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Summer Bunching Signals Stress


Are your heifers bunching together in a pasture or barn? When you try to split them up, do they just avoid you and circle in tighter?

If so, they’re huddling up in response to stress, according to Iowa State University Extension Field Engineer, Brian Dougherty. “Bunching of animals is common in the summer months, even when animals have plenty of room to spread out,” he stated.

Dougherty said bunching is a natural response that animals use to cope with stress. Their natural herding instincts compel them to want to group together for relief. Unfortunately, the behavior often leads to even more stress. He identifies these common reasons why summertime bunching occurs:

1. Heat stress – Cattle are likely bunching due to heat if they exhibit the behavior when the ambient temperature or Temperature Humidity Index (THI) reaches a certain level, then spread out again when it drops.

2. Biting flies – Stable flies tend to rest on cattle’s legs and bellies and deliver a painful bite. Cattle often bunch with their heads to the center and tails to the outside to avoid stable flies. Horse and deer flies are blood feeders, and their bite also is painful. They are much larger than stable flies and often found near natural water sources. Horn flies are those small clouds of flies that swarm over animals’ backs. They are especially bothersome to pastured cattle. Face flies and houseflies do not bite, but do congregate on open wounds and around the nostrils and mouth.

3. Lack of fresh air – Poor ventilation inside barns may cause animals to bunch up near fresh air inlets or areas of faster-moving air. In naturally ventilated or hybrid ventilation barns, they may bunch more on days with slower wind speeds.

4. Light avoidance – Cattle are not bothered by bright light, but they do appear to associate light with heat due to their natural grazing instincts. When stressed, they may seek darker areas of the barn, even though those areas may be hotter.

Dougherty said there are solutions to each of these often-interrelated issues, which should be implemented to remove the underlying cause of stress. In addition, clean, cool, fresh water is always an important element to helping cattle manage summer stressors.



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