J. Anim Sci. 2007. 85:1522-1529. doi:10.2527/jas.2006-813
© 2007 American Society of Animal Science
Reaction of foster cows to prevention of suckling from and separation from four calves simultaneously or in two steps1
J. M. Loberg*,2,
C. E. Hernandez*,
T. Thierfelder
,
M. B. Jensen
,
C. Berg
and
L. Lidfors*
* Department of Animal Environment and Health, Swedish University of Agricultural Science, Skara, Sweden;
and
Department of Biometry and Engineering, Swedish University of Agricultural Sciences, Uppsala, Sweden;
and
Department of Animal Health, Welfare and Nutrition, Research Centre Foulum, Tjele, Denmark; and
and
Swedish Animal Welfare Agency, Skara, Sweden
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Abstract
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The aim of this study was to investigate if a 2-step method of preventing suckling and cow-calf separation reduces the stress reaction in foster cows compared with a simultaneous separation method. Seven Swedish Holstein and 5 Swedish Red dairy cows were used as foster cows, each having a group of 4 calves. The foster cow-calf group was formed when calves were 1 wk old, and the calves were prevented from suckling at 10 wk of age. In 6 of the cow-calf groups, calves were prevented from suckling by simultaneous separation from the cow (control). In the other 6 groups, calves were fitted with a nose-flap, which prevented them from suckling while they were kept together with the cow for another 2 wk before they were separated (2-step). The behavior of the foster cows was observed at 4 observation periods, 0 to 2, 8.5 to 9.5, 24 to 26, and 72 to 74 h after the calves were prevented from suckling (2-step), after separation (2-step), and after calves were prevented from suckling by simultaneous separation (control). For both treatments, saliva cortisol was sampled once daily for 5 d at wk 10. This was repeated at wk 12 for the 2-step treatment. Heart rate was measured with the behavioral observations. Control foster cows vocalized more (P < 0.001) and walked more (P = 0.005) than the 2-step foster cows after prevention of suckling and after separation from the calves. When control cows were separated from their calves, they more frequently (P < 0.001) held their head out of the pen than was the case with 2-step cows when separated 2 wk after prevention of suckling. The variation in heart rate was larger in the control group compared with 2-step cows at 0 to 2 h after separation/prevention of suckling (P = 0.002). No effect of treatment was found on cortisol concentration. Our conclusion is that separating the 2 events "prevention of suckling" and "separation" reduces the stress experienced by the foster cow at weaning.
Key Words: behavior • cortisol • foster cow • heart rate • stress • weaning
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INTRODUCTION
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Dairy cows may be used as foster cows (i.e., taken out of production and given 3 to 6 alien calves to nurse during the whole milk period of the calves). In this way, calves are raised under more natural conditions, and in better correspondence with regulations for ecological farming (KRAV, 2006
). However, there are observations indicating that foster cows form a strong bond to 1 or more of the calves, resulting in behavioral reactions at the time of weaning (L. Lidfors, unpublished data; Nielsen, 2005).
Weaning has been described as "a normal stage in the transition to independent adulthood" (Stookey et al., 1997), or more restrictively, when the offspring stops suckling and begins eating solid food (Martin, 1984). During natural weaning, the cow terminates the suckling bouts more often and sometimes refuses to be suckled (Walther, 1984), but the calf still has the possibility of social contact with the dam. The reaction to abrupt weaning between mother and calf in beef cattle is well documented (Lefcourt and Elsasser, 1995; Stookey et al., 1997). Studies investigating how to wean beef calves in a more "natural" way with fence line contact (Stookey et al., 1997; Price et al., 2003) or with a nose-flap to prevent suckling (Haley et al., 2001, 2005) have shown that mother and calf showed fewer behavioral signs of stress when they had the opportunity to have physical contact. In relation to the natural weaning age (8 to 11 mo, Bos indicus; Reinhardt and Reinhardt, 1981), calves in beef production are weaned closer to that age (6 to 9 mo; European Commission, 2000) compared with calves in dairy production (2 to 3 mo). Therefore a method to reduce the stress at weaning in beef cattle might be less efficient when applied very early in the suckling period in dairy cattle.
