The average number of aggressive interactions was 2.2 per cowrh after milking and Ž
. 2.6 per cowrh after omitted milking
difference not statistically significant . The number of aggressive interactions was not related to the milking order or to the lactation
number. The proportion of numbers of being the aggressor to the sum of being the aggressor and of being the recipient of the aggression was similar after milking and after
Ž .
omitted milking r s q0.86, P - 0.01 . Analysis of where the 468 aggressive interac-
s
Ž .
tions 337 of milked cows and 131 of cows after omitted milking took place revealed Ž
. that cows were most aggressive at the forage feeders 43.4 of cases and the water
Ž .
trough 28.0 of cases . Aggressive interactions also took place, but less, in the feeding Ž
. Ž
. Ž
area 13.5 of cases , around the salt block 7.0 of cases and in the lying area 6.6 .
Ž of cases . Pushing a cow away from her lying place happened exceptionally seven
.
2
cases, 1.5 of all . The x test revealed no difference in the distribution of the location
of the aggressive acts of milked and unmilked cows. Milk leakage from the udder was observed in 60 of cases after omitted milking. In
Ž 5 out of 12 cows milk leakage was always observed after omitted milking e.g., for four
. Ž
occasions of omitted milking , in three cows it was never observed e.g., during any of .
four occasions ; milk leakage was observed irregularly in the remaining four cows after omitted milking. No relation was found between milk leakage after omitted milking and
behaviour after omitted milking or milk yield.
4. Discussion
4.1. Experiences of cows induced by omitted milking It was assumed that cows perceive a mismatch between the familiar daily routine
Ž .
coming to milking parlour, preparation of the udder, milking and the outcome of the Ž
. visit no milking . There would have been physical sensations too: during preparation
for milking the oxytocine reflex stimulates inflow of milk into the cistern of the udder, and therefore if no milking follows, the udder is likely to become distended. Incidences
of leakage of milk observed after omitted milking were also registered in previous research in some cows that were brought in groups to the milking robot but had to wait
Ž .
their turn Stefanowska et al., 1995 as well as in cows waiting for access to a traditional milking parlour. The leakage is a consequence of milk accumulating in the cistern of the
udder and is reinforced by preparation for milking not followed by milking. Cows differ in the occurrence of milk leakage, depending on differences in milk yield, individual
reactivity and, last but not least, the difference in the functioning of the small sphincter muscles closing the milk canals of teats. It was assumed that omitted milking was
experienced by cows externally as an unexpected situation and internally as pressure or at least as the lack of the familiar feeling of a milked-off udder.
It is striking that during the observations the cows whose milking had been omitted urinated twice as often and earlier than milked cows. This difference was highly
significant, even though the cows certainly also eliminated in the return alley, where their behaviour was not observed. This is similar to the finding of a study on cows who
were not selected for milking until they were in the milking stall with a robot: cows after milking failure or a no-milking visit urinated more often in the exit area from milking
Ž .
stalls than milked cows Stefanowska et al., 1999a . Furthermore, in three trials on the behaviour of cows subjected to ‘‘walk-through’’ selection on their way to a milking
robot, it was observed that cows refused access to the robot urinated in the passage with ‘‘walk-through’’ selection more frequently than cows for whom the gate to the milking
Ž .
stalls with robot had opened Stefanowska et al., 1999b . The urination was presumably Ž
. the cows’ response to the uncertainty about their situation. Hopster 1998 reported the
occurrence of elimination by cows exposed to a new environment, but did not distin- Ž
. guish between urination and defecation. Marchal et al. 1995 observed a decrease in
elimination by cows after habituation to an automatic milking system. The empirical observations of farmers are that elimination increases after the installation of a new
Ž .
milking parlour. Kilgour and Albright 1971 suggested that stress stimulated cows to defecate and urinate. It is not known why in the present trial as well as in earlier trials
Ž .
Ž .
reported by Stefanowska et al. 1999a,b the given situation with stress factor had more impact on urination than on defecation.
Another noteworthy result was that cows that came to the milking parlour in the first batch and were subjected to omitted milking stood significantly longer in the cubicles
and lay significantly shorter than milked cows during the following period of 1 h. It seems probable that because they were more motivated for milking they experienced
Ž more disruption. Moreover, because they had a somewhat higher milk yield 26.0 kg of
milkrday in comparison to 23.2 kg of milkrday for cows that were more frequently in .
the second batch they experienced more discomfort than cows from the second batch. Ž
. Ipema et al. 1988 reported that high yielding cows stood longer in cubicles than low
yielding cows and that after introduction of more frequent milking they began to lie longer in the cubicles. The cows that were present most frequently in the first batch were
four cows in second lactation and two cows in first lactation. They were also in the first batch during the third visit to the milking parlour for milking the three unmilked cows.
This suggests that a cow’s motivation to lead the way to the milking parlour may be related to milk yield, age, but maybe also to individual attribute.
