Why Do Cows Bunch?
Bunching Check List
- Cows bunch as a reaction to heat stress and fly worry
- Design barns with an East/West orientation and solid end walls
- For bunching due to heat stress, improve cow cooling by darkening the barn and creating a more uniform light intensity by closing the curtains
- Take steps to reduce the fly population if bunching appears to be related to fly control issues
It is not uncommon for some freestall barns to experience cow bunching problems, especially during the hot summer months. Usually around midday, farmers will complain that the cows are all standing bunched together at one end of the freestall pen, leaving large areas of the pen empty.
Cows appear to bunch for two main reasons:
- They are too hot
- They are worried by flies
When cows are heat stressed, it appears that they possess an innate behavioral response that is ‘hardwired’, which tells them to seek out a dark place to ‘cool off’. For grazing animals, seeking shade is a natural response to heat stress at pasture. In a freestall barn, it is common for the cows to bunch in the middle of the barn where it is usually darker and away from the side walls where the sun may be pouring in. Interestingly, the darker area may not be cooler, especially when the group has been bunched there for a while.
Efforts to spread the cows out or trap them will fail. The solution is to improve cow cooling and limit the variability in light intensity within the pen.
To improve cow cooling, it is essential to address the critical control points for heat stress on the farm such as in the milking center holding area. Limiting time and providing sufficient fan capacity in the holding area, having good air flow over the lying area in the pens, and adding soaking systems where needed, can improve cow cooling.
We favor East/West oriented barns to reduce pen exposure to direct sunlight in the afternoon. Light intensity variation can be limited by closing the curtains on the bright side of the barn 80% or by investing in shade blinds that can be pulled down the sidewall. It is important to avoid using transparent siding on the ends of the barn as this will let more light in during the summer and increase the variability in light intensity throughout the pen.
These shades decreased the glare of sunlight into each of these barns, keeping cows from bunching during the summer.
Fly worry can also be an issue in some barns, especially when the manure lagoon is located close to one end of the barn. Cattle have innate behavioral responses to flies. Heel flies (Hypoderma bovis and lineatum) promote a ‘gadding’ reaction in cattle at pasture where the cows run around with their tails in the air. In freestall barns, flies of various types appear to promote bunching and avoidance behavior.
Emptying the manure lagoon, general fly control, removal of vegetation around the barn, and use of pour-on insecticides may help resolve the situation. The fly population on dairy farms has also been shown to be decreased by the use of in-feed chitin inhibitors that disrupt the development of fly larvae and reduce the emergence of adult flies from the manure of treated animals by preventing exoskeleton formation.
In the following video, notice how these tail-docked cows are bothered by flies. Although there is a very large amount of space at the feedbunk, they choose to stand together in an attempt to avoid flies, even as they aggressively interact with each other over feed space.