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Effects of Mixing on Drinking and Competitive Behavior of Dairy Calves

Animal Welfare Program, Faculty of Land and Food Systems, University of British Columbia, Vancouver, Canada V6T 1Z4

² Corresponding author: nina{at}interchange.ubc.ca

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 
Group housing provides increased access to space and social interactions for calves while reducing labor costs for producers. However, group housing necessarily requires that calves be mixed and no research to date has addressed the effects of mixing on behavior of milk-fed dairy calves. The objective of this study was to monitor the feeding and competitive behavior of individual dairy calves (n = 8) after introduction into an established group of older calves fed ad libitum by a computer-controlled milk feeder. Milk feeding was monitored for 2 d before introduction into the new group and both milk feeding and competitive behaviors were monitored for 4 d after mixing. Mean (± SE) milk consumption before mixing was 9.7 ± 0.7 kg/d, dropped slightly on the day of mixing to 8.6 ± 0.6 kg/d, but increased on d 1 to 3 after mixing to 11.1 ± 0.3 kg/d. Calves visited the feeder less frequently on the day of mixing (6.0 ± 1.8 visits/d) than on either the days before mixing (20.3 ± 2.5 visits/d) or the days after mixing (25.3 ± 6.9 visits/ d). The mean duration of feeder visits and mean milk consumption per visit increased from 4 min 15 s ± 21 s and 0.53 ± 0.06 kg per visit before mixing to 8 min 17 s ± 1 min 28 s and 1.87 ± 0.51 kg per visit on the day of mixing. Competitive displacements from the milk-feeding stall were rare. In summary, feeding behavior of young calves is altered on the day of mixing, but calves are able to maintain milk intake when using a milk feeder fitted with a stall that prevents calves from displacing one another.

Key Words: dairy calf • competition • milk-feeding behavior • regrouping

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 
Group rearing of milk-fed dairy calves is thought to provide advantages in terms of labor but it creates challenges in terms of calf management (Kung et al., 1997). For example, calves in groups may need to compete with group mates for access to key resources including milk. In a recent study, we found that group-housed calves frequently compete for access to milk teats, especially when the teat-to-calf ratio declines (von Keyserlingk et al., 2004).

Changes in social environments can have pronounced effects on the physiology and behavior of animals (Zelena et al., 1999). Competitive interactions generally peak when new animals are introduced into a group, resulting in increased social stress and reduced feed intake (Boe and Faerevik, 2003). Milk-fed calves in groups are often kept in dynamic groups, with new calves introduced soon after birth and older calves removed at weaning (Jensen, 2003), resulting in considerable variation in calf age within the group. Studies on other farm animals have shown that problems related to social integration are normally greater for the introduced animal than for the resident ones (Mench et al., 1990), and that younger animals are more frequently displaced from the feed source than are older individuals (Onsrud, 1999). Recent studies with growing-finishing pigs showed that the feeding behavior of the small pigs is altered in more competitive environments; namely, they consumed a larger proportion of their daily feed intake during the nighttime hours than during the day compared with pigs in a less competitive situation (Georgsson and Svendsen, 2002).

One convenient way of feeding milk to group-housed calves is using computer-controlled nipple feeding systems (Hepola, 2003), but no work to date has examined the effects of mixing on calves introduced into a new group. The objective of this study was to investigate the effect of mixing on feeding and competitive behavior of young calves following introduction into a group pen when using a computer-controlled milk feeding system. We predicted that calves introduced into a preformed group of older animals would experience an increased frequency of displacements and disturbances from the feeder by older calves, leading to disrupted feeding behavior and reduced milk intake.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 
Animals, Housing, and Management
This study was carried out at the University of British Columbia Dairy Education and Research Center in Agassiz (BC, Canada). All animals were cared for according to the guidelines outlined by the Canadian Council on Animal Care (1993). Holstein (n = 8; 7 female and 1 male) calves were separated from their mothers within 24 h of birth and moved to individual pens (1.2 x 1.7 m) with milk supplied from an artificial teat (Milk-Flow Peach teats, Skellerup Industries, Ltd., Christchurch, NZ) positioned at right angles to the wall at a height of 0.6 m.

At approximately 11 d of age (11.25 ± 2.12 d) calves were moved to an individual training pen, measuring 1.2 x 1.8 m, with solid wooden walls 1.2 m high. The computer-controlled milk feeder (DeLaval CF150, De-Laval, Tumba, Sweden) was positioned between the individual training pen and the group pen (5.3 x 1.8 x 1.2 m). All calves were fed whole milk, including milk from cows in the withdrawal period following antibiotic treatment. The amount of the milk from withdrawal cows varied across the experiment depending upon the number of cows being treated. Milk composition was tested monthly by British Columbia Dairy Herd Improvement Services (Chilliwack, BC, Canada). Composition averaged 12.1 ± 0.1% DM and (DM basis) 28.0 ± 0.1% fat, 26.9 ± 0.1% protein, and 45.1 ± 0.0% lactose. All calves had ad libitum access to a 21.6% CP barley-based calf starter (Unifeed Ltd., Chilliwack, BC, Canada), and to water from a bowl, but intake of starter and water were not monitored. Fecal scores were recorded daily for each calf according to Larson et al. (1977).

