered its former level within seven milkings following a milking failure. Uneven frequency (weekly CV of milking intervals >27%) decreased daily milk yield, and affected multiparous more negatively than primiparous cows.     

Investigations on teat canal length in teats with milk flow disturbances

The objective of this study was to evaluate teat canal length as a test for tissue ruptures in the area of the teat canal in teats with milk flow disturbances (Medl's test). A total of 133 dairy cows affected with milk flow disturbances in one teat were used for this study. The teat canal length of the affected teat was compared with the teat canal length of the contralateral teat of the same cow. Milk flow disturbances were diagnosed by endoscopy. Diagnoses were categorized as tissue ruptures in the area of the teat canal or other causes such as narrowing of the teat canal, or free foreign bodies in the teat cistern. The median teat canal length was 11 mm in teats with milk flow disturbances, and 8 mm in contralateral control teats. When the test criterion was lengthening of the teat canal by > or =2 mm, 79% of the teat canals with tissue ruptures tested positive (true positive), but 47% of teat canals without tissue ruptures also tested positive (false positive). When the test criterion was unchanged teat canal length, 47% of teat canals with tissue ruptures tested positive, and only 7% of teat canals without tissue ruptures tested positive. Thus, it is concluded that Medl's test may be useful in differentiating causes of milk flow disturbances. However, a more accurate diagnosis may be made by teat endoscopy.     

Effects of premilking udder preparation on bacterial population, sediment, and iodine residue in milk

Udder preparations that wet both udder surfaces and teats had the highest standard plate count in milk compared with methods that wet teats only. Physical action of cleaning teats with a dry towel lowered bacterial count compared with preparations wetting both udder surfaces and teats. Methods resulting in lowest bacterial counts were the use of water hose, wet towel, or premilking disinfectant teat dip followed by drying with paper towels. Counts of coliform and Staphylococcus sp. followed similar trends. In most comparisons, addition of udder wash sanitizer was of marginal or no benefit. Standard plate count of teat rinses after udder preparation confirmed the benefit of cleaning and drying teats. Physical manipulation of teats during cleaning was essential for lowering sediment in milk. Drying of teats with a paper towel for at least 10 s after dipping with a 1% iodophor disinfectant dip was essential for reducing iodine residue. Both premilking and postmilking disinfectant teat dipping with a 1% iodophor teat dip caused higher iodine residue in milk than premilking disinfectant dip with subsequent drying. A .5% iodophor teat dip contributed less iodine in milk than a 1% iodophor teat dip. Premilking udder preparation affects bacterial count, sediment, and iodine residue in milk.     

Effects of cleaning duration and water temperature on oxytocin release and milk removal in an automatic milking system

Four different methods of teat preparation during milking in an automatic milking system were studied in 2 experiments on Red Holstein/German Fleckvieh cross-breed cows. Milking routines used were milking: 1) without premilking teat preparation; 2) with one cleaning cycle (58 to 60 s) with cold (13 to 15 degrees C) water; 3) with one cleaning cycle with warm water (30 to 32 degrees C); or 4) with 2 cleaning cycles (122 s) with warm water. In experiment 1, milking characteristics were evaluated and milking routines were randomly assigned to 62 cows during 3 measuring periods of 24 h each. In experiment 2, 10 randomly selected cows were assigned to the same milking routines during 4 d and blood samples for oxytocin (OT) determination were taken during milking in addition to milk flow recording. Milk production, peak flow rate, total, and quarter milk yields showed no differences among treatments. Premilking preparation with cold water compared with warm water showed no differences in OT release, milk yield, peak flow rate, main milking time, average flow rate, or time until main milk flow. Baseline OT concentrations were consistently low. At the start of teat cup attachment without premilking teat preparation OT concentrations remained on the basal level but were elevated in all other treatments. By 30 s from the start of milking, OT concentrations were markedly increased in all treatments and were no longer different between treatments. In conclusion, the teat cleaning device used in the automatic milking system, either with warm or cold water, was suitable to induce milk ejection in cows before the start of milking.     

