Milk Flow Rate Research Articles

A new innovative process to produce lactose-reduced skim milk

The research field for applications for lactose hydrolysis has been investigated for some decades. Lactose intolerance, improvement for technical processing of solutions containing lactose and utilisation of lactose in whey are main topics in development of biotechnological processes. In this article, the establishment of a hollow fiber membrane reactor process for enzymatic lactose hydrolysis is reported. Mesophilic β-galactosidases were circulated abluminally during luminal flow of skim milk. The main problem, microorganisms growth in the enzyme solution, was minimised by sterile filtration and UV irradiation. In order to characterise the process parameters, such as skim milk concentration, enzyme activity and flow rates were varied. In comparison to a batch process, enzyme activity could be used longer and enzyme rest into the product should not occur. Furthermore, the three-dimensional separation of the substrate from the enzyme solution minimise blocking and washing out effects, which restrict processes with immobilised enzymes. A conversion rate of 78.11% was achieved at a skim milk flow rate of 9.9 l h −1, enzyme activity of 120 U ml −1 and a temperature of 23 ± 2 °C in a hollow fiber reactor with a membrane area of 4.9 m 2.

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.

Drying of a Dilute Suspension in a Revolving Flow Fluidized Bed of Inert Particles

Revolving air flow was generated by oblique holes on air distribution board in a fluidized bed dryer. Such a revolving air flow shows a large scale velocity fluctuation in radial as well as tangential directions. This turbulent flow of air can fluidize the inert particles with superior performance than vibrated fluidized bed. The revolving fluidized bed is simpler in fabrication and easier in operation. For two types of inert particles tested, 4 mm glass beads and 4 mm × 5 mm Teflon cylindrical extrudates, the volumetric heat transfer coefficients were found to increase with the liquid feed flowrate and air flow velocity but decrease with the air inlet temperature, height of static bed, and liquid concentration. The revolving fluidized bed gives an increase of volumetric heat transfer coefficient by 1 kW/m3 K, and represents a 15–25% enhancement from ordinary fluidized bed operated at a bed height of 60 mm, bed diameter of 140 mm, superficial air flow velocity of 3.5 m/s, liquid feed (Soya milk) flowrate of 20 mL/min at a concentration of 6.7%, and a temperature ranges of 80–140°C using Teflon extrudates as inert particles.

유우의 착유 지속시간과 유속에 미치는 요인 및 산유량과의 상관관계 추정에 관한 연구

The objective of this study was to investigate the environmental effects on duration time of milk flow, peak milk flow, and average milk flow in teats, and to estimate their relationships with milk yields in morning and evening milking, and to provide fundamental information for the further study on their relationships with clinical mastitis and somatic cell in milk. A total of 6,768 milking records were studied in 72 Holstein cows. The influences of season, parity, lactation month, and milking interval on characteristics of milk flow considering in linear model were significant(p < .05). Duration of milk flow was longest at milking in fall, past first parity and second month of lactation, and with milking interval over than 13.5hrs. Average milk flow rate and peak milk flow rate were highest at milking in summer, past first parity and 8 10 months of lactation, and with milking interval over than 13.5hrs. Milk flow rate was positively correlated to milk yield, and negatively correlated to the duration of milk flow. However duration milk flow was positively correlated to the milk yield with high level of correlation coefficient(+.60). For the establishment of optimum selection criteria on these traits, other aspects such as the udder health, disease and respective economic weights of milk flow characteristics in this study must be considered to develop the indices.

Pre-partum udder massaging as a means for reduction of fear in primiparous cows at milking

Influence of varying frequencies of pre-partum udder massaging (45, 30 or 15 massaging sessions on alternate days during last trimester of pregnancy) on temperament score, milk letdown time, milk flow rate and frequency of urination and defecation were observed in primiparous cows during first 76 days of lactation. Restlessness of animals while milking reduced significantly ( P < 0.05) in animals ( n = 18) exposed to pre-partum udder massaging compared to animals of control group ( n = 18). The median value of milk letdown time and milk flow rate varied from 23 to 31 s and 13 to 16 g/s, respectively in the massaged groups compared to 46–50 s and 8–9 g/s, respectively, in the control group, all the differences were significant ( P < 0.01). Both urination and defecation frequencies were significantly ( P < 0.05) high up to 16th day of lactation in the non-massaged group. It can be concluded that udder massaging for 30 sessions would reduce the level of fear in primiparous cows and also facilitate clean milk production.