The aim of this study was to investigate if prevention of suckling and separation from the calves in 2 steps would reduce stress-related reactions in the foster cows after 2.5 mo of suckling in a dairy production system.
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MATERIALS AND METHODS
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Animals and Housing
Experimental procedures used in this study were approved by the Research Animal Ethics Committee (Swedish Animal Welfare Agency). The study was conducted on a dairy farm in the southwest of Sweden that produces milk according to Swedish regulations for ecological production (EC, 1999; KRAV, 2006). Cows were kept in a cubicle-based loose housing system, with a milking parlor with 2 x 12 places (Fullwood, UK). Calves were housed in an adjacent barn in large groups with several foster cows during their suckling period and in smaller groups after weaning. The farm had 296 cows (Swedish Red, n = 108; Swedish Holstein, n = 188).
During the experiment, foster cows and their foster calves were kept in the same barn as the calves. Each group of 1 cow and 4 calves was kept in a pen of approximately 20 m2 (range 14.4 to 26 m2). The floor was concrete with rubber mats (used for 10 cow-calf groups) and wood shavings. Twelve cows (5 Swedish Red, 7 Swedish Holstein) and 48 calves (16 Swedish Red, 32 Swedish Holstein) were used. Foster cows had been lactating for 11 to 211 d (mean 129 d) when the cow-calf groups were formed. In a previous study on foster cow’s acceptance of the calves, we found no difference between cows that were 4, 7, 30, or 180 d in lactation (Loberg and Lidfors, 2001). All cows had to produce at least 25 L of milk/d to be included. All calves were kept with their own mother during the first week after birth, after which they were moved together with 3 other calves to a pen with a foster cow. The foster cow was tied for the first 12 h and the calves were left to run free, after which the cow was untied and the whole group was filmed for 1 h. During this hour, a person observed the group to detect any aggressive behavior of the cow toward the calves. However, none of the foster cows needed to be replaced due to aggression or for any other reason after this observation. All foster cows accepted suckling by the calves. The cow-calf groups were kept together in the pen for the following 9 wk before any treatment was applied. They were fed a total mixed ration twice a day and had ad libitum access to water in water bowls.
Prevention of Suckling and Separation
In 6 of the cow-calf groups, the calves were prevented from suckling by separation from the foster cow at 10 wk of age (control). In the other 6 groups, the calves were prevented from suckling at 10 wk of age and separated at 12 wk of age (2-step). The calves were prevented from suckling by fitting a plastic device (Quietwean nose-flap, JDA Livestock Innovations, Saskatoon, Canada) in the nostrils, which allowed them to eat and drink. In addition, the cow was fitted with an udder net to prevent the calves from suckling in case any calf should lose its nose-flap. The 2-step calves were kept with the foster cow for another 2 wk before they were separated.
In the 2-step treatment, there were 3 cows from each breed. The control treatment had 4 Swedish Holstein and 2 Swedish Red cows. In 8 of the 12 cow-calf groups, both breeds were represented among the calves; and in the remaining 4 groups, there were only Swedish Holstein calves. Groups from the 2 treatments were balanced between the differently sized pens. At separation, each group of calves was moved to an empty group pen in the same building, at a distance of 4 to 10 m from the original pen. The distance between the original pen and the calf pen was balanced across treatments. The foster cows stayed in the original pen until the observations ended and were able to see and hear their foster calves after separation. All cows were milked in the milking parlor twice a day from the time that the calves were removed or prevented from suckling. When the last observations were finished, the cows were moved to the loose housing area. Because it was not known how the nose-flap would affect initial feed intake and one of the purposes was to compare calf BW gain, calves in the control group were also fitted with a nose flap after separation from the cow.