Best combination of pre-stimulation and latency period duration before cluster attachment for efficient oxytocin release and milk ejection in cows with low to high udder-filling levels

Experiments were designed to investigate the suitability of a combination of a short manual teat stimulation with a short latency period before teat cup attachment to induce and maintain oxytocin release and milk ejection without interruption. In Experiment 1, seven dairy cows in mid lactation were manually pre-stimulated for 15, 30 or 45 s, followed by either 30 s or 45 s of latency period. It was shown that all treatments induced a similar release of oxytocin without interruption until the end of milking. In particular, the latency period of up to 45 s did not cause a transient decrease of oxytocin concentration. In Experiment 2, milking characteristics were recorded in seven cows each in early, mid, and late lactation, respectively. Because the course of milk ejection depends mainly on the degree of udder filling, individual milkings were classified based on the actual degree of udder filling which differs between lactational stages but also between morning and evening milkings. All animals underwent twelve different udder preparation treatments, i.e. 15, 30, or 45 s of pre-stimulation followed by latency periods of 0, 30, 45, or 60 s. Milking characteristics were recorded. Total milk yield, main milking time and average milk flow rate did not differ between treatments if the degree of udder filling at the start of milking was >40% of the maximum storage capacity. However, if the udder filling was <40%, main milking time was decreased with the duration of a latency period up to 45 s, independent of duration of pre-stimulation. Average milk flow at an udder filling of <40% was highest after a pre-stimulation of 45 s followed by a latency period of another 45 s. In contrast, average milk flow reached its lowest values at a pre-stimulation of 15 s without additional latency period. However, average milk flow after a 15-s pre-stimulation increased with increasing latency period. In conclusion, a very short pre-stimulation when followed by a latency period up to 45 s before teat cup attachment remains a suitable alternative for continuous stimulation to induce milk ejection.     

The interplay of continuous milk ejection and milking system with and without prestimulation at different vacuum settings

Efficient machine milking requires an optimal interaction of alveolar milk ejection in the udder and milk removal by the milking machine. The aim of the present study was to test whether the equilibrium between continuous milk ejection and milk removal can also be maintained at very fast milking through a particularly high vacuum. Eight Holstein dairy cows were milked at 42, 52, or 60 kPa, with (PS) or without (nPS) prestimulation. Each of the 6 treatments was conducted at 2 afternoon milkings in each animal. The prestimulation lasted 40 s and consisted of forestripping and teat cleaning. The cluster attachment followed after a 20-s latency period. Throughout each milking, B-mode ultrasound videos of the gland cistern of 1 front quarter as well as milk flow and claw vacuum curves were recorded. Total milk yield was neither affected by nPS or PS nor by the vacuum level. Milk removed within the first minute and the first 2 min of milking and average milk flow were higher, and the duration of incline and time until peak milk flow were shorter at PS than at nPS milkings at all vacuum levels. Machine-on time was shorter at PS than at nPS milkings, although only at 42 and 52 kPa vacuum, obviously caused by the high percentage of bimodalities occurring in nPS milkings (17% bimodalities in PS vs. 92% bimodalities in nPS milkings). The frequency of bimodalities was higher at high than at low vacuum both in PS and nPS milkings. Peak flow rate and average milk flow were both higher at higher vacuum levels. The duration of milk flow plateau was shorter at 60 kPa than at 42 kPa milkings. At the highest vacuum (60 kPa), the shorter plateau phase indicated a declining milk ejection rate toward the end of the plateau phase, and milk ejection could no longer keep up with the fast milk removal; hence, a higher milking efficiency at a higher vacuum level could only be achieved as long as the gland cistern remained sufficiently filled by the continuous milk ejection. The ultrasound imaging confirmed this finding as the duration of cisternal area plateau in the recorded front quarter was shorter at high than at low vacuum. Thus, the highest vacuum of 60 kPa did not cause a shorter machine-on time than 52 kPa. In conclusion, milking at a very high vacuum can increase milking efficiency compared with a low vacuum. However, a vacuum reduction at the start and toward the end of milking is required to prevent overmilking if milking is performed at a very high vacuum.