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* Department of Ruminant and Porcine Diseases, National Veterinary Institute, SE-751 89 Uppsala, Sweden,
Department of Obstetrics and Gynaecology, and
Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, SE-750 07 Uppsala, Sweden
Corresponding author: K. Persson Waller; e-mail: Karin.Persson-Waller{at}sva.se.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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4 h 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.
Key Words: automatic milking systems • dairy cow • milk leakage • udder health
Abbreviation key: AMU = automatic milking unit, AMS = automatic milking system, CMS = conventional milking systems, FSB = free-stall barn with cows milked in a milking parlor, ML = milk leakage, TSB = tie-stall barn with cows milked in a milking parlor, UDS = udder disease score
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Milk leakage can occur if the closing mechanism of the teat canal is compromised, such as when the teat end is damaged (Jørstad et al., 1989). However, the patency of the teat canal can also be affected by its anatomy because wide (McDonald, 1975; Jørstad et al., 1989) and short (Lacy-Hulbert and Hillerton, 1995) teat canals have been associated with a higher incidence of mastitis. Milk leakage can also occur if the internal milk pressure overcomes the closing forces of the teat canal (e.g., when the milk let-down reflex is activated before milking). Moreover, milking routines and conditions (e.g., vacuum and pulsation levels, liner design, and weight of cluster) are important for successful emptying of the udder at milking (Hamann and Dodd, 1992; Mein, 1992).
An AMS relies on well-functioning cow traffic between the automatic milking unit (AMU) and the feeding and resting areas. However, unlike a CMS, where milking frequency and interval are similar for all cows, there is more variation between and within cows in milking time and frequency, and in intervals between milkings in an AMS. Uneven milking intervals can influence both milk yield (Ipema et al., 1997) and milk SCC (Hamann and Gyodi, 2000), but the effect on the incidence of ML is not known. In AMS, quarters are often milked individually, which minimizes overmilking and is positive for udder health (Seeman 1997; Berglund et al., 2002). However, early studies showed that failure of milking cluster attachment during milking could occur in up to 15% of the milkings (Mottram et al., 1995; Ipema et al., 1997). This can result in no milking or incomplete milking of one or more quarters, which might result in increased risk of ML. However, no differences in strip yield (Svennersten-Sjaunja et al., 2000) or residual milk (Hopster et al., 2002) were observed when comparing conventional and automatic milking.
Use of AMS has increased in many countries. Studies including AMS farms in different countries indicate that herd udder health, as measured by SCC, may decline after introduction of the new system (Everitt et al., 2002; Kruip et al., 2002; van der Vorst and de Koning, 2002). However, it has also been demonstrated that the udder health was not negatively affected in some individual herds, which had good udder health at the introduction of AMS (Svennersten-Sjaunja et al., 2000; Hamann and Reinecke, 2002). Reasons behind observed increases in SCC in several farms are not fully clear, but an increased occurrence of ML in such systems could be one factor of importance. Data on the incidence of ML in AMS in comparison with the incidence in CMS are, to our knowledge, not available. Therefore, the primary aim of this 2-yr study was to compare the occurrence of ML in an AMS in comparison with 2 other groups of cows managed using a CMS. A second objective was to identify cow and management factors associated with higher risks of ML.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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The number of individual cows and cows per observation occasion varied among the barns and years studied (Table 1
). Overall, no statistically significant differences in parity, lactation month, or daily milk production were observed among barn systems. The overall proportions of cows in parity 1, 2, 3, and 
4 were 45, 23, 16, and 16%, respectively. However, the proportion of first-lactation cows in the barns was 31, 79, and 39% in AMS, FSB, and TSB, respectively, when combining data from both years. The high proportion of first-lactation cows in the FSB was due to management decisions. Due to this discrepancy, caution must be taken when comparing ML occurrence between the FSB and the other systems.
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Feeding
In the AMS, the feeding areas were reached either by passing through the AMU or by passing through selection gates. Silage only (yr 1) or a mix of silage, concentrate, and hay (yr 2) was fed ad libitum, whereas concentrates were fed individually in automatic feeding stations according to milk production. Feed troughs were filled at 4- to 5-h intervals between 0530 and 1830 h. In the FSB, cows were fed a mix of silage, concentrate, and hay four times per day (at 0430, 0900, 1400, and 1700 h). In the TSB, cows were fed silage and concentrates four times per day (at similar times as FSB), plus 1 kg of hay in the mornings. Daily supplementation of vitamins and minerals was given ad libitum from separate feed troughs in AMS and FSB, and individually in TSB.
Description of the Study
The study was performed in January and February in 2001 and 2002. The time of year was selected as most cows were high producing and the farm routines were stable and not affected by factors like calving or grazing seasons. All cows were observed by the same person at 2-h intervals during six 24-h periods spread over 3 to 4 wk (i.e., 72 observation periods per year). If the cow was lying down, the udder was gently lifted to enable inspection of all teats. At the start of the study periods, none of the cows had any visible traumatic teat injuries.
