Understanding What Happened Back »

This article was written collaboratively by Dave Ollila and Rosie Nold.


The high death loss from the early October blizzard in South Dakota has producers and the public wondering “How could this happen?” We tend to think about winter storms, extreme cold and other stressful conditions that cattle, horses and sheep on western range often successfully cope with and ask “Why was this storm so much worse?”

A number of factors all happened simultaneously to create a situation of very high energy needs and high stress in cattle and other livestock. Any one of the following factors could have an impact by itself, but when all combined, it was simply too much for the animals and they most likely succumbed to hypothermia.

The contributing factors included:

  1. Animals were not adapted to winter conditions. Cattle will grow a thicker hair coat in response to shorter days, and cooler temperatures. But temperatures prior to the storm were in the 70°’s. For cattle, this meant they had thin hair coats and little protection from the elements.
  2. Snow was preceded by hours of rain. A wet hair coat reduces the “insulation” that the hair and hide provide and increases the rate of heat loss from the body. For example, a cow with a wet hair or summer hair coat has critical temperature of 59°, while one with a dry, heavy winter coat has a critical temperature of 18°. The critical temperature is the temperature at which the animal must increase its metabolism, or burn its own energy, to maintain its body temperature. The further the effective temperature is below the critical temperature, the more energy the animal must use to maintain its body temperature. See Spring Storms and Cold Stress for more detailed information.
  3. Winds in this blizzard were recorded up to 60 mph. Both research and practical experience show what a difference “wind chill” has on effective temperature. The range and pastures that are grazed during summer months are typically “open” – without constructed windbreaks, and usually very few natural windbreaks. With the storm so early in the year, most livestock were still out on summer range and pastures. Thus, animals felt the full intensity of the wind.
  4. The hair coat, temperature, moisture and wind combination meant the animals’ energy needs to maintain body temperature were much higher than even during a “normal” winter blizzard.
  5. Coupled with the very high energy needs of the animals was the fact that most of the feed the cattle were currently eating was quite low in energy. Cattle grazing lush green grass makes a beautiful picture, but the reality is that lush, rapidly growing green grass is very high in moisture and low in energy per pound of feed consumed. The unusually large rainfall in September had created this rapidly growing grass in many areas. Under normal weather conditions, cattle were able to consume large quantities of grass to meet and even exceed their energy needs. But under blizzard conditions, it was not possible for them to consume adequate amounts of forage to meet their much higher than normal energy needs.
  6. To try to escape or reduce the harsh wind, cattle will walk with the wind and seek areas of shelter, such as draws and ravines. Walking through heavy, wet and deep snow increased their energy needs even more. The severity of the snow fall also meant that the animals were walking blind, and could easily fall in to gullies, walk into a stock dam or creek, or gather into a fence corner and face crushing and trampling.

With all the factors above combining effects, exhaustion and the inability to maintain their own body temperature finally caused cattle to simply stop and succumb to hypothermia. It’s important to note that the factors above were beyond the control of ranchers, owners, or anyone else.

Cattle that survived the storm most likely have used up all or most of their energy reserves. This means they may need more supplemental feed than is normal for this time of year, particularly if there is added stress from rain and colder temperatures.

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