Behavioral Observations, Cortisol Sampling, and Heart Rate Measurements
The sampling schedule for cows in both treatments is described in Table 1. During all behavioral observations, we observed a focal animal and recorded the frequency per minute of different behaviors by continuous recording. Cows were observed for 1 min every second minute during the observation period. Two persons made simultaneous observations of the cow and the calves in the same group. Before the beginning of the study, the 3 persons involved in the observations practiced together to ensure equivalent definitions of the different behaviors. Results from the observations of the calves will be published in a separate paper.
For saliva sampling, the cow was moved to the feeding trough and locked into the head gate. The person taking the sample held the head in a firm grip and placed a cotton swab (Salivette, Sarstedt, Aktiengesellschaft & Co. Nümbrecht, Germany), which was held with a metal surgical clamp in the mouth of the cow until enough saliva was collected (approximately 1 mL). Saliva samples were centrifuged at 4,500 x g for 15 min immediately after collection and then frozen at –20°C until analysis. The saliva cortisol concentration (µg/dL) was measured using a solid phase RIA (Count-A-Count RIA kit, Diagnostic Products Corp., Los Angeles, CA) following standard procedures. The intraassay CV ranged from 4.0 to 6.6%, and the interassay CV was <10%. The detection limit of the assay was 0.02 µg/dL. The RIA was validated for saliva with a recovery of 101.4% of cortisol that had been added to pig saliva and incubated for 3 h at room temperature.
The heart rate was recorded in beats per minute (bpm) using the Polar Horse XTrainer (Polar Electro Oy, Kempele, Finland), and the 2 electrodes were fitted on the cow with an elastic girth. To facilitate contact between the skin and the electrodes, a gel (Lectro Derm, Swevet Piab, Sjöbo, Sweden) was used. A watch receiver, which stored the measurements from the electrodes, was also attached to the girth on the cow’s back and was set to calculate the heart rate at 15-s intervals. The Polar monitors calculate a value every 15 s that is derived from a moving average using an algorithm. The receiver and the electrodes were covered with a flexible bandage (Horse Guard, Roskilde, Denmark) to prevent the calves in the pen from manipulating the equipment. The data from the receiver was transferred to a computer via a Polar Interface (Polar Electro Oy).
Statistical Analyses
Behavior.
All relationships between behavioral responses and potential predictors were analyzed with log-linked Poisson regression models (PROC GEN-MOD, SAS Inst. Inc., Cary, NC) because behaviors were observed as frequency counts on approximately Poisson-distributed, random variables. As individual cows were being repeatedly observed over equidistant times, quasi-likelihoods were used to estimate first-order, autoregressive correlation structures within the repeated subjects (within observation x cow). Analyses were initiated by inferring the cows’ reactions to the prevention of suckling via the observations during wk 10 for both treatments. The relationship between treatment (2-step or control), observation time (0 to 2, 8.5 to 9.5, 24 to 26, or 72 to 74 h after prevention of suckling, after separation, or both), and breed (Swedish Red or Swedish Holstein) together with the corresponding second degree interactions, and the behaviors vocalizing, walking, lying, eating, ruminating, and sniffing the interior of the pen were examined. The observations during wk 10 for the control cows were analyzed together with wk 12 for 2-step cows, representing the cows’ reactions to separation. The same model as described previously was used for the behaviors walking, lying, eating, ruminating, and sniffing the interior of the pen. When applying this model to the behaviors vocalizing and head outside pen (standing with the head outside of the pen), there were no recordings in some of the resulting factor levels of interaction. Therefore, a simpler model was used, which addressed treatment, observation time, and breed, together with the interaction between treatment and breed.