Designing the automatic milking farm in a hot climate.

A mathematical simulation model was used to assist 5 farmers in developing design criteria for inclusion of robotic milking systems in each farm situation. The barn layout influences arrivals of cows to the milking robot as well as other cow traffic and must be carefully planned. Each farmer had individual objectives and consequently unique design criteria that determined the optimal solution. Planning factors addressed by simulations on these farms included: 1) optimal cow cooling locations; 2) optimal facility allocation in expanding dairies; 3) concentrate feeder locations and feeding management; 4) number of feeders--based on expected rations; 5) use of a robot in an open cowshed without free stalls; 6) number of robots needed, currently and in the future; 7) eight robots working in harmony; 8) robot locations that allow for expansion; 9) floor space needed in each barn section including maternity and veterinary treatment areas; 10) location of bottlenecks that limit efficiency or expansion; and 11) cow traffic routine as affected by management practices, feed allocation, and farm layout. The simulation allowed farmers to receive a course in managing a "virtual robotic milking farm" before installation of the barn. Therefore, each could be more confident that his future barn would work properly under his unique local conditions and management practices. One farm checked 2 yr after construction achieved an average daily robot utilization of 84%, nearly matching the 85% projected before the barn was built. Important variables considered in the simulations were facility allocation, cow space needed in each farm area, robot utilization, number of cows, milk yield, milk flow rate, feeding method and timing, robot location and orientation, and farm physical layout.

Effects of habituation to the milking parlour on the milk production and reproductive performance of first calving Holstein-Friesian and Norwegian dairy herd replacements

AbstractTwenty-nine Holstein-Friesian and 20 Norwegian dairy herd replacements were used to investigate the effect of habituating heifers to the milking parlour environment prior to calving on subsequent lactational performance. The heifers commenced the study at 3 weeks prior to calving when they were allocated on the basis of breed, genetic merit and live weight to either a habituation or no habituation (control) treatment. Heifers were housed together in cubicle accommodation with grass silage offered ad libitum along with 1 kg of concentrates per head per day offered in the feeding passage (control treatment) or in the food managers in the milking parlour (habituation treatment). Animals in the habituation treatment were exposed to the full milking parlour routine once daily (afternoon milking) in a 20-point rotary herringbone parlour. Holstein-Friesian heifers averaged 2.6 kg/day more milk than the Norwegian replacements. Holstein-Friesian heifers also had higher fat and protein yields than Norwegian heifers, however they also lost more body condition during the first 3 months of lactation. Habituated heifers yielded on average 1.3 kg/day more milk (P &lt; 0.001) than the control group of heifers over the first 100 days of lactation (26.7 v. 25.4 (s.e.d. 0.38) kg/day), with the difference being greatest in the first 2 to 3 weeks of lactation. In early lactation, animals on the habituation treatment lost more live weight (0.16 v. 0.02 (s.e.d. 0.061) kg/day) (P &lt; 0.05) and body condition than those on the control treatment. Duration of milking was longer (P &lt; 0.001) (378.4 v. 340.5 (s.e.d. 6.53) s) and milk flow rate slower (P &lt; 0.001) (2.20 v. 2.46 (s.e.d. 0.041) kg/min) respectively for the habituation compared with control group. Somatic cell counts (SCC) were lower (P &lt; 0.001) for habituation group (1.66 v. 1.79 (s.e.d. 0.037) log10SCC per ml), but there was no significant treatment effect on locomotion scores. Reproductive performance was lower for habituated heifers, with increased intervals to conception (P &lt; 0.05) (102 v. 83 (s.e.d. 9.22) days). Habituating heifers to the milking parlour environment prior to calving increased milk production but appeared to have some detrimental effects on reproductive performance.