Milk leakage was defined as milk observed dripping or flowing from one or more teats. If ML were observed, the following variables were recorded for the affected cow: cow number, teat(s) with leakage, lying/standing, activity, and place in barn. In the second year, the position (lying/standing) of cows not leaking milk was also registered at all occasions. For each occasion of ML, the time from the previous milking (precise estimate in AMS and approximate estimates in FSB and TSB) was calculated. Additional data for all cows were collected, or calculated, using monthly milk recordings and other information in the herd database (Table 2).
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On a separate occasion at the end of the study period each year, one person examined the shape and condition of the teat ends of all cows. The shape of teat ends was classified as round, flat, or pointed, and the condition (no, smooth, or rough callosity rings) of teat ends was classified according to Neijenhuis et al. (2000).
Statistics
Data were evaluated for udder quarter, cow, observation, and/or cow-day (24-h period/cow), and are presented as means and standard deviations (SD). Each cow’s SCC was log10-transformed before analyses to ensure normal distribution of the data. Differences between cows with or without ML in parity, lactation month, daily milk production, SCC, and UDS were evaluated statistically using one-way ANOVA (Statistica, StatSoft, Inc., Tulsa, OK). Differences between barns in cow-days and individual cows with ML, effect of increasing UDS on risk for ML, differences between cows lying or standing, fore- and hind-udder quarters, and the relationship between ML and milk flow rate in AMS were analyzed using the GLM procedures (SAS Institute, Cary, NC) after correction for cow when necessary.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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. Including both years, proportions of cow-days (P < 0.001) and individual cows (P < 0.001) with ML on at least one occasion during the study period were significantly higher in AMS than in either TSB or FSB. Differences between the TSB and FSB were not significant. However, because mainly primiparous cows were present in the FSB, the data must be interpreted with caution. Three of 46 cows present both years leaked milk both years.
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3 times during the study periods was 44% in AMS, but only 14% in TSB and FSB (Table 4). In TSB and FSB, the highest number of ML per time point was observed just before morning milking, which started at 0530 h (Figure 1). Afternoon milking started at 1600 h in those groups. Distribution of ML was more variable over time in AMS (Figure 1). More details about the time of ML in relation to the previous milking are given below (Milking-Related Factors).
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Cow Factors
Including all cows from both years, the lactation number, lactation month, and daily milk production did not differ significantly between cows with or without ML (Table 5). However, the proportion of primiparous cows with at least one ML was 62, 15, and 3% in AMS (n = 34), FSB (n = 41), and TSB (n = 29), respectively. Corresponding numbers for multiparous cows were 28, 9, and 14% for AMS (n = 71), FSB (n = 11), and TSB (n = 42), respectively. In AMS, among cows with at least one ML, 48% of the primiparous cows and 45% of the multiparous cows leaked milk 3 times.
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It was significantly (P < 0.001) more common that cows lying down (104 of 3558 observations) leaked milk than cows standing up (14 of 3690 observations), according to observations in yr 2. There was no indication that the cows’ lying/standing behavior differed between the barns. The proportion of observations with cows lying down varied between 47 and 51% in the three barns. The cows were lying down in 85% (yr 1) and 92% (yr 2) of the ML observations. For 57% (yr 1) and 39% (yr 2) of the observations of ML when lying down, the cows were ruminating. For the remaining occasions, they were resting or sleeping.
Milking-Related Factors
Among the observations of ML, the time in relationship to the previous milking varied, especially in the AMS (Table 6). In yr 1, the mean (SD) time from previous milking was 7.6 (4.2) h, 13 h (n = 1), and 7.3 (1.5) h for AMS, FSB, and TSB, respectively. For yr 2, the corresponding values were 8.3 (4.1) h, 9.8 (1.7) h, and 9.5 (3.0) h, respectively. In the AMS, 22 and 15% of the total number of observations were made 4 h and >12h after milking, respectively (Table 6). When combining both years, 57% of the ML observations were made in primiparous cows and 43% in multiparous cows. In primiparous cows, 19, 27, 39, 13, and 1% of the ML observations (n = 89) were made 4 h, >4 to 8, >8 to 12, >12 to 16, and >6 h after milking, respectively. The corresponding proportions for the ML observations (n = 67) in multiparous cows were 25, 33, 25, 13, and 3%, respectively.