Experimental Procedure
Each calf was housed in the training pen for 7 d (–7 to –1 d of the experiment). From d –7 to –4 inclusive, calves were provided with ad libitum access to milk through a single teat identical to that described earlier. On d –3 to –1, calves were trained to use a computer-controlled milk feeder. All experimental calves were fitted with a passive transponder encased in a plastic ear tag (All Flex, Inc., Dallas, TX) and attached to the left ear. When a calf placed its head within 25 cm of the milk-feeding station, the calf’s identification number was transmitted to the reader panel. Access to milk was provided through a teat attached to a peristaltic pump that provided milk at a rate of 8 g/s when the calf’s nose was pressed against a metal switch positioned directly behind the teat. Milk was stored in a covered plastic bucket and mechanically agitated for 2 s every 5 min. Milk was warmed by passing through copper coiling in a 37°C water bath before delivery to the calf. All milk-feeding equipment was cleaned at 0700 and 1800 h before adding fresh milk to the reservoir. The milk feeder was calibrated weekly, as per the manufacturer’s instructions (DeLaval, 2003).

Milk Consumption and Behavioral Recording
Milk consumption and feeding patterns for each focal calf (calf under observation) were monitored in the training pen for 48 h immediately before mixing (premixing period), and milk consumption, feeding, and competitive behaviors were monitored for the 24 h after mixing (mixing day) and the subsequent 72 h (postmixing period). Each focal calf was introduced into a different group of 3 nonexperimental calves (approximately 4, 5, and 6 wk of age).

Measuring Milk Intake.
Milk intake was recorded by the feeder every 24 h. Feeding behavior was monitored using video cameras connected to a multiplexer and a time-lapse videocassette recorder. One camera was positioned 1.2 m directly above the entrance to the feeder, and the other was positioned 1.2 m above and 0.9 m in front of the entrance to the feeder. Tapes were recorded in 72-h mode and scored continuously for visits to the feeder and competitive interactions. A feeder visit was defined as occurring when a calf was positioned so that it was standing with its head facing the machine, and shoulders beyond the entrance to the stall leading to the milk feeder.

Measuring Aggressive Behavior.
Competitive behaviors were scored only during feeder visits and included contacts and displacements. A contact was scored when either the head or shoulders of a calf outside the stall touched any part of the body of the calf inside the stall. A displacement was scored if a calf vacated the stall immediately following a contact and the contacting calf immediately entered the milk feeder.

Data Analysis
All analyses considered the focal calf as the observational unit. Preliminary graphical analysis revealed that behavior and intake measures were generally similar on the 2 d before mixing, and the 3 d following mixing, but disrupted on the day of mixing. Therefore, responses were averaged for these 3 periods (premixing period, mixing day, and the postmixing period). Behavior and intake on the day of mixing were compared with responses during the adjacent periods using paired t-tests. The log₁₀-frequency distribution of the interval lengths between these feeder visits for each individual calf for d –2 to 3 was used to determine the meal bout criterion, following von Keyserlingk et al. (2004). However, no clear distributions could be identified so no meal criterion was established. Thus, for the purpose of this paper, each individual visit to the feeder was defined as a meal.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 
Calves consumed on average more than 10 kg of milk per day both before and after mixing, but consumption declined by approximately 20% on the day that calves were mixed (Table 1). More dramatically, the number of meals that calves consumed declined by more than 50% on the day of mixing. However, calves appeared to compensate for the reduced meal number at mixing by more than doubling their average intake per meal on this day. These larger intakes were achieved in part by increased meal duration (from just over 6 min to just under 12 min per meal). Calves also increased their intake rate from approximately 9 kg/h before mixing to 14 kg/h on the day of mixing. However, unlike the other measures of feeding behavior, intake rate also remained high during the days after calves were mixed. Overall, calves spent less time on the teat at mixing compared with either before or after mixing. This decline occurred especially in the 3 h following introduction into the new group (i.e., 1400 to 1700 h on Figure 1). The 24-h distribution of visits to the feeder on other days was relatively uniform.

View larger version (16K): [in this window] [in a new window]   Figure 1. The total number visits to the feeder by all calves (n = 8) on d 0 and the mean of d 1 to 3 in relation to time of day. Columns represent the number of visits in the hour up to that time. The x-axis begins at 1400 h, as the calves were mixed at 1400 h on d 0. Treatment means ± SEM are provided in Table 1.

Milk consumption in the present study was within the range previously reported for calves of this age fed milk ad libitum by teat (Chua et al., 2002; Jasper and Weary, 2002) and for those fed ad libitum using a computerized milk feeder (Jensen, 2003). There was a decline in intake on the day of mixing when calves were moved to the group-housed pen, but intakes increased on the days after mixing.