Milk Leakage—An Increased Risk in Automatic Milking Systems

Milk leakage (ML), or milk observed dripping or flowing from one or more teats between milkings, has been associated with increased risk of udder infections and mastitis in dairy cows. Preliminary observations indicate that ML might occur more often in automatic milking systems (AMS) than in conventional milking systems (CMS), but comparative data on the incidence of ML in AMS or in CMS are not available. Therefore, the occurrence of ML at various observation periods was studied in one AMS with cows housed in a free-stall barn in comparison to CMS with cows housed either in a free-stall barn or a tie-stall barn and milked at regular intervals in a herringbone milking parlor. Relationships between ML and other cow and management factors were also examined. In each of 2 yr, all cows (n=230 total; 46 cows present both years) were observed at 2-h intervals during six 24-h periods. At least one ML occurred in 39.0 (AMS) vs. 11.2% (CMS) of individual cows and in 16.2 (AMS) vs. 2.9% (CMS) of 24-h cow days studied. Milk leakage was not related to milk production, parity, stage of lactation, or estrous status. However, in the AMS, 62% of primiparous and 28% of multiparous cows leaked milk at least once. Milk leakage occurred more often in rear than in forequarters. Cows were usually lying down when ML was observed, but intervals from previous milking varied, especially in AMS. In AMS, about one-fifth of the ML observations occurred ≤4h after milking, and half of those were associated with disturbances at the previous milking. Milk flow rate was higher in quarters leaking milk than in other quarters. Strategies to reduce milk leakage in AMS may be important to minimize potential risks of udder disease.

Oestrus detection in dairy cows based on serial measurements using univariate and multivariate analysis

Abstract. As visual oestrus detection is difficult to perform in large herds, different technical devices were developed to facilitate oestrus detection. In this investigation the significance of the traits activity, milk yield, milk flow rate and electrical conductivity due to oestrus was analysed. The traits were recorded automatically during each milking on a commercial dairy farm. Oestrus detection was performed for 862 cows on basis of time series consisting of 15 days before oestrus, the day of oestrus and 15 days after oestrus. The day of oestrus was determined by the insemination which caused a calving after 265 to 295 days. The univariate analyses of traits were performed by the time series methods day-to-day comparison, moving average, exponential smoothing and Box-Jenkins three parameter smoothing. For multivariate analyses a fuzzy logic model was developed and modified for the different combinations of traits. The efficiency of the detection models and traits was determined by the parameters sensitivity, specificity and error rate. A moving average was the best suited time series method for oestrus detection by activity data. Sensitivity ranged between 94.2 and 71% and error rate was between 53.2 and 21.5% for threshold values between 40 and 120%. The traits milk yield, milk flow rate and electrical conductivity were not suitable for univariate oestrus detection. Depending on the considered traits multivariate analyses resulted in sensitivities between 87.0 and 87.9%. The error rate varied between 28.2 and 31.0%. Further analyses should include previous information such as time since last oestrus.

Factors affecting mouthpiece chamber vacuum in machine milking

The vacuum in the mouthpiece chamber (MPC) was measured in a factorial trial with two liners (DeLaval 964008-01 and DeLaval 999007-03), two pulsator ratios (60 and 70%) and morning and evening milking over eight milkings of ten cows. Teat length and diameter were measured before and after milking, and maximum milk flow rate and depth of penetration of the teat into the teatcup were also recorded. The MPC vacuum at peak flow rate was classified as stable, at various levels, in 79% of the recordings. In the rest of the milkings the vacuum declined gradually, and this decline was associated with gradually deeper penetration of the teat into the teatcup. The DeLaval 964008-01 liner with the narrower bore and larger mouthpiece opening gave lower MPC vacuum at peak flow rate than did the wider bore DeLaval 999007-03 with the smaller mouthpiece opening. Morning milking gave higher MPC vacuum than evening milking. Increased maximum milk flow rate and increased length and diameter of the teat gave decreased MPC vacuum. The teats were longer before milking in the morning than in the evening. However, during peak flow rate, the teats had penetrated deeper into the teatcup in the evening than in the morning. A marked change in MPC vacuum in the transition to the period of flow rate can be used to identify the start of over-milking of an individual teat. A general model explaining the MPC vacuum as the outcome of the balance between air leakage past the mouthpiece lip and the leakage past the teat in the liner barrel is suggested.