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4, >4 to 8, >8 to 12, >12 to 16, and >6 h after milking, respectively. Missed or incomplete milking was registered at least once in 4 of 22 (18%) cows with one or two ML, and in 11 of 19 (58%) cows with 3 ML. In a majority of the latter cows, such milking-related problems had occurred at most ML occasions. The relationship between the number of ML and these milking problems were similar in primiparous and multiparous cows (data not shown). Other problems registered in association with ML were cleaning of the AMU (n = 1), cow chased off the waiting area (n = 1), and abnormal milk quality (as defined by the Voluntary Milking System) (n = 3). The first two problems would have resulted in a longer waiting time for the cow and thereby in a longer milking interval. The abnormal milk quality indicates mastitis, which can lead to a reduced milk let down. At 2 occasions of ML that occurred 9 to 11 h after the previous milking in 1 cow, that cow had been moved to the AMS the same morning, and on 3 occasions (occurring >8 h postmilking) in 2 cows, the animals had passed the milking unit just before the time for a new milking permission.
During the second year, AMS data on the mean and peak milk flow rate were available for each cow and for individual quarter within cow. No such data were available in the FSB and TSB. No significant differences were observed between cows with at least 1 ML and cows without ML in their mean average and maximal flows. However, when comparing quarters with or without ML, the mean (P < 0.001) and peak (P < 0.01) flow rate per quarter was significantly higher in quarters with ML. The average (SD) mean and peak flow rates for udder quarters not leaking milk were 629 (199) g/min and 986 (210) g/min, respectively. The corresponding values for udder quarters with at least one ML were 776 (278) and 1138 (316) g/min, respectively. The effect of ML frequency observed per quarter on the milk flow rate was also analyzed after dividing the ML quarters in 3 groups, 1 ML, 2 ML, and 3 ML. Both the mean (P < 0.001) and the peak (P < 0.001) flow rate increased significantly with increasing numbers of ML. The average (SD) mean flows in the 3 groups were 725 (256), 819 (245), and 833 (323) g/min, respectively, whereas the corresponding values for the peak flow were 1071 (308), 1158 (253), and 1243 (346) g/min, respectively.
Effect on Udder Health
The average monthly bulk SCC of the whole herd was 144,000 and 154,000 cells/ml during the first and second years, respectively. Mean (SD) UDS during yr 1 were 2.0 (2.1), 1.6 (2.1), and 1.6 (2.0) for AMS, FSB, and TSB, respectively. The corresponding means for yr 2 were 1.4 (1.7), 1.4 (2.1), and 1.7 (2.2), respectively. The cow SCC and UDS were numerically, but not significantly, higher in cows with ML compared with cows without ML (Table 5
). The number of cow-days with ML increased significantly (P < 0.001) when the UDS increased from score 0 to 4, but the incidence of ML varied markedly when scores were above 4 (Table 7). The number of cows treated for clinical mastitis was too small to evaluate the effect of ML on the risk of clinical mastitis.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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When including all cows, daily milk production, parity, and month of lactation did not differ significantly between cows with or without ML. However, the number of primiparous cows with ML was more than 6 times higher in AMS than in CMS, whereas the proportion of multiparous cows with ML in AMS was just over double that found in CMS. More than half of the observations of ML made in AMS occurred in primiparous cows. The reason for the high proportion of primiparous cows with ML in AMS is not clear, but it was not due to a larger proportion of missed or incomplete milkings than in multiparous cows. However, social dominance might be a factor of importance. Primiparous cows are often ranked lower than older cows (Dickson et al., 1970), and low-ranking cows have to wait longer for their turn to get access to the milking unit in AMS (Ketelaar-de Lauwere et al., 1996). Stefanowska et al. (1995) observed ML in some cows that had to wait to get access to the AMU. Preliminary data (K. Svennersten-Sjaunja, personal communication) from a parallel study indicate that low-ranking cows in the AMS had higher oxytocin concentrations and spent more time close to the milking unit. Moreover, those cows had more observations of ML than high-ranking cows (K. Svennersten-Sjaunja, unpublished data). Milk leakage was mainly observed when cows were lying down, but it is not known if social dominance can influence lying behavior. However, a long milking interval can result in a shorter time lying during the hours before milking, probably due to the discomfort when lying on a full udder (Österman and Redbo, 2001).
It was 3 times more common that cows in AMS leaked milk 3 times, indicating a more persistent problem in these cows. Parity was not an explanatory factor for this finding because the proportions of primiparous and multiparous cows with multiple ML were similar. However, problems related to the previous milking were probably of importance. Missed or incomplete milking was registered in association with a large number of ML observations, and in almost 60% of the affected cows. However, in several cases, ML did not occur in the same quarter registered to have a problem at milking. Milk leakage was also a common finding when missed milking was simulated experimentally (Stefanowska et al., 2000).