With the chosen models being relatively well balanced, least squares means provided the best linear-unbiased estimates for the respective models designs (Milliken and Johnson, 1992). The mean values presented were calculated from the estimates produced by SAS. The accompanying prob-values were asymptotically 
2-distributed and should not be too conservatively compared with critical levels of significance. To create coherence between the observed effects and statistical power, prob-value structures reaching 20 to 30% may be considered (Mallows, 1973; McCullagh and Nelder, 1989).
Heart Rate.
All heart rate data collected before the calves were separated or fitted with the nose-flap (between 0915 and 0950, Table 1
) were removed from the data set. This period was used for acclimatization to the equipment for the cows, and therefore the data were not used in the analysis. Errors in the data set were removed by inspection of histograms. With the moving average structure of the Polar monitor being unknown (confidential), interobservational effects could not be considered. Instead, errors were considered as randomly occurring, whereby approximately 1.6% of the data set was removed. With heart rates measured equidistantly every 15th second, strong auto-regression prevailed, with auto-regressive orders varying from one cow to another. To correctly specify the significance of cross-correlative effects, auto-regression was filtered with AR-filters (Box and Jenkins, 1976) using Statistica 7.1 (StatSoft Inc. Tulsa, OK). Before AR-filtering, each heart rate series was characterized with median heart rate and interquartile range. The slope of the heart rate was calculated after a 4253H-filter, whereas the heart rate SD was determined after an AR-filter was applied. The relationship between these heart rate characteristics and treatment, observation time, and breed, together with the corresponding second-degree interactions was examined with ANOVA (GLM, Statistica).
Cortisol.
The effect of treatment on cortisol concentration, increase in cortisol from the beginning value, and difference in cortisol between 2 consecutive samples was examined using PROC GENMOD (SAS) specified with normal distributions and identity link functions. Intracow covariances were addressed with a first-order autoregressive correlation structure. Again, the resulting prob-values were asymptotically 2-distributed.
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RESULTS
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Behavior
Prevention from Suckling.
Cows in the 2-step treatment vocalized less (3 times/h) than cows in the control treatment (26.4 times/h, P < 0.001). There was an interaction between treatment and observation time on the number of recorded vocalizations (Figure 1). Cows in the control treatment vocalized more than the 2-step cows until 26 h after calves were prevented from suckling. There was no difference between the 2 treatments on the fourth day. In both groups, cows vocalized most often during the observation period occurring 8.5 to 9.5 h after the calves were prevented from suckling (Figure 1), but there was a large difference between treatments. Control cows vocalized 10 times more than the 2-step cows. During this observation, observers noted that cows in the 2-step treatment group moved toward the calves and spread their hind legs while vocalizing. Swedish Red cows (18 recordings/h) vocalized more (P < 0.001) than Swedish Holstein cows (4.8 recordings/h).
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Figure 1. Estimated mean number of vocalizations/h for foster cows during the 4 observation periods after prevention from suckling by separation (control, n = 6) or a nose flap (2-step, n = 6). There was a significant difference between the 2 treatments at 0 to 2 (P = 0.001), 8.5 to 9.5 (P < 0.001), and 24 to 26 (P < 0.001) h after prevention of suckling (asymptotically 2-distributed prob-values).
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Control cows (6 recordings/h) walked more (P = 0.005) than the 2-step cows (3 recordings/h). The number of recordings of walking did not differ from the first to the third observation period, but decreased (P = 0.05) from the second (4 recordings/h) to the third observation (2 recordings/h). There was also an interaction between treatment and observation time, where the amount of walking increased from the first to the second observation period in the control group but decreased in the 2-step group (Figure 2).
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Figure 2. Estimated mean number of recordings of walking/h for foster cows during the 4 observation periods after prevention from suckling by separation (control, n = 6) or a nose flap (2-step, n = 6). There was a significant difference between the 2 treatments at 8.5 to 9.5 (P = 0.008) and 24 to 26 (P < 0.001) h after prevention of suckling (asymptotically 2-distributed prob-values).