Investigation of correlations and milking parameter distribution on cattle farms in eastern Croatia

Recently secondary cattle selection traits have been given more attention in developed cattle breeding countries in establishing a selection index. In this way, milking traits have acquired a prominent place. This paper aimed to determine coefficients of correlation and regression between a number of milking traits, that could be helpful in establishing a selection index for breeding bulls and their dams. A further goal was to determine the distribution of milking parameters. The data of 303 Holstein Friesian and 235 Simmental cows were analysed. The results showed that in both cow breeds correlations existed between milk yield and average milk flow (0.39 and 0.49), as well as between milk yield and milking time (0.53 and 0.35). Negative correlations were found between average milk flow and milking time (-0.49 and -0.56). For the Holstein Friesian breed, 67.0% of the cows had a total milk flow in the range of 1.61 to 3.60 kg/min, whereas in the Simmental breed 72.2% of the cows had a total milk flow of 2.40 kg/min. The milk flow rate can be indirectly affected by selecting cows with higher milk production. The definition of an optimal milk flow rate and the determination of breeding goals for milking traits will lead to faster progress in milking trait improvement and an easier choice of quality breeding bulls and dams.

INACTIVATION OF SELECTED MICROORGANISMS AND PROPERTIES OF PULSED ELECTRIC FIELD PROCESSED MILK

Raw skim milk and ultra-high-temperature (UHT) skim milk inoculated with Pseudomonas fluorescens, Lactococcus lactis and Bacillus cereus were processed by pulsed electric field (PEF) treatment. A continuous PEF bench scale system was set to deliver 35 kV/cm field strength with 64 pulses of bipolar square wave for 188 μs. The flow rate of milk was 1 mL/s. Milk temperature was raised to 52C and cooled to 22C during PEF treatment. Pasteurization at 73C for 30 s was used for comparison. Microbial inactivation and cell morphology were investigated. Analyses for protein, total solids, color, pH, particle size, density and electrical conductivity showed no significant effects (P > 0.05) in the PEF processed milk. PEF treatment accomplished a 0.3 to 3.0 log reduction of P. fluorescens, L. lactis and B. cereus in UHT milk and of total microorganisms in raw milk.

Milk Flow Rate and Milking Frequency in Red Sokoto Goats

Twenty-four Red Sokoto goats were hand milked for 120 days to determine milk flow rate. The does were grouped into three for once, twice and thrice a day milking to determine the effect of milkin g frequency on milk flow rate. The average daily milk yield and milk flow rate was 466.9g and 3.5g/sec, respectively. Milking frequency significantly (P<0.01) influenced milk yield and milk flow rate. The higher the milking frequency, the higher the milk yield, but with a decreasing flow rate. Milk yield and milk flow rate were significantly (P<0.01) and positively correlated (r = 0.88). Both milk yield and flow rate reached their peak at the 4 week of production. The optimum milking frequency for Red Sokoto goat in this study was the twice th daily milking, since there was 52.7% increase in milk yield from once a day, with a marginal 7.9% reduction in milk flow rate.

The effect of milk flow rate and milk allowance on feeding related behaviour in dairy calves fed by computer controlled milk feeders

The aim of this study was to investigate the effect of milk flow rate and milk allowance on calves’ use of a computer controlled milk feeder. Six blocks, each consisting of 16 calves, were used (Holstein–Friesian, Danish Red, and Jersey). Within each block, the calves were assigned to one of four treatments: low milk allowance and normal milk flow rate (LN), high milk allowance and normal milk flow rate (HN), low milk allowance and reduced milk flow rate (LR), or high milk allowance and reduced milk flow rate (HR). A low milk allowance consisted of 4.8 l of milk daily for the heavy breeds (Holstein–Friesian, Danish Red) and 2.8 l for Jersey, while high milk allowance were 8.0 l daily for the heavy breeds and 4.8 l for Jersey. The data collected automatically by the computer controlled milk feeder from day 15 until weaning showed that overall the combination of high milk allowance and reduced milk flow rate resulted in most time spent in the feeder during rewarded visits ( P<0.01). However, there were significant breed effects. For calves of the heavy breeds a reduced milk flow rate resulted in a longer duration of rewarded visits ( P<0.01) and in a longer duration of all visits ( P<0.05). Also for calves of the heavy breeds, a high milk allowance resulted in fewer unrewarded visits ( P<0.05), a shorter duration of unrewarded visits ( P<0.01), and a shorter duration of all visits to the feeder ( P<0.05). Furthermore, across breeds the reduced milk flow rate resulted in a longer duration of visits where the calves had access to milk but did not consume any ( P<0.05). The behaviour of the calves was recorded for 24 h using video. These recordings showed that for the heavy breeds, the calves fed at a reduced milk flow rate occupied the feeder more than calves fed at a normal milk flow rate ( P<0.05). The calves of the heavy breeds offered a high milk allowance entered a free feeder less often ( P<0.05) and also entered the feeder less frequently as soon as it was free ( P<0.05). Across breeds, the calves offered a low milk allowance in combination with a reduced milk flow rate tried more often to get access to an occupied feeder ( P<0.05) and displaced other calves from the feeder more often ( P<0.05). No effect of treatment was found on the occurrence of cross-sucking. The results show that for the heavy breeds, a reduced milk flow rate increased the mean occupancy of the feeder due to a longer duration of rewarded visits. Furthermore, for the heavy breeds a higher milk allowance reduced the mean occupancy through a reduction in the duration of unrewarded visits. These results support the hypothesis that a high number of unrewarded visits to computer controlled milk feeders may be due to hunger. They further suggest that the time the calves occupy the feeder may be reduced by a high milk allowance. The combination of a low milk allowance and a reduced milk flow rate may result in an increase in the competition for access to the feeder.