Milk leakage occurred most often in the rear quarters and when cows were lying. The proportions of cows ruminating or resting/sleeping when lying were similar, indicating that this did not influence the occurrence of leakage, even though an increased release of oxytocin has been observed during stimulation of the oral cavity (Svennersten et al., 1990). The increased pressure from the hind legs on the rear part of the udder when lying could explain these findings. This is also consistent with the higher risk of udder infections and mastitis in rear quarters (Adkinson et al., 1993; Lancelot et al., 1997). Proportions of cows lying and standing at the observations did not differ among the barns, indicating that this was not an explanatory factor for the higher ML number in AMS. No influence of estrus on ML was observed. Such relationships might have been expected because inhibition of the oxytocin release and milk let down can occur at estrus, increasing the risk for incomplete milking (Wellnitz and Bruckmaier, 2000).
In CMS, ML was mainly observed at a few of the observation points, whereas the ML in AMS occurred at all times. The time between a specific ML observation and the previous milking varied in AMS. Many (26 and 19% for yr 1 and 2, respectively) of the ML observations occurred 4 h after milking. Almost half of those occasions were explained by missed or incomplete milking of one or several quarters at the previous milking. Such problems were also associated with one-third of the ML observations occurring 4 to 8 h after milking. In 15% of the ML observations, the time from the previous milking was >12 h, indicating that cow traffic was suboptimal. Long milking intervals can be a result of social dominance because low-ranked cows might have to wait longer to the next milking than high-ranked cows for their turn at the AMU (Ketelaar-de Lauwere et al., 1996). In this study, time from milking to ML observation did not differ between primiparous and multiparous cows. A cow’s motivation to be milked and/or fed is another important factor, which is of importance for the length of the milking interval in AMS.
The milk flow rate of a quarter is influenced by teat canal anatomy (Hamann and Dodd, 1992) and can be considered an indirect indicator of the patency of the teat canal. Both the mean and the peak milk flow rate were significantly higher in quarters with ML than in quarters without ML, and increased with increasing numbers of ML per quarter. The research farm at Kungsängen is run as one breeding unit, and the cows are randomly selected to the different barns. It is therefore not likely that the cows’ milk flow rates were different in the AMS than in the other systems. Thus, cow differences among the barns in milk flow rate could not explain the higher incidence of ML in the AMS.
Quarters with high milk flow rates have been associated with an increased risk of infections and mastitis (Dodd and Neave, 1951; Slettbakk et al., 1990; Grindal and Hillerton, 1991; Grindal et al., 1991; Lacy-Hulbert and Hillerton 1995), and ML has been reported to be an important risk factor for clinical and subclinical mastitis (e.g., Jørstad et al., 1989; Schukken et al., 1990; Elbers et al., 1998; Waage et al., 1998). In the present study, the SCC and UDS were numerically, but not significantly, higher in cows with ML. Thus, there was no clear relationship between ML and udder health. Although the observed positive association between the occurrence of ML and an increase in UDS from 0 to 4 could indicate that ML may increase the risk for new infections, no such relationship was observed between ML and UDS higher than 4. The risk of udder infections in association with ML increases when the hygiene in the cows’ environment, especially in the bedding, is poor (Schukken et al., 1990, 1991). In the research farm studied, udder health and hygiene was very good, which probably explained the small effect on SCC and the low number of clinical mastitis cases.
The high occurrence of ML in AMS can to some extent be explained by problems related to disturbances at milking or overly long milking intervals, indicating technical or management problems. However, as mentioned previously, these problems can only explain a part of the ML observations. Milk leakage can occur when the milk let down reflex is activated due to oxytocin secretion. The reflex is normally activated by stimulation of the teats and udder before milking by the milker. However, visual or auditory stimuli of the calf or of the milking process (Peeter et al., 1973; Pollock and Hurnik 1978) can also activate the reflex. In AMS, the cows get more or less constant visual and/or auditory stimuli from the AMU, which could stimulate oxytocin release and milk let down. This, in combination with a higher milk flow in certain quarters may be one explanation to the increased risk of ML in the AMS. However, more studies are needed to investigate the relevance of this hypothesis. Moreover, the effect of social dominance, especially in primiparous cows, and of quarter milking, milking frequency, and the level at cluster take-off on the occurrence of ML in AMS are other factors that need to be studied. The present study was performed during a limited period during the indoor season on a research farm in which the degree of activity was different from that of commercial farms. It is not known if season and activity can influence the occurrence of ML. Preliminary data (our unpublished results) indicate that less ML occurs during weekends compared with weekdays, when more activity is ongoing in the barns. Thus, further studies are also needed on the effect of season and on the occurrence of ML in commercial AMS dairy farms.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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4 h after milking, and half of those were associated with missed or incomplete milkings. Moreover, milk flow rates were higher in quarters leaking milk. More studies are needed on the etiology of ML and on the occurrence and possible effects on udder health of ML in commercial farms.
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Received for publication February 7, 2003. Accepted for publication July 24, 2003.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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