4.2. Does omitted milking stress the cow? The question arises whether we can qualify the experience of omitted milking as
Ž .
stress. Hopster 1998 defined stress as a state when the expectations or objectives of an Ž
. animal do not match the observed and sensed environment
external or internal . Unspecific reactions to stressors take place when influencing factors may exert effect on
Ž . Ž
. psychological status uncertainty, fear
Hopster, 1998 . In this context we may hypothe- sise that urination after omitted milking is an unspecific reaction to the disturbance of
Ž .
daily routine e.g., omitted milking . During stress, the concentration of adrenalin and noradrenalin in the blood and also locally released noradrenalin inhibit milk removal
Ž .
Ž .
Hamann, 1994 . Algers 1998 is convinced that stress can affect milk production, but it is difficult to state whether such effects are direct or indirect. In our trial, cows after
omitted milking gave 0.7 kg milk more during the milking 1 h later than cows normally Ž
. Ž
. milked P - 0.01 . This difference can be attributed to the additional third preparation
of the udder and to the extra hour elapsed before milking. During the next morning cows Ž
. after omitted milking gave 1.1 kg milk less than cows normally milked P - 0.01 . This
can be attributed to the 1 h shorter milking interval. However, the difference of 0.4 kg Ž
. milk less P - 0.05 on days with omitted milking than on days without omitted milking
might be caused by the milk ejection process being interrupted during days with omitted Ž
. milking; this agrees with the findings of Bruckmaier and Blum 1998 on oxytocine
release and milk removal in ruminants. It is clear that omitted milking did not influence either the time spent in the forage
installation or the amount of forage eaten. All cows ate intensively during the 1 h after returning from the milking parlour. During that hour they ate on average 1.9 kg of dry
matter from the mixed ration. Compare this with a daily intake of circa 20 kg of dry matter from forage and concentrate as registered in the same installation during another
Ž .
trial Metz-Stefanowska et al., 1993 . The rate of eating of the mixed ration was circa 100 g dmrmin. This is higher than the mean daily forage eating rate of 83 g dmrmin as
Ž .
reported by Metz-Stefanowska et al. 1993 , probably because eating intensity depends on kind of forage and way of rationing and it varies throughout the day. Metz-
Ž .
Stefanowska et al. 1992, 1993 described that after milking in a traditional milking Ž
parlour and also after robotic milking, cows were at the feeding rack optionally
. automatic feeding installation much more frequently than during any other time. Tyler
Ž .
et al. 1997 observed that when forage was available, cows stayed in the feeding area after milking longer than when no forage was available.
It is interesting that the number of aggressive acts and the individual proportion of being aggressorrrecipient was not influenced by omitted milking either. The average
number of 30 aggressive acts within the group during the 1 h of observations agrees Ž
. with observations of Metz 1983 on aggressive interactions between 14 cows provided
with a feeding rack with 7 places and fed ad libitum. According to Metz, the described situation was not as competitive as it can be in case of not feeding ad libitum. Omitted
milking was not a situation that changed aggression beyond an established level in a group.
4.3. Relating the results of research on omitted milking to robotic milking failures In other research conducted in circumstances of automatic milking, cows returned to
Ž .
the AMS after milking failure earlier than milked cows Stefanowska et al., 1999a,b . Compared with the other cows they returned to the AMS without lying or eating more
Ž .
often Ketelaar-de Lauwere et al., 2000 . The cows with recurrent milking failure because their udder conformation was less suitable for robot attachment could develop
their own strategy to try to resolve their situation by returning, with whatever motivation Ž
. to eat concentrate andror to be milked . This was not the case in our trial: during the
third visit to the milking parlour the unmilked cows did not break with the established milking order. It is widely accepted that cows that undergo daily routine as a group react
Ž .
to stress more passively Hopster, 1998 . After failure of cluster attachment, the cows in Ž
. our earlier trials
Stefanowska et al., 1999a,b undertook action: they came back.
However, the experiences of these cows after milking failure of a robot should not be underestimated. After repeated failures they wandered around, which negatively influ-
Ž .
enced their time budget idle time at the expense of eating or lying . Efficient use of time budget is very important for high yielding cows because they must eat and lie a lot.
These cows urinated in the exit area of the AMS more often than milked cows Ž
. Stefanowska et al., 1999a .
In the case of a cowshed with a robot and animals given access to the pasture dependent on milking status, cows may be denied access to outdoors after milking
failure of the robot. They may pay many unsuccessful visits to the robot before finally being allowed outdoors, mostly after the farmer has intervened. It is essential to
establish some time limits for human intervention in the case of milking failure, especially for high yielding cows and when successful milking is a prerequisite for being
Ž allowed to leave the barn or during the periods of longer absence of the farmer e.g., at
. night . It would be possible to estimate the well-being of cows after the failure of the
robot attachment on the basis of their activities following the failure by looking at their idle time and occurrence of urination.
The leakage of milk observed after omitted milking as well as after cluster attachment failure during robotic milking forms a risk for the udder health of cows. Elbers et al.
Ž .
1998 reported that leakage of milk from the udder is one of the factors associated with clinical mastitis at herd level.
5. Conclusions