Sensors and management support in high-technology milking.

Two directions can be distinguished in the development of high-tech milking equipment: 1) high-capacity milking parlors with a high throughput of cows per person per hour and 2) automatic milking systems in which manual labor is replaced by a milking robot. High-capacity milking parlors are developed in such a way that one operator is able to milk many cows, partly by automation and partly by optimization of available labor. In such parlors, one operator can milk up to 125 cows per hour. This means that there are only a few seconds available for udder preparation. In an automatic milking system, a robot takes over all manual labor during milking. Currently available systems have one robot arm working with one milking stall (one-stall system) or one robot arm working with more milking stalls (multiple-stall systems). Cows have to go to the automatic milking system voluntarily. Therefore, there is a large variation in milking intervals. Moreover, a large variation between milkings and between cows was observed in milk flow rate, machine-on time and udder preparation time. Both developments in high-tech milking have effects on the milk ejection. The small amount of time dedicated to udder preparation in high-capacity milking parlors has negative effects on the milk ejection, among others leading to more bimodal milk flow curves and longer machine-on time. In automatic milking systems, the variation in time between udder preparation and cluster attachment and in milking frequency might have an effect on milk ejection. Lactation physiology can play a role in solving the questions around milk ejection in high-tech milking systems. The introduction of high-tech milking systems makes decision support systems using sensors necessary. These systems should assist in detection of abnormal milk and mastitis. To a lesser extent, diseased cows need to be brought to the attention of the dairy farmer. Some sensors are currently available for this purpose, but they do not fulfill all demands. In the near future other sensors might be developed. It is important that this development is demand driven and not technology driven. Lactation physiology can play an important role in the determination of milk components useful for automatic detection.

Effects of habituation to the milking parlour on production, health and fertility of Norwegian and Holstein dairy herd replacements

During the transition period (defined as three weeks prior to calving to three weeks post-calving) heifers are exposed to physiological, nutritional, management, and social changes as they enter the dairy herd. One obvious change is the introduction of heifers to the milking parlour. Previous work has shown that when mature cows were milked in unfamiliar surroundings, milk yield, milk flow rate and milking duration were affected due to increased stress (Rushens, et al. 2001). The objective of the current study was to investigate the effects of habituating heifers to the milking parlour pre-calving on the subsequent performance of Holstein-Friesian and Norwegian dairy herd replacements.

The effects of feeding method, milk allowance and social factors on milk feeding behaviour and cross-sucking in group housed dairy calves