In a recent study, von Keyserlingk et al. (2004) found that calves drank less milk when competition for teats increased. This reduction in intake was likely mediated by increased competitive behavior, and specifically by increased displacements from the teats. Although we observed decreased intakes on the day of mixing, we did not see a prolonged decline in intake. Hyun et al. (1998) reported that mixing had no effect on daily feed intake when pigs were fed using an individual feed intake recording system that enabled only one pig to feed at a time. Likely the presence of the milk-feeding stall in the current study provided some protection to the calves during milk-feeding events as evidenced by the low number of aggressive interactions observed throughout the study. Jensen and Holm (2003) and Weber and Wechsler (2001) reported considerably more displacements per day in their study. However, they had 8 and 15 calves in each group, respectively, compared with our groups of 4. Thus, future research should examine the effects of mixing into larger groups of calves.

The time spent on the teat in the present study was similar to the amount of times calves spend suckling their dams (about 1 h/d; Day et al., 1987), indicating that calves fed milk from artificial teats exhibit a similar motivation to suck. Teat-based systems allow calves to perform natural sucking behavior (Hammell et al., 1988), likely increasing the secretion of the digestive hormones insulin and cholecystokinin (de Passillé et al., 1992; Lupoli et al., 2001).

There was no clear pattern in the frequency distribution of the intervals between feeder visits, thus preventing an objective definition of a meal criterion (DeVries et al., 2003; von Keyserlingk et al., 2004). The lack of any clear pattern may be attributed to the type of milk delivery system used in this study. The automatic milk-feeding unit delivered warm milk to calves at every visit to the feeder. In previous studies (Appleby et al., 2001; von Keyserlingk et al., 2004), milk was warm only immediately after delivery of fresh milk to the feeder in the morning and evening. These previous studies also provided no milk-feeding stall to protect calves from displacements while sucking, likely increasing the number of short intervals between visits as described by von Keyserlingk et al. (2004).

Although the number of meals consumed by calves before and after mixing was similar to that previously reported by von Keyserlingk et al. (2004), meal number was reduced by 67% on the day of mixing. Interestingly, calves appeared to compensate for the reduced number of meals on the day of mixing by increasing both meal duration (44%) and average meal size (64%), resulting in only a modest overall decline in milk intake. Similar compensatory behaviors were reported by Hyun et al. (1998) who found that although mixing tended to cause pigs to decrease the number of visits to the feeder, they tended to increase the duration of each visit such that daily intake was maintained. Although the pigs adjusted their feeding behavior for 4 to 5 d after mixing before returning to baseline levels (Hyun et al., 1998), the calves in the present study were able to reestablish their premixing feeding patterns after just 1 d. This difference may be because pigs generally show more overt signs of aggression following mixing (Stookey and Gonyou, 1994), and might require longer to establish a stable social hierarchy. Calves and older cattle in nature rarely compete for resources (von Keyserlingk et al., 2004) and thus, may prefer to adjust their behavior in ways that prevent physical contact with other calves.

Unlike the findings of Appleby et al. (2001), who showed that teat-fed calves fed individually consumed their largest meal just after the delivery of fresh milk, our results show that the calves appeared to distribute their visits to the feeder throughout the day. Again, this may be explained by the fact that calves in this study were provided milk at a constant temperature throughout the day. When housed in larger groups of 20 calves, and fed from a single milk feeder, some calves do preferentially feed at night (Babu et al., 2004), likely due to competition during peak feeding times. In the current study, calves were rarely seen to wait to gain access to the milk feeder. Morita et al. (1999) housed calves in a group of 26 and noted that some calves waited for up to 60 min to access the feeder.

	CONCLUSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 
For small groups of calves fed from a computerized feeder, mixing young calves has only transitory effects on feeding behavior. On the day of mixing, calves visit the feeder less frequently, but compensate by increasing the duration and amount of milk consumed per meal. More research is required to understand the effects of mixing when keeping calves in larger groups.

	ACKNOWLEDGEMENTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 
We thank the staff and students at the University of British Columbia’s Dairy Education and Research Center. We especially thank Danica Olenick, Lizanne Steunenberg, Timothy Leung, and Nelson Dinn for their help in running this experiment. We are also grateful to Doug Veira for his help and support throughout the project. General support for the Animal Welfare Program is provided by the Natural Sciences and Engineering Research Council through the Industrial Research Chair in Animal Welfare, and by contributions from the Dairy Farmers of Canada, the BC Dairy Foundation, the BC SPCA, members of the BC Veterinary Medical Association and many others listed at www.landfood.ubc.ca/animalwelfare.

	FOOTNOTES

 
¹ Current address: Teagasc, Moorepark, Fermoy, Cork, Ireland.

Received for publication March 31, 2005. Accepted for publication September 8, 2005.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSION ACKNOWLEDGEMENTS REFERENCES

 


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