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The different treatments did not affect the number of recordings of eating, ruminating, or the percentage of observations lying. The number of recordings of sniffing the interior decreased with observation time with the highest number of recordings between 0 and 2 h (12.6 recordings/h) and the lowest between 72 and 74 h after treatment was applied (4.2 recordings/h; P = 0.005).
Separation.
Two-step cows vocalized less at separation compared with control cows (P < 0.001; Table 2). There was also an effect of treatment on walking behavior, where 2-step cows walked less than control cows at separation (P < 0.001; Table 2). Swedish Red cows (4.2 times/h) walked more (P = 0.002) than Swedish Holstein cows (1.8 times/h). The interaction between treatment and observation time for walking was very similar as the interaction shown in Figure 2; but after separation, control cows walked more than the 2-step cows during the first 3 periods (0 to 2: P = 0.026; 8.5 to 9.5: P < 0.001; 24 to 26: P < 0.001; 72 to 74: P = 0.80), until 26 h after separation.
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Table 2. Behaviors of foster cows when calves were prevented from suckling and separated simultaneously (control, n = 6) or separated 2 wk after the calves were prevented from suckling with a nose-flap (2-step, n = 6)1
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Foster cows had more recordings of eating during the first (8.4 recordings/h) and second (10.8 recordings/h) observation period compared with the third (3.6 recordings/h) and fourth (3 recordings/h; P = 0.01). Cows in the 2-step group were lying down more after separation compared with cows in the control group (P < 0.001; Table 2). For lying behavior, the interaction between treatment and observation time showed that the 2-step cows did not decrease time spent lying down after separation from calves, but control cows were lying down less during both the second and third observation periods (P < 0.001; Figure 3). None of the factors included in the model had an effect on number of recordings of rumination in foster cows after separation from their calves.
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Figure 3. Estimated mean percentage of observations of lying down of foster cows during the 4 observation periods after separation from calves simultaneous with the prevention of suckling (control, n = 6) or 2 wk after prevention of suckling (2-step, n = 6). There was a significant difference between the 2 treatments at 8.5 to 9.5 (P < 0.001) and 24 to 26 (P < 0.001) h after separation (asymptotically 2-distributed prob-values).
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The number of recordings of sniffing the interior of the pen decreased with time after separation. Foster cows sniffed the interior and the floor less often during the third (4.2 recordings/h; P = 0.019) and the fourth (3.6 recordings/h; P = 0.027) period compared with the first period (9 recordings/h). Swedish Red cows sniffed (7.8 recordings/h) the interior more (P = 0.001) than Swedish Holstein cows (3.6 recordings/h) after separation. Foster cows that were separated 2 wk after prevention of suckling stood with the head outside the pen less after separation than foster cows that were separated simultaneously as the prevention of suckling (P < 0.001; Table 2). Cows stood with their heads outside the pen more during the second observation (5.4 recordings/h), about 9 h after separation, than on any other observation (1.8, 1.2, and 0.24 recordings/h for observations 1, 3, and 4, respectively; P < 0.001).
Heart Rate and Cortisol
Prevention from Suckling.
There was a treatment x observation time interaction (P = 0.015) for the inter-quartile heart rate range. During the first observation, interquartile heart rate range was greater in the control treatment (8.9 ± 0.53 bpm) than in the 2-step treatment (6.4 ± 0.34 bpm). There was also a larger negative slope of the heart rate curve in the control treatment (–0.35 ± 0.09) compared with the 2-step treatment (–0.03 ± 0.06) for all observations (P = 0.008). The median heart rate was greatest during the second observation, 8.5 to 9.5 h after prevention of suckling (81.5 ± 2.0, 92 ± 1.9, 77.7 ± 1.6, 75.9 ± 1.9, and 77.6 ± 2.0 bpm for observations 1, 2, 3, 4, and 5 respectively; P < 0.001).
Separation.