Cross-sucking is non-nutritive sucking of another calf’s body. This detrimental behaviour is seen in artificially reared calves, but never in calves reared by the dam. The behaviour stems from a redirection of the natural sucking behaviour. Studies of calves fed milk in buckets have shown that cross-sucking may be reduced if teat buckets are used instead of open buckets. Prolonging the milk meal by reducing the milk flow rate and leaving the teat buckets available after the meal ensure the largest reduction of cross-sucking. These results are predominantly based on investigations with calves housed individually, in pairs or in groups of three. Prolonging the milk meal by reducing the milk flow rate in calves fed by computer-controlled milk feeders also reduced the occurrence of cross-sucking. Under commercial conditions there are often 20–40 calves per feeding station and much aggression around and displacement from the feeding station is seen. Furthermore, there is much cross-sucking around the feeding station. A gate may be fitted to the feeding station that protects the calf from displacement and prevents cross-sucking on the calf in the station. It is noted that both reduced milk flow rate and gating the feeding station may reduce the capacity of the feeder. Under standard conditions the calves pay several unrewarded visits to the computer-controlled milk feeder and restricted milk feeding has been found to increase the number of unrewarded visits. Cross-sucking may also be motivated by hunger and the influence of milk allowance, as well as distribution of milk meals, on use of the feeder and cross-sucking should be investigated. Furthermore, future research should focus on what an appropriate number of calves per feeding station is for computer-controlled milk feeders to function optimally and to ensure minimal problems due to aggression and cross-sucking.

Systematic effects on activity, milk yield, milk flow rate and electrical conductivity

Abstract. The traits activity, milk yield, milk flow rate and electrical conductivity were analysed in preparation for automatic oestrus detection. Collection of data was performed on a commercial dairy farm and milking took place in a rotary milking parlour. Between February and December 1998 1,090,031 observations from 2,422 Holstein Friesian cows were accumulated. Around 30% of cows were milked thrice daily. For each trait and each cow a daily value was calculated. The fixed effects test day, parity, calving season, milking frequency, week of lactation and the random effect cow were considered in statistical analyses. With increasing number of parity, activity decreased and milk yield, milk flow rate and electrical conductivity increased. The milking frequency had significant influence on all analysed traits and for the effect calving season no consistent trend was found. All traits showed characteristic patterns during lactation. Between test days high variations were found for the trait activity. The remaining traits showed a steady level except for small fluctuations. Repeatability was 27.4% for activity and between 70 and 78.7% for the milk parameters. The repeatabilities verified the collected field data having a satisfying structure for application in automatic oestrus detection. The repeatability of the trait activity indicated high differences between and within cows. The right skewed distribution indicated the activity as a promising trait for further analyses.

Distribution of milk flow in Holstein Friesian and Fleckvieh cows in Croatia

Abstract. The aim was to investigate the distribution of milk flow rate in Holstein Friesian and Fleckvieh cattle. Researches were made in four farms in Eastern Croatia with 534 cows. 2594 tests were made with computer milking equipment, Alfa-Laval and with digital milk flow counter made by Tru-Test Company. The measuring of milk flow rates was done from 50th to 180th day of lactation. Tests showed as expected better results among Holstein Friesian then Fleckvieh cows. The optimal distribution of milk flow rate of Holstein Friesian type was 56.58 % and Fleckvieh was only 38.91 %. The results of the investigation are discussed. The milk flow rate represents an essential performance trait and should be included into the breeding program.

Individual Differences in Behavioral and Physiological Responsiveness of Primiparous Dairy Cows to Machine Milking

An experiment was performed in primiparous dairy cows (n=23) to examine consistency of individual differences in reactivity to milking, and correlations between measures of behavior, physiology, and milk ejection. Responsiveness to milking was monitored during the first machine milking, on d 2 of lactation, and during milkings on d 4 and 130 of lactation. Measurements included kicking and stepping behavior, plasma cortisol and plasma oxytocin, heart rate, milk yield, milking time, milk flow rate, and residual milk obtained after administration of exogenous oxytocin. With repeated early lactation milkings, residual milk and the incidence of abnormal milk flow curves decreased. On d 130 of lactation all heifers exhibited normal milk ejection. Except for higher plasma cortisol concentrations on d 2, all measures were consistent over time between d 2 and 4 of lactation as indicated by significant rank correlations. Individual differences in the behavioral response to udder preparation were consistent over time between early lactation milkings and d 130 of lactation. Residual milk, milk yield, maximum milk flow rate, plasma oxytocin and heart rate during udder preparation were similarly interrelated on d 2 and 4 of lactation. High heart rate responses on d 2 and 4 were associated with enhanced inhibition of milk ejection. In contrast, behavior recorded during the milking process was unrelated to ease of milk removal. Our results indicate that milking at the beginning of lactation may be stressful to some heifers, to the extent that milk ejection is inhibited, but less disturbing to others. The existence of consistent behavioral and physiological responses in the present study suggests that responsiveness of dairy heifers to milking is mediated by stable animal characteristics.