Median heart rate was greater during the second observation (86.3 ± 2.2 bpm) than during the third (74.9 ± 2.9 bpm), fourth (71.6 ± 2.2 bpm), and fifth (74.1 ± 2.3 bpm) observations (P = 0.002). There were no differences between treatments for salivary cortisol concentration (0.05 ± 0.003 µg/dL), increase in cortisol from the beginning value (0.004 ± 0.007 µg/dL), or difference in cortisol between 2 consecutive samples (0.001 ± 0.005 µg/dL) when considering the reaction to the prevention from suckling or the reaction to separation.
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DISCUSSION
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The behavioral reaction was less for the 2-step cows compared with the control cows. This was true both when comparing the reaction to the prevention of suckling and separation at 10 wk and when comparing the separation at 12 and 10 wk, respectively.
Vocalizations
Control cows had a greater number of recordings of vocalization during the first 26 h, but there was no difference between the 2 treatments after 72 h. In a previous study of beef cattle, the difference in vocal behavior between 2-step weaned cows and control cows lasted for 4 d (Haley, 2006). In beef cattle, the ability of the cow to take care of the calf is important for production, and therefore good maternal traits are highly valued. In dairy cattle, selection has been for high milk production, and the cows are usually not allowed to take care of their calves. This might have led to a lower maternal responsiveness, which could explain the shorter length of reaction to separation in this study. The highest number of recorded vocalizations for the control cows was during the evening observation, about 9 h after separation from the calves. This delay in reaction has previously been found by Weary and Chua (2000) studying separation of dairy cows from their own calf. This increase in vocalizations was also recorded for cows in the 2-step treatment where the calves were still kept with the cow. It was during that observation that the cows moved toward the calves, spread their own hind legs, and vocalized. It appeared as if they were calling for the calves to suckle, although this is only a suggestion. The cows had been milked just before the second observation, so the vocalizing should not be due to udder fill. It has been argued that cattle emit situation-specific calls (Watts and Stookey, 2000, 2001); but because we did not distinguish between different types of calls in this study, we cannot determine if these calls were of a different type or frequency. The 2-step foster cows had a lower number of recorded vocalizations at separation than control cows. This difference in vocal behavior at the time of separation has been found in beef cattle (Haley, 2006) where calves had been prevented from nursing for 5 d or allowed to suckle until separation. In the study by Haley (2006), the rate of vocalizing after separation were 4 times greater for the group that was abruptly weaned and separated, and in our study the rate of vocalizing after separation was 24 times more in the control group. The differences between these 2 studies were that Haley (2006) used the nose-flap during a shorter time period before separation, and the control and 2-step groups were separated at the same time.
Walking
Control cows walked more than 2-step cows when comparing the effect of preventing suckling and the effect of separation. This increase in activity can be a sign of distress and may reflect that the cow was searching for the calf/calves. The increase in activity as a response to separation has previously been found in dairy cattle (Flower and Weary, 2001), horses (Moons et al., 2005), and monkeys (Reite et al., 1981). The increase in vocal behavior and the decrease in walking from observation 1 to 2 in the 2-step cows support the idea that the vocalizations made by these cows 9 h after calves were prevented from suckling were a call for the calves to come and suckle.
Head Outside the Pen
In other studies on separation, the observation that cows and calves stand with their head outside the pen has been interpreted as an attempt to become reunited and has been used as a sign of distress caused by the separation (Flower and Weary, 2001; Stehulová et al., in press). In our study, control cows stood with the head outside the pen more often than the 2-step cows after the calves had been removed, and this adds to our interpretation that the separation of cow and calves in the 2-step group was a less stressful event compared with that experienced by the animals in the control group.
Breed Differences
In this study we included the 2 most common breeds of dairy cows in Sweden, the Swedish Red and the Swedish Holstein. Both breeds have been used as foster cows previously and they accepted foster calves equally well, but the Swedish Red cows sniffed the calves more than the Swedish Holstein cows (Loberg and Lidfors, 2001). In this study, difference in behavior between the breeds was in accordance with the above. The Swedish Red cows sniffed the interior and floor of the pen more after separation from the calves. In addition they vocalized more than the Swedish Holstein cows when calves were prevented from suckling, and they walked more when comparing the effect of separation. This finding indicates that Swedish Red may be affected more by the weaning and separation than the Swedish Holstein cows. This finding, although interesting, should be treated with caution because the sample sizes were small. Differences in maternal behavior between breeds have previously been found in sows (Sinclair et al., 1998) and sheep (Dwyer et al., 1998).
Heart Rate
The greater median heart rate during the second observation period compared with during all other observations could be explained by the greater number of recordings of eating during this period. An increase in heart rate during feeding has previously been reported by Hopster et al. (1995). An increase in activity could also explain an increase in heart rate, but in this study the increase in heart rate was for both treatments; and in the 2-step treatment, cows decreased in activity across the observations. The interquartile range reflects the variation in heart rate, and the slope gives an idea about how much the heart rate increased or decreased in total during the observation. The larger interquartile range in control cows during the first 2 h of observation, in combination with the larger negative slope for all observations, indicates a greater stress response in this group. Use of heart rate measurements to investigate a stress response in an animal is useful but also difficult because there are many factors affecting heart rate that are difficult to control. In future studies, it would be better to be able to have a continuous recording of the behavior to be able to match the heart rate with the behavior.
Cortisol
The abrupt prevention of suckling by separation did not affect salivary cortisol concentration in this study. This lack of response in cortisol concentration was also found by Lefcourt and Elsasser (1995), who measured catecholamine and cortisol release as a response to abrupt weaning in beef cattle. One explanation for this could be that samples were taken after the behavioral observations and that the sampling interval missed the possible peak of cortisol. In a comparison of cortisol in plasma and saliva (Negrão et al., 2004) after ACTH administration in calves or milking in cows, cortisol in plasma and saliva peaked at 40 min after ACTH and at 20 min after milking. After ACTH administration in the calves, the cortisol in plasma and saliva were still higher than baseline after 120 min. The authors pointed out that there were differences in the cortisol measured in saliva and plasma concentrations between individuals, but the relation between plasma and saliva concentrations was consistent. Hernández (2004) showed a peak in saliva cortisol about 30 min after cows had been separated from their calves and tied for the first time. Two hours after the stressful event, the cortisol had returned to baseline level. We do not know how severe the stress was in our study, but our guess is that it was at least as stressful as milking. In that case, the peak in salvia could have occurred between 20 and 40 min after separation from the calves, and it was not possible to restrain the cows 30 min after separation because this would have disturbed the behavioral observations and heart rate measurements.
Foster Cows and Dams
The reaction to separation shown when separating the dam from the calf is caused by the bond that has been established between the 2. There are anecdotes, but only a little empirical evidence (Lidfors, 2000), on the response of foster cows and calves to separation. The reaction observed in this study indicates that there is also a bond formed between the foster cow and her calves. Nielsen (2005) observed the distance between foster cow and each individual calf and the social interactions between foster cows and calves in 11 of the groups in our study and found that 8 foster cows had established a stronger bond to 1 or 2 of the calves, whereas in the rest of the groups no clear preference for any calf was detected. Whether this bond is weaker, or of the same magnitude as, the bond between a mother and her own calf remains to be investigated.
Our conclusion is that the method of separating the 2 events "stop suckling" and "physical separation" by use of a nose-flap reduces the behavioral stress response in foster cows.
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Footnotes
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1 This study was financed by STINT, Formas, and the Swedish Animal Welfare Agency. We thank the staff at Kårtorp farm for their valuable assistance. 
2 Corresponding author: jenny.loberg{at}hmh.slu.se
Received for publication December 13, 2006.
Accepted for publication March 1, 2007.
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Abstract
INTRODUCTION
